The vast majority of bacteria are unicellular. In cell shape, they can be rounded (cocci), rod-shaped (bacilli, clostridia, pseudomonads), convoluted (vibrios, spirillae, spirochetes), less often - stellate, tetrahedral, cubic, C- or O-shaped. The shape determines the ability of bacteria, such as attachment to the surface, mobility, absorption of nutrients. It has been noted, for example, that oligotrophs, that is, bacteria that live with a low content of nutrients in the medium, tend to increase the surface-to-volume ratio, for example, through the formation of outgrowths (so-called prostheses).
Three essential cellular structures are distinguished: * nucleoid * ribosomes * cytoplasmic membrane (CPM)
On the outside of the CPM, there are several layers (cell wall, capsule, mucous membrane), called the cell membrane, as well as surface structures (flagella, villi). The CPM and the cytoplasm are grouped together into the concept of protoplast.
2. Genetics of viruses. Viruses pathogenic for humans have two main properties - heredity and variability, the study of which is the subject of a special scientific discipline - genetics of viruses. Population structure of viruses and the nature of the processes occurring in them is determined by the following factors. High population size, which increases the likelihood of mutations that can be picked up by natural selection when the conditions for the existence of viruses change. Rapid change of generations allows you to study the variability of viruses not only in experiment, but also to observe their natural evolution in nature. Haploid and asexual reproduction determine: the genetic purity of the population (no hybrids); the impossibility of preserving the reserves of variability due to diploidy; immediate entry of mutants under selection control.
Small genome capacity and absence of repetitive genes... For the implementation of the infectious cycle, the functional integrity of all genes is required.
A slight change in one of them can cause a lethal or conditionally lethal effect on the virus.
Continuity in the dynamics of the epidemic process, since a prerequisite for conservation in nature is the transfer to new sensitive hosts. Viral populations well adapted to external conditions and do not undergo significant changes over a long period of time. When conditions change for the survival of the population, it becomes necessary restructuring of the hereditary structure, providing adaptation to the new environment. Such a restructuring is possible only if there is a population of altered genes in the general gene pool. Gene pool of viral populations is created and replenished from four main sources: internal factors: mutations, recombinations. External: inclusion of the host cell genetic material into the genome (the appearance of genomes containing new material), phenotypic mixing (enrichment of the gene pool due to the influx of genes from other viral populations).
3. The causative agents of cholera. Taxonomy. Characteristic. Microbiological diagnostics. Specific prophylaxis and treatment. Family Vibrionaceae, genus Vibrio, view V. cholerae. Cholera - ancient anthroponosis; since the time of Hippocrates it is known as "magi mara" - "great pestilence". Has claimed millions of lives. Quarantine infection.
Morphology. Gram (-), slightly curved rods (a kind of comma.spores and capsules (except for the Bengal strain) do not form; the Bengal strain forms a capsule in the body. Obligate aerobes. Monotrichs, the length of the flagellum can be 2-3 times the length of the soma, which causes a high mobility. Cultural properties. Grow well on simple nutrient media with an alkaline reaction (pH 8.5 - 9.5). On 1% peptone water forms a delicate film (aerobic). On alkaline agar- more often smooth transparent colonies with a bluish tinge, less often (in the process of dissociation) - rough and folded colonies. Biochemical properties. In laboratory practice, it is used biochemical classification according to Heiberg(for the whole genus Vibrio). There are 8 groups, cholera pathogens belong to 1st group(mannose k, sucrose k, arabinose -). Form indole. Antigenic structure:(1) general view specific H-AG - flagellate (2) like specific O-AG - somatic 80 serogroups are distinguished by O-AG; V. cholerae, el-tor - serogroup 01 (02 causes enteritis, gastroenteritis). O1-AG consists of fractions A, B and C, their combinations form serovars. 3 serovar : Inaba (AC), Ogawa (AB) (main pathogens), Gikoshima (ABC) (intermediate). Strain bengal - serovar 0-139. Pathogenicity factors:(1) flagella- active promotion of bacteria to enterocytes in the mucus layer; (2) adhesiveness- drank; (3) capsule in the Bengal strain; (4) toxins: 1 type - endotoxin(O-AG), 2 types - exoenterotoxin- cholerogen, the main symptom; identical in all three pathogens. 2 subunits: B - non-toxic, promotes toxin adhesion to enterocytes; A - the toxin itself, penetrates into the enterocytes, where it activates the AC, which leads to the accumulation of cAMP, which enhances the secretion of water, sodium and chlorine from the cells and disrupts the absorption of potassium; 3 types - thermostable toxin, affects sodium-potassium ATPase; as a result - diarrhea, severe dehydration; (5) neuraminidase- promotes adhesion of vibrios on enterocytes and penetration into the cell; Disease.A source- patient, vibrio carrier. Storage tank- hydrobionts. Infection path- alimentary, when drinking contaminated water (vegetables, aquatic organisms, etc.). Main clinical forms- cholera enteritis, gastroenteritis. Incubation period- several hours - 6 days. First symptom- diarrhea, Second symptom- profuse repeated vomiting by a fountain, dehydration, desalination of the body, muscle weakness, dizziness, hoarseness of the voice, a sharp loss of skin turgor. Microbiological diagnostics: (1) express methods: to determine the hypertension of pathogens: RIF, RNGA according to Rytsay, the method of immobilization of vibrios using O-cholera serum; accounting in a dark-field and phase-contrast microscope. (2) main method - bacteriological.(3) additional- serological: determination of vibriocidal antibodies in the patient's serum using the bacteriolysis reaction (for convalescents). (4) genetic- the use of molecular genetic probes for tox + genes of toxin pathogens. Treatment... First of all - the restoration of water-salt metabolism, and then - the use of antibiotics, chemotherapy. The restoration of water-salt metabolism should be carried out by introducing saline solutions per os or intravenously: KCl, NaCl, NaHCO3, glucose etc. The volume of fluid injected and removed must be strictly controlled. Prevention. 6 month immunity, does not prevent Bengal strain. 1) inactivated cholera corpuscular vaccine from V. cholerae, V. el-tor; 2) chemical cholera vaccine - mono (contains cholerogen-toxoid and O-AG of serovar Inaba); 3) chemical cholera vaccine - bi (serovars Ogawa, Inaba).
1.Principles of classification of bacteria. For bacteria the following taxonomic categories are recommended: class, division, order, family, genus, species. The species name corresponds to the binary nomenclature, that is, it consists of two words. For example, the causative agent of syphilis is written as Treponema pallidum. The first word is the name of the genus and is written with an uppercase letter, the second word denotes a species and is written with a lowercase letter. When the species is mentioned again, the generic name is abbreviated to the initial letter, for example: T.pallidum. Bacteria belong to prokaryotes, i.e. prenuclear organisms, since they have a primitive nucleus without a shell, nucleolus, histones, and there are no highly organized organelles in the cytoplasm Bacteria are divided into 2 domains:« Bacteria" and "Archaea". In the domain "Bacteria"The following bacteria can be distinguished:
1) bacteria with a thin cell wall, gram (-);
2) bacteria with a thick cell wall, gram (+);
3) bact. without CS (class Mollicutes - mycoplasma)
Archaebacteria do not contain peptidoglycan in the cell wall. They have special ribosomes and ribosomal RNA (rRNA). Among thin-walled grams of (-) eubacteria distinguish between:
Spherical forms, or cocci (gonococci, meningococci, veilonella);
Twisted forms - spirochetes and spirilla;
Rod-shaped forms, including rickettsia.
To thick-walled gram (+) eubacteria include:
Spherical forms, or cocci (staphylococci, streptococci, pneumococci);
Rod-shaped forms, as well as actinomycetes (branching, filamentous bacteria), corynebacteria (clavate bacteria), mycobacteria and bifidobacteria.
Thin-walled gram (-) bacteria: Meningococci, Gonococci, Veilonella, Sticks, Vibrios, Campylobacter, Helicobacterium, Spirilla, Spirochete, Rickettsia, Chlamydia.
Thick-walled gram (+) bacteria: Pneumococci, Streptococci, Staphylococci, Sticks, Bacilli, Clostridia, Corinebacteria, Mycobacteria, Bifidobacteria, Actinomycetes.
2. Mechanisms of drug resistance of pathogens of infectious diseases. Ways to overcome it. Antibiotic resistance is the resistance of microbes to antimicrobial chemotherapy drugs. Bacteria should be considered resistant if they are not neutralized by such drug concentrations that are actually created in the macroorganism. Resistance can be natural or acquired.
Natural resilience... Some types of microbes are naturally resistant to certain families of antibiotics, either as a result of the lack of an appropriate target (for example, mycoplasmas do not have a cell wall, therefore they are not sensitive to all drugs acting at this level), or as a result of bacterial impermeability to a given drug (for example, gram-negative microbes less permeable to large-molecular compounds than gram-positive bacteria, since their outer membrane has "small" pores).
Acquired resilience. The acquisition of resistance is a biological pattern associated with the adaptation of microorganisms to environmental conditions. It is, albeit to varying degrees, valid for all bacteria and all antibiotics. Not only bacteria adapt to chemotherapy drugs, but also other microbes - from eukaryotic forms (protozoa, fungi) to viruses. The problem of the formation and spread of drug resistance of microbes is especially significant for nosocomial infections caused by the so-called "hospital strains", which, as a rule, have multiple antibiotic resistance (so-called multidrug resistance).
The genetic basis of acquired resistance. Antibiotic resistance is determined and maintained by resistance genes (r-genes) and conditions conducive to their spread in microbial populations. Acquired drug resistance can arise and spread in a bacterial population as a result of:
Mutations in the chromosome of a bacterial cell with subsequent selection (i.e., selection) of mutants. Selection is especially easy in the presence of antibiotics, since under these conditions the mutants gain an advantage over the rest of the cells in the population that are sensitive to the drug. Mutations arise regardless of the use of the antibiotic, i.e., the drug itself does not affect the frequency of mutations and is not their cause, but serves as a selection factor. Further, resistant cells give rise to offspring and can be transferred into the body of the next host (human or animal), forming and spreading resistant strains. Mutations can be: 1) single (if the mutation occurred in one cell, as a result of which altered proteins are synthesized in it) and 2) multiple (a series of mutations, as a result of which not one, but a whole set of proteins changes, for example, penicillin-binding proteins in penicillin-resistant pneumococcus);
Transfer of transmissible resistance plasmids (R-plasmids). Resistance plasmids (transmissible) usually encode cross-resistance to several families of antibiotics. For the first time, such multiple resistance was described by Japanese researchers against intestinal bacteria. It has now been shown to be found in other groups of bacteria as well. Some plasmids can be transferred between bacteria of different species, so the same resistance gene can be found in bacteria that are taxonomically distant from each other. For example, beta-lactamase, encoded by the plasmid TEM-1, is widespread in gram-negative bacteria and is found in E. coli and other intestinal bacteria, as well as in gonococcus resistant to penicillin and Haemophilus influenzae resistant to ampicillin;
Transfer of transposons carrying r-genes (or migratory genetic sequences). Transposons can migrate from chromosome to plasmid and vice versa, as well as from plasmid to another plasmid. Thus, resistance genes can be transferred further to daughter cells or by recombination to other recipient bacteria.
Realization of acquired resilience. Changes in the bacterial genome lead to the fact that some properties of the bacterial cell also change, as a result of which it becomes resistant to antibacterial drugs. Usually, the antimicrobial effect of the drug is carried out in this way: the agent must contact the bacterium and pass through its membrane, then it must be delivered to the site of action, after which the drug interacts with intracellular targets. The realization of acquired drug resistance is possible at each of the following stages:
target modification... The target enzyme can be changed in such a way that its functions are not impaired, but the ability to bind to a chemotherapy drug (affinity) is sharply reduced, or a "bypass path" of metabolism can be switched on, that is, another enzyme is activated in the cell, which is not subject to the action of this drug ...
Target "inaccessibility" due to a decrease in the permeability of the cell wall and cell membranes or the "effluco mechanism, when the cell" pushes "the antibiotic out of itself.
inactivation preparation with bacterial enzymes. Some bacteria are capable of producing specific enzymes that make drugs inactive (for example, beta-lactamases, aminoglycoside-modifying enzymes, chloramphenicol acetyltransferase). Beta-lactamases are enzymes that break down the beta-lactam ring to form inactive compounds. The genes encoding these enzymes are widespread among bacteria and can be both in the chromosome and in the plasmid.
To combat the inactivating effect of beta-lactamases, inhibitor substances are used (for example, clavulanic acid, sulbactam, tazobactam). These substances contain a beta-lactam ring in their composition and are able to bind to beta-lactamases, preventing their destructive effect on beta-lactams. At the same time, the intrinsic antibacterial activity of such inhibitors is low. Clavulanic acid inhibits most of the known beta-lactamases. It is combined with penicillins: amoxicillin, ticarcillin, piperacillin.
It is almost impossible to prevent the development of antibiotic resistance in bacteria, but it is necessary to use antimicrobial drugs in such a way as not to promote the development and spread of resistance (in particular, to use antibiotics strictly according to indications, to avoid their use for prophylactic purposes, after 10-15 days of antibiotic therapy change the drug, use drugs with a narrow spectrum of action if possible, use antibiotics in veterinary medicine with limited use and not use them as a growth factor).
Lecture No. 5 Morphology and taxonomy of microorganisms. Prokaryotes (bacteria and actinomycetes).
1 Morphology and taxonomy of microorganisms. The morphology of microorganisms studies their appearance, shape and structural features, the ability to move, spore formation, methods of reproduction. Morphological features play an important role in the recognition and classification of microorganisms. Since ancient times, the living world has been divided into two kingdoms: the kingdom of plants and the kingdom of animals. When the world of microorganisms was discovered, they were isolated into a separate kingdom. Thus, until the 19th century, the whole world of living organisms was divided into three kingdoms. At the beginning, the classification of microorganisms was based on morphological signs, since a person knew nothing more about them. By the end of the 19th century, many species were described; different scientists, mainly botanists, divided microorganisms into groups adopted for the classification of plants. In 1897, for the taxonomy of microbes, they began to use, along with morphological, and physiological signs. As it turned out later, for a scientifically grounded classification, some signs alone are not enough. Therefore, a set of features is used:
Morphological (cell shape, size, mobility, reproduction, sporulation, Gram stain);
Cultural (the nature of growth on liquid and solid nutrient media);
Physiological and biochemical (the nature of the accumulated products);
Genotypic (physical and chemical properties of DNA).
Genosystematics makes it possible to determine the type of microorganisms not by similarity, but by kinship. It was found that the nucleotide composition of the total DNA does not change during the development of microorganisms under different conditions. S- and R-forms are identical in DNA composition. Found and such microorganisms that have a similar nucleotide composition of DNA, although they belong to different systematic groups: Escherichia coli and some corynebacteria. This indicates that in the systematics (taxonomy) of microbes, different characters should be taken into account.
Until recently, all living things of a cellular structure, depending on the relationship of the nucleus and organelles with the cytoplasm, the composition of the cell wall and other characteristics, were divided into two groups (kingdoms):
1.1 Prokaryotes-prenuclear (referred to - organisms that do not have a well-defined nucleus, represented by a DNA molecule in the form of a ring; peptidoglycan (murein) and teichoic acids are part of the cell wall; ribosomes have sedimentation constants 70; energy centers of the cell are located in mesosomes and there are no organelles ).
1.2 Eukaryotes are nuclear (with a well-defined nucleus separated from the cytoplasm by a membrane; peptidoglycan and teichoic acids are absent in the cell wall; cytoplasmic ribosomes are larger; sedimentation constant 80; energy processes are carried out in mitochondria; organelles have a Golgi complex, etc.).
Later it turned out that among microorganisms there are also non-cellular forms-viruses and therefore a third group (kingdom) was identified - vira.
To designate microorganisms, a double (binary) nomenclature is adopted, which includes the name of the genus and species. A generic name is written with a capital letter (capital), a specific name (even derived from a surname) - with a lowercase (small). For example, the anthrax bacillus is called Bacillus anthracis, Escherichia coli, and Aspergillus niger.
The main (lowest) taxonomic unit is the species. Species are grouped into genera, genera - into families, families - into orders, orders - into classes, classes - into divisions, divisions - into kingdoms.
A species is a collection of individuals of the same genotype with a pronounced phenotypic similarity.
Culture - microorganisms obtained from an animal, human, plant or substrate of the external environment and grown on a nutrient medium. Pure cultures consist of individuals of the same species (offspring obtained from one cell - a clone).
A strain is a culture of the same species isolated from different habitats and differing in insignificant changes in properties. For example, E. coli isolated from the human body, cattle, water bodies, soil, can be of different strains.
2 Prokaryotes (bacteria and actinomycetes). Bacteria (prokaryotes) are a large group of microorganisms (about 1600 species), most of which are unicellular. The shape and size of bacteria. The main forms of bacteria are spherical, rod-shaped and convoluted. Spherical bacteria - cocci have the usual shape of a ball, they are flattened, oval or bean-shaped. Cocci can be in the form of single cells - monococci (micrococci) or combined in various combinations: in pairs - diplococci, four cells each - tetracocci, in the form of more or less long chains - streptococci, as well as in the form of cubic clusters (in the form of packages) of eight cells, located in two tiers one above the other, - sarcins. There are clusters of irregular shapes, resembling bunches of grapes - staphylococci. Rod-shaped bacteria can be single or connected in pairs - diplobacteria, chains of three to four or more cells - streptobacteria. The relationship between the length and thickness of sticks is very different. Twisted, or curved, bacteria vary in length, thickness, and degree of curvature. Sticks slightly curved in the form of a comma are called vibrios, sticks with one or more curls in the form of a corkscrew are called spirillae, and thin sticks with numerous curls are called spirochetes. Thanks to the use of an electron microscope to study microorganisms in natural natural substrates, bacteria have been found that have a special cell shape: a closed or open ring (toroids); with outgrowths (stitches); worm-shaped - long with curved very thin ends; and also in the form of a hexagonal star.
The size of bacteria is very small: from tenths of a micrometer (μm) to a few micrometers. On average, the body size of most bacteria is 0.5-1 microns, and the average length of rod-shaped bacteria is 2-5 microns. There are bacteria that are much larger than the average size, and some are on the verge of visibility in conventional optical microscopes. The body shape of bacteria, as well as their size, can vary depending on age and growth conditions. However, under certain relatively stable conditions, the bacteria retain their inherent size and shape. The mass of a bacterial cell is very small, approximately 4-10-1 :! G.
Bacterial cell structure . The cell of prokaryotic organisms, which include bacteria, has fundamental ultrastructure features. The cell wall (membrane) is an important structural element of most bacteria. The cell wall accounts for 5 to 20% of the dry matter of the cell. It has elasticity, serves as a mechanical barrier between the protoplast and the environment, and gives the cell a certain shape. The cell wall contains a heteropolymeric compound specific for prokaryotic cells - peptidoglycan (murein), which is absent in the cell walls of eukaryotic organisms. According to the staining method proposed by the Danish physicist H. Gram (1884), bacteria are divided into two groups: gram-positive and gram-negative. Gram-positive cells retain the dye, while gram-negative cells do not, which is due to differences in the chemical composition and ultrastructure of their cell walls. In gram-positive bacteria, the cell walls are thicker, amorphous, they contain a large amount of murein (from 50 to 90% of the dry mass of the cell wall) and teichoic acids. The cell walls of gram-negative bacteria are thinner, layered, they contain a lot of lipids, little murein (5-10%), and there are no teichoic acids.
The cell wall of bacteria is often covered in mucus. The mucous layer can be thin, barely distinguishable, but it can be significant, it can form a capsule. Often, the capsule is much larger than the bacterial cell in size. The sludge of the cell walls is sometimes so strong that the capsules of individual cells merge into mucous masses (zoogels), in which bacterial cells are interspersed. The mucous substances formed by some bacteria are not retained as a compact mass around the cell wall, but diffuse into the environment. When they multiply rapidly in liquid substrates, mucus-forming bacteria can turn them into a continuous mucous mass. This phenomenon is sometimes observed in sugary extracts from beets in the production of sugar. In a short time, the sugar syrup can turn into a viscous mucous mass. Meat, sausages, cottage cheese are subject to slime; the viscosity of milk, pickles, pickled vegetables, beer, wine is observed. The intensity of mucus formation and the chemical composition of mucus depend on the type of bacteria and cultivation conditions. The capsule has useful properties, mucus protects cells from unfavorable conditions - in many bacteria, mucus production increases under such conditions. The capsule protects the cell from mechanical damage and drying out, creates an additional osmotic barrier, serves as an obstacle to the penetration of phages, antibodies, and sometimes it is a source of reserve nutrients. The cytoplasmic membrane separates the contents of the cell from the cell wall. This is an obligatory structure of any cell. If the integrity of the cytoplasmic membrane is violated, the cell loses its viability. The cytoplasmic membrane accounts for 8-15% of the dry matter of the cell. The membrane contains up to 70-90% of cell lipids, its thickness is 7-10 nm 1. On cell sections in an electron microscope, it is visible in the form of a three-layer structure - one lipid layer and two protein layers adjacent to it on both sides. The cytoplasmic membrane in places invades into the cell, forming all kinds of membrane structures. It contains various enzymes; it is semi-permeable, plays an important role in the exchange of substances between the cell and the environment. The cytoplasm of a bacterial cell is a semi-liquid, viscous, colloidal system. In some places, it is permeated with membrane structures - mesosomes, which originated from the cytoplasmic membrane and retained a connection with it. Mesosomes have different functions; in them and in the cytoplasmic membrane associated with them, there are enzymes involved in energy processes - in the supply of energy to the cell. Well-developed mesosomes are found only in gram-positive bacteria, in gram-negative they are poorly developed and have a simpler structure. The cytoplasm contains ribosomes, a nuclear apparatus and various inclusions. Ribosomes are scattered in the cytoplasm in the form of granules with a size of 20-30 nm; ribosomes are composed of approximately 60% ribonucleic acid (RNA) and 40% protein. Ribosomes are responsible for cell protein synthesis. In a bacterial cell, depending on its age and living conditions, there may or may be 5-50 thousand ribosomes. The nuclear apparatus of bacteria is called the nucleoid. Electron microscopy of ultrathin sections of a bacterial cell made it possible to establish that the carrier of the cell's genetic information is a molecule of deoxyribonucleic acid (DNA). DNA is in the form of a double helical strand closed in a ring; it is also called the "bacterial chromosome". It is located in a certain area of the cytoplasm, but is not separated from it by its own membrane.
Cytoplasmic inclusions bacterial cells are diverse, mainly storage nutrients that are deposited in cells when they develop in conditions of excess nutrients in the environment, and are consumed when cells are under starvation conditions. Bacterial cells deposit polysaccharides: glycogen, the starch-like substance of granulosis, which is used as a source of carbon and energy. Lipids are found in cells in the form of granules and droplets. Fat is a good source of carbon and energy. Many bacteria accumulate polyphosphates; they are contained in volutin granules and are used by cells as a source of phosphorus and energy. Molecular sulfur is deposited in the cells of sulfur bacteria.
Motility of bacteria . Globular bacteria are usually immobile. Rod-shaped bacteria are both mobile and immobile. Curved and coiled bacteria are mobile. Some bacteria move by sliding. Most bacteria move by flagella. Flagella are thin, spirally twisted protein filaments that can rotate. The length of the flagella is different, and the thickness is so small (10-20 nm) that they can be seen in a light microscope only after special processing of the cell. The presence, number and location of flagella are constant signs for the species and have diagnostic value. Bacteria with one flagellum at the end of the cell are called monotrichs; with a bundle of flagella - lophotrichs ", with a bundle of flagella at both ends of the cell - amphitrichs; bacteria in which flagella are located on the entire surface of the cell are called peritrichous. The speed of movement of bacteria is high: in a second, a cell with flagella can travel 20-50 times more than the length of its body.Under unfavorable living conditions, with aging of the cell, with mechanical action, mobility can be lost.In addition to flagella, on the surface of some bacteria there are a large number of filamentous formations, much thinner and shorter than flagella - fimbriae (or drank) ...
Reproduction of bacteria. For prokaryotic cells, simple cell division in two is characteristic. Cell division begins, as a rule, some time after nucleoid division. Rod-shaped bacteria divide across, spherical in shape in different planes. Depending on the orientation of the division plane and their number, various forms arise: single cocci, paired, chains, in the form of packages, bunches. A feature of the reproduction of bacteria is the speed of the process. The rate of division depends on the type of bacteria, the cultivation conditions: some species divide every 15-20 minutes, others - after 5-10 hours. With this division, the number of bacterial cells per day reaches a huge number. This is often observed in food products: rapid souring of milk due to the development of lactic acid bacteria, rapid spoilage of meat and fish due to the development of putrefactive bacteria, etc.
Spore formation. Spores in bacteria are usually formed under unfavorable conditions of development: with a lack of nutrients, changes in temperature, pH, with the accumulation of metabolic products above a certain level. The ability to form spores is possessed mainly by rod-shaped bacteria. Only one spore (endospore) is formed in each cell.
Spore formation is a complex process, several stages are distinguished in it: first, a restructuring of the genetic apparatus of the cell is observed, the morphology of the nucleoid changes. DNA synthesis stops in the cell. Nuclear DNA is pulled out as a strand, which then splits; part of it is concentrated at one of the poles of the cell. This part of the cell is called the sporogenic zone. In the sporogenic zone, the cytoplasm thickens, then this area is separated from the rest of the cellular contents by a septum (septum). The cut off area is covered with a membrane of the mother cell, the so-called prospore is formed. A prospore is a structure located inside the mother cell, from which it is separated by two membranes: an outer and an inner one. A cortical layer (cortex) is formed between the membranes, which is similar in chemical composition to the cell wall of a vegetative cell. In addition to peptidoglycan, the cortex contains dipicolinic acid (C 7 H 8 O 4 Mg), which is absent in vegetative cells. Subsequently, a spore shell is formed on top of the prospore, consisting of several layers. The number, thickness and structure of the layers are different for different types of bacteria. The surface of the outer shell can be smooth or with outgrowths of various lengths and shapes. On top of the spore shell, a still thin cover is often formed that surrounds the spore in the form of a cover - exosporium.
Spores are usually round or oval in shape. The diameter of the spores of some bacteria exceeds the width of the cell, as a result of which the shape of the spore-bearing cells changes. The cell takes on the shape of a spindle (clostridium) if the spore is located in its center, or the shape of a drumstick (plectridium) when the spore is near the end of the cell.
After the maturation of the spore, the mother cell dies, its membrane is destroyed, and the spore is released. The spore formation process takes several hours.
The presence of a dense, difficult-to-penetrate membrane in bacterial spores, a low content of water in it, a large amount of lipids, as well as the presence of calcium and dipicolinic acid cause high spore resistance to environmental factors. Spores can be viable for hundreds or even thousands of years. For example, viable spores have been isolated from the corpses of mammoths and Egyptian mummies dating back thousands of years. Spores are resistant to high temperatures: in a dry state, they die after heating at 165-170 ° C for 1.5-2 hours, and with superheated steam (in an autoclave) at 121 ° C for 15-30 minutes.
In favorable conditions, the spore grows into a vegetative cell; this process usually takes several hours.
The germinating spore begins to actively absorb water, its enzymes are activated, and biochemical processes that lead to growth are intensified. During spore germination, the cortex turns into the cell wall of a young vegetative cell; dipicolinic acid and calcium are released into the external environment. The outer shell of the spore ruptures, through the breaks a "sprout" of a new cell emerges from which a vegetative bacterial cell is then formed.
Food spoilage is caused only by vegetative cells. Knowledge of the factors contributing to the formation of spores in bacteria, and the factors that cause their germination into vegetative cells, is important in choosing the method of processing products in order to prevent their microbial spoilage.
The above information characterizes mainly the so-called true bacteria. There are others, more or less different from them, which include the following.
Filamentous (filamentous bacteria). These are multicellular organisms in the form of filaments of various lengths, with a diameter of 1 to 7 microns, mobile or attached to a substrate. Mostly threads with a slimy sheath. They may contain magnesium oxide or iron oxides. They live in water bodies, they are found in the soil.
Myxobacteria. These are rod-shaped bacteria that move by sliding. They form fruiting bodies - clusters of cells enclosed in mucus. The cells in the fruiting bodies pass into a dormant state - mixospores. These bacteria live in the soil, on various plant debris.
Budding and stalk bacteria reproduce by budding, stalking, or both. There are species with outgrowths - stitches. They live in soil and water bodies.
Actinomycetes. The bacteria are branched. Some are slightly branched rods (see Fig. 2, e), others are in the form of thin branching filaments that form a unicellular mycelium. Mycelial actinomycetes, called "radiant fungi", multiply by spores that develop on the aerial branches of the mycelium. Actinomycetes are colored; they are widespread in nature. They are also found on food and can cause spoilage. The product takes on a characteristic earthy odor. Many actinomycetes produce antibiotics. There are species that are pathogenic for humans and animals.
Mycoplasma. Organisms without a cell wall are covered only by a three-layer membrane. The cells are very small, sometimes ultramicroscopic in size (about 200 nm), pleomorphic (of various shapes) - from coccoid to filamentous. Some cause diseases in humans, animals, plants.
Basics of bacterial taxonomy Modern systems for the classification of bacteria are essentially artificial, grouping bacteria into certain groups based on their similarity in a complex of morphological, physiological, biochemical and genotypic characteristics. For this purpose, Bergi's guidelines for the definition of bacteria are used (1974, 8th edition and 1984. - 9th edition). According to the 8th edition, all prokaryotes are divided into two sections - cyanobacteria and bacteria. The first section - cyanobacteria (blue-green algae) - are phototrophic microorganisms. The second section is bacteria. This department is divided into 19 groups. The 17th group includes actinomycetes. According to the 9th edition, the kingdom of prokaryotes is subdivided into four sections, depending on the presence or absence of a cell wall and its chemical composition: the first section - thin-skinned, includes groups of bacteria, gram-negative, phototrophic and cyanobacteria; in the 2nd section - hard-skinned, includes groups of bacteria related to positive Gram stain; the third section includes mycoplasma - bacteria that do not have a cell wall; the fourth section includes methane-forming and archaebacteria (a special group of bacteria that live in extreme environmental conditions and are one of the most ancient forms of life).
Classification of bacteria... The decision of the International Code for bacteria recommended the following taxonomic categories: class, division, order, family, genus, species. The species name corresponds to the binary nomenclature, that is, it consists of two words. For example, the causative agent of syphilis is written as Treponema pallidum. The first word is on
the title of the genus is written with a capital letter, the second word denotes a species and is written with a lowercase letter. When the species is mentioned again, the generic name is abbreviated to the initial letter, for example: T.pallidum.
Bacteria are classified as prokaryotes, i.e. pre-nuclear organisms, since they have a primitive nucleus without a shell, nucleolus, histones. and there are no highly organized organelles in the cytoplasm (mitochondria, Golgi apparatus, lysosomes, etc.)
In Burgey's old Guide to Systematic Bacteriology, bacteria were divided according to the characteristics of the bacterial cell wall into 4 sections: Gracilicutes - eubacteria with a thin cell wall, gram-negative; Firmicutes - eubacteria with a thick cell wall, gram-positive; Tenericutes - eubacteria without a cell wall; Mendosicutes - archaea with a defective cell wall.
Each department was divided into sections, or groups, according to Gram stain, cell shape, oxygen demand, mobility, metabolic and nutritional characteristics.
According to the 2nd edition (2001) of the GuidelinesBurgey, bacteria are divided into 2 domains:"Bacteria" and "Archaea" (Table 2.1).
Table. Domain characteristicsBacteriaandArchaea
|
Domain"Bacteria"(eubacteria) |
DomainArchaea "(archaebacteria) |
|
In the domain "Bacteria" one can distinguish the following bacteria: 1) bacteria with a thin cell wall, gram-negative *; 2) bacteria with a thick cell wall, gram-positive **; 3) bacteria beta cell wall (class Mollicutes - mycoplasma) |
Archbacteria do not contain peptidoglycan in the cell wall. They have special ribosomes and ribosomal RNAs (rRNAs). The term "archaebacteria - appeared in 1977. It is one of the ancient forms of life, as indicated by the prefix" arche ". There are no infectious agents among them. |
* Among thin-walled gram-negative eubacteria distinguish between:
spherical forms, or cocci (gonococci, meningococci, veilonella);
convoluted forms - spirochetes and spirillae;
rod-shaped forms, including rickettsia.
** To thick-walled gram-positive eubacteria include:
spherical forms, or cocci (staphylococci, streptococci, pneumococci);
rod-shaped forms, as well as actinomycetes (branching, filamentous bacteria), corynebacteria (clavate bacteria), mycobacteria and bifidobacteria (Fig. 2.1).
Most gram-negative bacteria are grouped into a type of proteobacteria. based on the similarity in ribosomal RNA "Proteobacteria" - named after the Greek god Proteus. taking on various forms). They appeared from general photosynthesis. tic ancestor.
Gram-positive bacteria, according to the studied sequences of ribosomal RNA, are a separate phylogenetic group with two large subdivisions - with a high and a low ratio G+ C (genetic similarity). Like proteobacteria, this group is metabolically diverse.
To the domain "Bacteria»Includes 22 types, of whichThe following are of medical importance:
Type ofProteobacteria
Class Alphaproteobacteria. Childbirth: Rickettsia, Orientia, Ehrlichia, Bartonella, Brucella
Class Betaproteobacteria. Childbirth: Burkholderia, Alcaligenes, Bordetella, Neisseria, Kingella, Spirillum
Class Gammaproteobacteria. Childbirth: Francisella, Legionella, Coxiella, Pseudomonas, Moraxella, Acinetobacter, Vibrio, Enterobacter, Callimatobacterium, Citrobacter, Edwardsiella, Erwinia, Escherichia, Hafnia, Klebsiella, Morganella, Proteus, Providencia, Salmonella, Serrateersia, Shigella
Class Deltaproteobacteria. Genus: Bilophila
Class Epsilonproteobacteria. Childbirth: Campylobacter, Helicobacter, Wolinella
Type ofFirmicutes (the mainwaygrampolo zhivnye)
Class Clostridia. Childbirth: Clostridium, Sarcina, Peptostreptococcus, Eubacterium, Peptococcus, Veillonella (gram negative)
Class Mollicutes. Childbirth: Mycoplasma, Ureaplasma
Class Bacilli. Childbirth: Bacillus, Sporosarcina, Listeria, Staphylococcus, Gemella, Lactobacillus, Pediococcus, Aerococcus, Leuconostoc, Streptococcus, Lactococcus
Type ofActinobacteria
Class Actinobacteria. Childbirth: Actinomyces, Arcanodacterium, Mobiluncus, Micrococcus, Rothia, Stomatococcus, Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, Bifidobacterium, Gardnerella
Type ofClamydiae
Class Clamydiae. Childbirth: Clamydia, Clamydophila
Type ofSpirochaetes
Class Spirochaetes. Childbirth: Spirochaeta, Borrelia, Treponema, Leptospira
Bacteroidetes type
Class Bacteroidetes. Childbirth: Bacteroides, Porphyromonas, Prevotella
Class Flavobacteria. Childbirth: Flavobacterium
The division of bacteria according to the structural features of the cell wall is associated with the possible variability of their color in a particular color according to the Gram method. According to this method, proposed in 1884 by the Danish scientist H. Gram, depending on the results of staining, bacteria are divided into gram-positive, stained in blue-violet, and gram-negative, stained in red. However, it turned out that bacteria with the so-called gram-positive type of cell wall (thicker than that of gram-negative bacteria), for example, bacteria of the genus Mobiluncus and some spore-forming bacteria, instead of the usual gram-positive color, have a gram-negative color. Therefore, for the taxonomy of bacteria, the features of the structure and chemical composition of cell walls are of greater importance than Gram staining.
2.2.1. Forms of bacteria
There are several main forms of bacteria (see Fig. 2.1) - coccoid, rod-shaped, convoluted and branching, filamentous forms of bacteria.
Spherical forms, or cocci,- globular bacteria with a size of 0.5-1.0 microns *, which, according to their relative position, are divided into micrococci, diplococci, streptococci, tetracocci, sarcins and staphylococci.
Micrococci(from the Greek. micros - small) - separately located cells.
Diplococci(from the Greek. diploos - double), or paired cocci, are arranged in pairs (pneumococcus, gonococcus, meningococcus), since the cells do not diverge after division. Pneumococcus (the causative agent of pneumonia) has a lanceolate shape on opposite sides, and gonococcus(the causative agent of gonorrhea) and meningococcus (the causative agent of epidemic meningitis) are in the form of coffee beans facing with a concave surface towards each other.
Streptococci(from the Greek. streptos - chain) - cells of a rounded or elongated shape, making up a chain due to cell division in one plane and preservation of the connection between them at the place of division.
Sarcinas(from lat. sarcina - bundle, bale) are arranged in the form of packages of 8 or more cocci, since they are formed during cell division in three mutually perpendicular planes.
Staphylococci(from the Greek. staphyle - bunch of grapes) - cocci, arranged in the form of a bunch of grapes as a result of division in different planes.
Rod-shaped bacteria differ in size, shape of the ends of the cells and the mutual arrangement of cells. The length of the cells varies from 1.0 to 10 µm, the thickness is from 0.5 to 2.0 µm. Coli can be correct (E. coli, etc.) and incorrect (corynebacterium and etc.) forms, including branching, for example, in actinomycetes. The smallest rod-shaped bacteria are rickettsia.
The ends of the sticks can be cut off (anthrax bacillus), rounded (Escherichia coli), pointed (fusobacteria) or in the form of a thickening. In the latter case, the stick looks like a mace (corynebacterium diphtheria).
The slightly curved rods are called vibrios (Vibrio cholerae). Most rod-shaped bacteria are randomly located, as cells diverge after division. If after division the cells remain connected -
with common fragments of the cell wall and do not diverge, then they are located at an angle to each other (corynebacterium diphtheria) or form a chain (anthrax bacillus).
Curvy shapes- spiral bacteria, for example spirilla, having the appearance of corkscrew-like convoluted cells. Pathogenic spirillum includes the causative agent sodoku (rat bite disease). Crimped also include cam-pylobacteria and helicobacteria, which have bends like the wing of a flying gull; bacteria such as spirochetes are also close to them. Spirochetes- thin, long, crimped
spiral-shaped) bacteria that differ from spirilla in mobility due to flexion changes in cells. Spirochetes are composed of an outer membrane
cell wall), surrounding a protoplasmic cylinder with a cytoplasmic membrane and an axial filament (axistil). The axial filament is located under the outer membrane of the cell wall (in the periplasm) and, as it were, twists around the protoplasmic cylinder of the spirochete, giving it a helical shape (primary curls of the spirochetes). The axial filament consists of periplasmatic fibrils, analogs of bacterial flagella, and is a contractile protein called flagellin. Fibrils are attached to the ends of the cell (Fig. 2.2) and are directed towards each other. The other end of the fibrils is free. The number and location of fibrils vary from species to species. Fibrils are involved in the movement of spirochetes, imparting rotational, flexion and translational movement to the cells. In this case, the spirochetes form loops, curls, bends, which are called secondary curls. Spirochetes
dyes are poorly perceived. Usually they are stained according to Romanovsky-Giemsa or silvering. In live form, spirochetes are examined using phase contrast or dark-field microscopy.
Spirochetes are represented by 3 genera pathogenic for humans: Treponema, Borrelia, Leptospira.
Treponema(genus Treponema) have the appearance of thin corkscrew-like twisted threads with 8-12 uniform small curls. 3-4 fibrils (flagella) are located around the protoplast of treponemes. The cytoplasm contains cytoplasmic filaments. Pathogenic representatives are T.pallidum - the causative agent of syphilis, T.pertenue - the causative agent of tropical disease is fram-bezia. There are also saprophytes - inhabitants of the human mouth, silt of reservoirs.
Borrelia(genus Borrelia), unlike treponemas, they are longer, have 3-8 large curls and 7-20 fibrils. These include the causative agent of relapsing fever (V.recurrentis) and the causative agents of Lyme disease (V.burgdorferi and etc.).
Leptospira(genus Leptospira) have shallow and frequent curls - in the form of a twisted rope. The ends of these spirochetes are curved like hooks with thickened ends. Forming secondary curls, they take the form of letters S or with; have 2 axial filaments (flagella). Pathogenic representative L. in terrogans causes leptospirosis when ingested with water or food, leading to the development of hemorrhages and jaundice.
in the cytoplasm, and some in the nucleus of infected cells. They live in arthropods (lice, fleas, ticks), which are their hosts or carriers. Rickettsiae got their name from H. T. Ricketts, an American scientist who first described one of the pathogens (Rocky Mountain spotted fever). The shape and size of rickettsia can vary (irregularly shaped, filamentous cells) depending on the growth conditions. The structure of rickettsia does not differ from that of gram-negative bacteria.
Rickettsiae have a metabolism independent of the host cell; however, it is possible that they receive macroergic compounds from the host cell for their reproduction. In smears and tissues, they are stained according to Romanovsky-Giemsa, according to Macchiavello-Zdrodovsky (rickettsia is red, and infected cells are blue).
In humans, rickettsiae cause epidemic typhus (Rickettsia prowazekii), tick-borne rickettsiosis (R. sibirica), Rocky Mountain spotted fever (R. rickettsii) and other rickettsioses.
Elementary bodies enter the epithelial cell by endocytosis with the formation of an intracellular vacuole. Inside the cells, they enlarge and turn into dividing reticular bodies, forming clusters in vacuoles (inclusions). Elementary bodies are formed from the reticular bodies, which leave the cells by exocytosis or cell lysis. Coming out of
elementary body cells enter a new cycle, infecting other cells (Fig. 16.11.1). In humans, chlamydiae cause damage to the eyes (trachoma, conjunctivitis), uro-genital tract, lungs, etc.
Actinomycetes- branching, filamentous or rod-shaped gram-positive bacteria. Its name (from the Greek. actis - Ray, mykes - mushroom) they received in connection with the formation of drusen in the affected tissues - granules of tightly intertwined threads in the form of rays extending from the center and ending in flask-shaped thickenings. Actinomycetes, like fungi, form mycelium - threadlike intertwining cells (hyphae). They form a substrate mycelium, which is formed as a result of the ingrowth of cells into a nutrient medium, and an air mycelium that grows on the surface of the medium. Actinomycetes can divide by fragmentation of the mycelium into cells similar to rod-shaped and coccoid bacteria. On the aerial hyphae of actinomycetes, spores are formed that serve for reproduction. Actinomycete spores are usually not heat-resistant.
A common phylogenetic branch with actinomycetes is formed by the so-called nocardi-like (nocardioform) actinomycetes, a collecting group of rod-shaped, irregularly shaped bacteria. Their individual representatives form branching forms. These include bacteria of the genus Corynebacterium, Mycobacterium, Nocardianjxp. Nocardia-like actinomycetes are distinguished by the presence of arabinose, galactose, and also mycolic acids and large amounts of fatty acids in the cell wall. Mycolic acids and lipids of cell walls determine the acid resistance of bacteria, in particular, mycobacteria of tuberculosis and leprosy (when stained according to Ziehl-Nelsen, they are red, and non-acid-resistant bacteria and tissue elements, sputum are blue).
Pathogenic actinomycetes cause actinomycosis, nocardia - nocardiosis, mycobacteria - tuberculosis and leprosy, corynebacteria - diphtheria. Saprophytic forms of actinomycetes and nocardia-like actinomycetes are widespread in the soil, many of them are antibiotic producers.
Cell wall- a strong, elastic structure that gives bacteria a certain shape and, together with the underlying cytoplasmic membrane, "restrains" high osmotic pressure in the bacterial cell. It participates in the process of cell division and transport of metabolites, has receptors for bacteriophages, bacteriocins and various substances. The thickest cell wall in gram-positive bacteria (Fig. 2.4 and 2.5). So, if the thickness of the cell wall of gram-negative bacteria is about 15-20 nm, then in gram-positive bacteria it can reach 50 nm or more.
Mycoplasma- small bacteria (0.15-1.0 microns), surrounded only by the cytoplasmic membrane. They belong to the class Mollicutes, contain sterols. Due to the absence of a cell wall, mycoplasmas are osmotically sensitive. They have a variety of shapes: coccoid, filamentous, flask-shaped. These forms are visible during phase-contrast microscopy of pure cultures of mycoplasmas. On a dense nutrient medium, mycoplasmas form colonies resembling fried eggs: the central opaque part, immersed in the medium, and the translucent periphery in the form of a circle.
Mycoplasmas cause SARS in humans (Mycoplasma pneumoniae) and lesions of the genitourinary tract (M.homi- nis and etc.). Mycoplasmas cause diseases not only in animals, but also in plants. Non-pathogenic representatives are quite widespread.
2.2.2. Bacterial cell structure
The structure of bacteria has been well studied using electron microscopy of whole cells and their ultra-thin sections, as well as other methods. The bacterial cell is surrounded by a membrane consisting of a cell wall and a cytoplasmic membrane. Under the envelope is the protoplasm, which consists of cytoplasm with inclusions and a nucleus called the nucleoid. There are additional structures: capsule, microcapsule, mucus, flagella, pili (Fig. 2.3). Some bacteria can form spores under unfavorable conditions.
In the cell wall of gram-positive bacteria contains a small amount of polysaccharides, lipids, proteins. The main component of the cell wall of these bacteria is a multilayer peptidoglycan (mu-rein, mucopeptide), which makes up 40-90% of the cell wall mass. Teichoic acids (from the Greek. teichos - wall), the molecules of which are chains of 8-50 glycerol and ribitol residues connected by phosphate bridges. The shape and strength of bacteria is given by the rigid fibrous structure of a multilayer, cross-linked peptide-linked peptidoglycan.
Peptidoglycan is represented by parallel molecules glycan... consisting of repeating residues of N-acetylglucosamine and N-acetylmuramic acid linked by a glycosidic bond. These bonds are broken by lysozyme, which is an acetylmuramidase. Glycan molecules are linked through N-acetylmuramic acid by a cross-peptide bond of four amino acids ( tetrapeptide). Hence the name of this polymer - peptidoglycan.
The peptide bond of peptidoglycan in gram-negative bacteria is based on tetrapeptides consisting of alternating L- and D-amino acids, for example: L-alanine - D-glutamic acid - meso-diaminopimelic acid - D-alanine. Have E.coli (gram-negative bacterium) peptide chains are connected to each other through D-alanine of one chain and meso-diaminopimeli-
new acid is different. The composition and structure of the peptide part of the peptidoglycan of gram-negative bacteria are stable, in contrast to the peptidoglycan of gram-positive bacteria, the amino acids of which may differ in composition and sequence. Peptidoglycan tetrapeptides in gram-positive bacteria are connected to each other by polypeptide chains of 5 residues
glycine (pentaglycine). Instead of meso-diamino-pimelic acid, they often contain lysine. Glycan elements (acetylglucosamine and acetylmuramic acid) and tetra-peptide amino acids (meso-diaminopimelic and D-glutamic acids, D-alanine) are a distinctive feature of bacteria, since they are absent in animals and humans.
The ability of gram-positive bacteria during Gram staining to retain gentian violet in a complex with iodine (blue-violet color of bacteria) is associated with the property of multilayer peptidoglycan to interact with the dye. In addition, the subsequent treatment of the bacterial smear with alcohol causes the pores in the peptidoglycan to narrow and thereby retains the dye in the cell wall. Gram-negative bacteria, after exposure to alcohol, lose their dye, which is due to the lower amount of peptidoglycan (5-10% of the mass of the cell wall); they are discolored with alcohol and turn red when treated with fuchsin or safranin.
V cell wall composition of gram-negative bacteria enters the outer membrane, bound by lipoprotein to the underlying layer of peptidoglycan (Fig. 2.4 and 2.6). During electron microscopy of ultrathin sections of bacteria, the outer membrane looks like a wave-like three-layer structure, similar to the inner membrane, which is called cytoplasmic. The main component of these membranes is a bimolecular (double) lipid layer.
The outer membrane is a mosaic structure represented by lipopolysaccharides, phospholipids and proteins. Its inner layer is represented by phospholipids, and in the outer layer is located lipopolysaccharide(LPS). Thus, the outer membrane is asymmetrical. The LPS of the outer membrane consists of three fragments:
lipid A - a conservative structure, practically the same in gram-negative bacteria;
core, or core, crustal part (lat. core - core), relatively conserved oligosaccharide structure;
highly variable O-specific polysaccharide chain formed by repeating identical oligosaccharide sequences.
LPS is “anchored” in the outer membrane by lipid A, which determines the toxicity of L PS and is therefore identified with endotoxin. The destruction of bacteria by antibiotics releases large amounts of endotoxin, which can cause endotoxic shock in the patient. Lipid A leaves the nucleus, or the core part of the LPS. The most constant part of the LPS core is keto-deoxyoctonic acid (3-deoxy-O-man-no-2-octulosonic acid). The O-specific chain extending from the core part of the LPS molecule determines the serogroup, serovar (a type of bacteria detected by immune serum) of a particular strain of bacteria. Thus, the concept of LPS is associated with the concept of the O-antigen, by which bacteria can be differentiated. Genetic changes can lead to defects, "shortening" of bacterial LPS, and as a result of this "rough" colonies of R-forms.
Matrix proteins of the outer membrane permeate it in such a way that protein molecules called porins border hydrophilic pores through which water and small hydrophilic molecules with a relative mass of up to 700 Da pass.
Between the outer and cytoplasmic membranes is the periplasmic space, or periplasm, containing enzymes (proteases, lipases, phosphatases,
nucleases, beta-lactamases), as well as components of transport systems.
When the synthesis of the bacterial cell wall is disturbed under the influence of lysozyme, penicillin, protective factors of the body and other compounds, cells with an altered (often spherical) shape are formed: protoplasts are bacteria completely devoid of the cell wall; spheroplasts are bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, that is, acquire a full-fledged cell wall and restore their original shape.
Bacteria of the sphero- or protoplast type that have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to multiply are called L-forms (from the name of the D. Lister Institute, where they were first studied). L-forms can also arise as a result of mutations. They are osmotically sensitive, spherical, flask-shaped cells of various sizes, including those passing through bacterial filters. Some L-forms (unstable), upon removal of the factor that led to changes in bacteria, can reverse, "returning" to the original bacterial cell. L-forms can form many pathogens of infectious diseases.
Cytoplasmic membranes ana in electron microscopy of ultrathin sections, it is a three-layer membrane (2 dark layers 2.5 nm thick each are separated by a light - intermediate). In structure (see Fig. 2.5 and 2.6), it is similar to the plasmalemma of animal cells and consists of a double layer of lipids, mainly phospholipids, with embedded surface and integral proteins, as if penetrating through the membrane structure. Some of them are permeases involved in the transport of substances.
The cytoplasmic membrane is a dynamic structure with movable components, therefore it is presented as a mobile fluid structure. It surrounds the outer part of the cytoplasm of bacteria and is involved in the regulation of osmotic pressure
tion, transport of substances and energy metabolism of the cell (due to enzymes of the electron transport chain, adenosine triphosphatase, etc.).
With excessive growth (in comparison with the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complexly twisted membrane structures called mesosomes. Less intricately twisted structures are called intracytoplasmic membranes. The role of mesosomes and intracytoplasmic membranes is not fully understood. It is even assumed that they are an artifact arising after preparation (fixation) of a preparation for electron microscopy. Nevertheless, it is believed that the derivatives of the cytoplasmic membrane participate in cell division, providing energy for the synthesis of the cell wall, take part in the secretion of substances, sporulation, that is, in processes with high energy consumption.
The cytoplasm occupies the bulk of the bacterial cell and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes responsible for the synthesis (translation) of proteins.
Bacterial ribosomes have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to SOS ribosomes characteristic of eukaryotic cells. Therefore, some antibiotics, by binding to bacterial ribosomes, suppress bacterial protein synthesis without affecting protein synthesis of eukaryotic cells. Bacterial ribosomes can dissociate into two subunits - 50S and 30S. Ribosomal RNAs (rRNAs) are conservative elements of bacteria (the “molecular clock” of evolution). 16S rRNA is part of the small subunit of ribosomes, and 23S rRNA is part of the large subunit of ribosomes. The study of 16S rRNA is the basis of genosystematics, making it possible to assess the degree of kinship of organisms.
The cytoplasm contains various inclusions in the form of granules of glycogen, polysaccharides, beta-hydroxybutyric acid and polyphosphates (volutin). They accumulate when there is an excess of nutrients in the environment and
play the role of reserve substances for nutrition and energy needs.
Volutin has an affinity for the main dyes and is easily detected using special staining methods (for example, according to Neisser) in the form of metachromatic granules. With toluidine blue or methylene blue, volutin is colored red-violet, and the cytoplasm of the bacterium is blue. The characteristic arrangement of volutin granules is revealed in the diphtheria bacillus in the form of intensely staining cell poles. Metachromatic coloration of volutin is associated with a high content of polymerized inorganic polyphosphate. In electron microscopy, they look like electron-dense granules with a size of 0.1-1.0 microns.
Nucleoid- the equivalent of the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, closed in a ring and tightly packed like a ball. The nucleus of bacteria, unlike eukaryotes, does not have a nuclear envelope, nucleolus and basic proteins (histones). Usually, a bacterial cell contains one chromosome, represented by a closed ring DNA molecule. If division is disturbed, 4 or more chromosomes can converge in it. The nucleoid is detected in a light microscope after staining by DNA-specific methods: according to Fehlgen or according to Romanovsky-Giemsa. On electron diffraction patterns of ultrathin sections of bacteria, the nucleoid has the form of light zones with fibrillar, filamentous structures of DNA, connected by certain areas with
cytoplasmic membrane or meso-
mine involved in chromosome replication (see Fig. 2.5 and 2.6).
In addition to the nucleoid, represented by one
chromosome, the bacterial cell contains
non-chromosomal factors of heredity -
plasmids (see Section 5.1.2.), representing
are covalently closed DNA rings.
Capsule, microcapsule, mucus ... Capsule-
a mucous structure with a thickness of more than 0.2 microns, firmly associated with the cell wall of bacteria and having clearly defined external boundaries. The capsule is distinguishable in smears-imprints from the pathological material. In pure cultures of bacteria, the capsule is formed
less often. It is detected with special methods of staining the smear according to Burri-Hins, which create a negative contrasting of the substances of the capsule: ink creates a dark background around the capsule.
The capsule consists of polysaccharides (ec-zopolysaccharides), sometimes of polypeptides; for example, in the anthrax bacillus, it consists of polymers of D-glutamic acid. The capsule is hydrophilic and contains a large amount of water. It prevents bacterial phagocytosis. Antigen capsule: antibodies against the capsule cause it increase (reaction swollen and I capsule ly).
Many bacteria form a microcapsule - a slimy formation less than 0.2 microns thick, detected only by electron microscopy. Mucus should be distinguished from the capsule - mucoid exopolysaccharides that do not have clear external boundaries. The mucus is water soluble.
Mucoid exopolysaccharides are characteristic of mucoid strains of Pseudomonas aeruginosa, which are often found in the sputum of patients with cystic fibrosis. Bacterial exopolysaccharides are involved in adhesion (adhesion to substrates); they are also called glyco-
calyx. In addition to the synthesis of exopolysaccharides by bacteria, there is another mechanism for their formation: by the action of extracellular enzymes of bacteria on disaccharides. As a result, dextrans and levans are formed.
The capsule and mucus protect bacteria from damage, drying out, since, being hydrophilic, they bind water well, prevent the action of protective factors of the macroorganism and bacteriophages.
Flagella bacteria determine the mobility of the bacterial cell. Flagella are thin filaments originating from the cytoplasmic membrane and are longer than the cell itself (Fig. 2.7). Flagella thickness 12-20 nm, length 3-15 microns. They consist of 3 parts: a spiral filament, a hook and a basal corpuscle containing a rod with special discs (1 pair of discs for gram-positive bacteria and 2 pairs for gram-negative bacteria). The flagella are attached to the cytoplasmic membrane and cell wall by discs. This creates the effect of an electric motor with a rod - a rotor that rotates the flagellum. The difference in proton potentials across the cytoplasmic membrane is used as an energy source. The rotation mechanism is provided by proton ATP synthetase. The rotation speed of the flagellum can reach 100 r / s. If a bacterium has several flagella, they begin to rotate synchronously, intertwining into a single bundle, forming a kind of propeller.
Flagella are composed of a protein - flagellin (from. flagellum - flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are twisted in a spiral.
The number of flagella in bacteria of various species varies from one (monotrichous) in Vibrio cholerae to tens and hundreds of flagella extending along the perimeter of the bacteria (peritrichus), in E. coli, Proteus, etc. Lofotrichs have a bundle of flagella at one of the ends of the cell. Amphitrichs have one flagellum or bundle of flagella at opposite ends of the cell.
Flagella are detected using electron microscopy of preparations sprayed with heavy metals, or in a light microscope after processing by special methods based on etching and adsorption of various
substances leading to an increase in the thickness of the flagella (for example, after silvering).
Villi, or drank(fimbria) - filamentous formations (Fig. 2.7), thinner and shorter (3 + 10 nm x 0.3 + 10 microns) than flagella. Peels extend from the surface of the cell and are composed of pilin protein. They have antigenic activity. Distinguish between pills responsible for adhesion, that is, for the attachment of bacteria to the affected cell, as well as pills responsible for nutrition, water-salt metabolism, and sex (F-drank), or conjugation, drank.
Usually they drank in great numbers - several hundred per cage. However, she usually has 1-3 sex saws per cell: they are formed by the so-called "male" donor cells containing transmissible plasmids (F-, R-, Col-plasmids). A distinctive feature of genital pili is their interaction with special "male" spherical bacteriophages, which are intensively adsorbed on genital pili (Fig. 2.7).
Controversy- a peculiar form of dormant bacteria with a gram-positive type of cell wall structure (Fig. 2.8).
Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutritional deficiency, etc.). One spore (endospore) forms inside the bacterial cell. Spore formation contributes to the preservation of the species and is not a means of reproduction, as in fungi.
Spore-forming bacteria of the genus Bacillus, at which the size of the spore does not exceed the diameter of the cell are called bacilli. Spore-forming bacteria in which the size of the spore exceeds the diameter of the cell, which is why they take the shape of a spindle, are called clostridia, for example, bacteria of the genus Clostridium (lat. Clostridium - spindle). Spores are acid-resistant, therefore, they are stained according to the Aujeszky method or the Ziehl-Nelsen method in red, and the vegetative cell in blue.
Spore formation, the shape and location of spores in the cell (vegetative) are a specific property of bacteria, which makes it possible to distinguish them from each other. The shape of the spores can be oval, spherical; the location in the cell is terminal, that is, at the end of the bacillus (in the causative agent of tetanus), subterminal - closer to the end of the bacillus (in causative agents of botulism, gas gangrene) and central in the anthrax bacillus).
Process sporulation(sporulation) passes through a number of stages, during which part of the cytoplasm and the chromosome of the bacterial vegetative cell are separated, surrounded by an ingrowing cytoplasmic membrane - a prospore is formed. The prospore is surrounded by two cytoplasmic membranes, between which a thick altered peptidoglycan layer of the cortex (cortex) is formed. From the inside, it comes into contact with the cell wall of the spore, and from the outside - with the inner shell of the spore. The outer shell of the spore is formed by a vegetative cell. Spores of some bacteria have an additional cover - exosporium. Thus, a multilayer poorly permeable shell is formed. Spore formation is accompanied by intensive consumption of spore, and then the forming shell of the spore of dipicolinic acid and calcium ions. The dispute acquires heat resistance, which is associated with the presence of calcium dipicolinate in it.
The spore can persist for a long time due to the presence of a multilayer shell, calcium dipicolinate, low water content and sluggish metabolic processes. In soil, for example, the causative agents of anthrax and tetanus can persist for decades.
In favorable conditions, spores germinate, passing through three successive stages: ac-
tivation, initiation, growth. In this case, one bacterium is formed from one spore. Activation is the readiness to germinate. At a temperature of 60-80 ° C, the spore is activated for germination. Germination initiation takes several minutes. The sprouting stage is characterized by rapid growth, accompanied by the destruction of the shell and the emergence of the seedling.
Microbiology studies the structure, vital activity, living conditions and development of the smallest organisms called microbes, or microorganisms.
“Invisible, they constantly accompany a person, invading his life either as friends or as enemies,” said Academician V. L. Omelyanskiy. Indeed, microbes are everywhere: in the air, in water and in soil, in humans and animals. They can be beneficial and are used in the manufacture of many foods. They can be harmful, cause human diseases, spoilage of food, etc.
Microbes were discovered by the Dutchman A. Levenguk (1632-1723) at the end of the 17th century, when he made the first lenses with magnifications of 200 or more times. The microcosm he saw amazed him, Levenguk described and sketched the microorganisms he found on various objects. He laid the foundation for the descriptive nature of the new science. The discoveries of Louis Pasteur (1822-1895) proved that microorganisms differ not only in shape and structure, but also in their vital functions. Pasteur found that yeast causes alcoholic fermentation, and some microbes are capable of causing infectious diseases in humans and animals. Pasteur went down in history as the inventor of the method of vaccination against rabies and anthrax. The world famous contribution to microbiology R. Koch (1843-1910) - discovered the causative agents of tuberculosis and cholera, I. I. Mechnikov (1845-1916) - developed the phagocytic theory of immunity, the founder of virology D. I. Ivanovsky (1864-1920), N. F. Gamaley (1859-1940) and many other scientists.
Microbes - these are the smallest, predominantly single-celled living organisms, visible only through a microscope. The size of microorganisms is measured in micrometers - microns (1/1000 mm) and nanometers - nm (1/1000 microns).
Microbes are characterized by a huge variety of species, differing in structure, properties, and the ability to exist in various environmental conditions. They may be unicellular, multicellular and non-cellular.
Microbes are divided into bacteria, viruses and phages, fungi, yeast. Separately, varieties of bacteria are distinguished - rickettsia, mycoplasma, a special group is made up of protozoa (protozoa).
Bacteria- predominantly unicellular microorganisms ranging in size from tenths of a micrometer, for example, mycoplasma, to several micrometers, and in spirochetes - up to 500 microns.
There are three main forms of bacteria - spherical (cocci), rod-shaped (bacilli, etc.), convoluted (vibrios, spirochetes, spirilla) (Fig. 1).
Globular bacteria (cocci) are usually ball-shaped, but may be slightly oval or bean-shaped. Cocci can be located one by one (micrococci); in pairs (diplococci); in the form of chains (streptococci) or grape bunches (staphylococci), in a package (sarcins). Streptococci can cause sore throat and erysipelas, staphylococci - various inflammatory and purulent processes.
Rice. 1. Forms of bacteria: 1 - micrococci; 2 - streptococci; 3 - sardines; 4 - sticks without spores; 5 - sticks with spores (bacilli); 6 - vibrios; 7- spirochetes; 8 - spirilla (with flagella); staphylococci
Rod-shaped bacteria the most common. The rods can be single, connected in pairs (diplobacteria) or in chains (streptobacteria). Coliform bacteria include Escherichia coli, causative agents of salmonellosis, dysentery, typhoid fever, tuberculosis, etc. Some rod-shaped bacteria have the ability to form under unfavorable conditions disputes. Spore-forming rods are called bacilli. Spindle-shaped bacilli are called clostridia.
Spore formation is a complex process. Spores differ significantly from a normal bacterial cell. They have a dense shell and a very small amount of water, they do not require nutrients, and reproduction completely stops. Spores are able to withstand drying out for a long time, high and low temperatures and can be in a viable state for tens and hundreds of years (spores of anthrax, botulism, tetanus, etc.). Once in a favorable environment, the spores germinate, that is, they turn into the usual vegetative propagating form.
Curled bacteria can be in the form of a comma - vibrios, with several curls - spirilla, in the form of a thin twisted stick - spirochetes. Vibrios include the causative agent of cholera, and the causative agent of syphilis is the spirochete.
Bacterial cell has a cell wall (membrane) often covered with mucus. Mucus often forms a capsule. The contents of the cell (cytoplasm) are separated from the membrane by the cell membrane. The cytoplasm is a transparent protein mass in a colloidal state. The cytoplasm contains ribosomes, a nuclear apparatus with DNA molecules, various inclusions of reserve nutrients (glycogen, fat, etc.).
Mycoplasmas - bacteria lacking a cell wall, which need growth factors contained in yeast for their development.
Some bacteria can move. The movement is carried out with the help of flagella - thin filaments of different lengths, making rotational movements. Flagella can be in the form of a single long filament or in the form of a bundle, can be located over the entire surface of the bacterium. Many rod-shaped bacteria and almost all curved bacteria have flagella. Spherical bacteria, as a rule, do not have flagella, they are immobile.
Bacteria multiply by dividing in two. The division rate can be very high (every 15-20 minutes), while the number of bacteria increases rapidly. This rapid division is seen in foods and other nutrient-rich substrates.
Viruses- a special group of microorganisms that do not have a cellular structure. Viruses are measured in nanometers (8-150 nm), so they can only be seen with an electron microscope. Some viruses are composed only of protein and one of nucleic acids (DNA or RNA).
Viruses cause such common human diseases as influenza, viral hepatitis, measles, as well as animal diseases - foot and mouth disease, animal plague and many others.
Viruses of bacteria are called bacteriophages, fungal viruses - mycophages etc. Bacteriophages are found wherever there are microorganisms. Phages cause the death of microbial cells and can be used for the treatment and prevention of certain infectious diseases.
Mushrooms are special plant organisms that do not have chlorophyll and do not synthesize organic substances, but require ready-made organic substances. Therefore, fungi develop on a variety of nutrient-containing substrates. Some fungi are capable of causing diseases of plants (cancer and potato late blight, etc.), insects, animals and humans.
Fungal cells differ from bacterial cells by the presence of nuclei and vacuoles and are similar to plant cells. Most often they are in the form of long and branching or intertwining threads - hyphas. From hyphae it is formed mycelium, or mycelium. The mycelium can consist of cells with one or more nuclei, or be non-cellular, representing one giant multinucleated cell. Fruit bodies develop on the mycelium. The body of some fungi can consist of single cells, without the formation of mycelium (yeast, etc.).
Fungi can reproduce in different ways, including vegetatively as a result of hyphae division. Most fungi reproduce asexually and sexually through the formation of special reproduction cells - dispute. Disputes, as a rule, are able to persist for a long time in the external environment. Matured spores can be transported over considerable distances. Once in the nutrient medium, the spores quickly develop into hyphae.
An extensive group of fungi is represented by molds (Fig. 2). Widespread in nature, they can grow on food, forming well-visible plaques of various colors. Food spoilage is often caused by mucor mushrooms, which form a fluffy white or gray mass. Rhizopus mucor mushroom causes "soft rot" of vegetables and berries, and Botrytis mushroom covers and softens apples, pears and berries. Mushrooms from the genus peniiillium can be causative agents of mold on food.
Certain types of mushrooms can not only lead to food spoilage, but also produce substances toxic to humans - mycotoxins. These include some types of fungi of the genus Aspergillus, genus Fusarium, etc.
The beneficial properties of certain types of mushrooms are used in the food and pharmaceutical industries and other industries. For example, mushrooms of the genus peniillium are used to obtain the antibiotic penicillin and in the production of cheeses (Roquefort and Camembert), mushrooms of the genus Aspergillus are used in the production of citric acid and many enzyme preparations.
Actinomycetes- microorganisms with signs of both bacteria and fungi. In terms of structure and biochemical properties, actinomycetes are similar to bacteria, and in terms of reproduction, the ability to form hyphae and mycelium, they are similar to fungi.
Rice. 2. Types of molds: 1 - peniiillium; 2- aspergillus; 3 - mucor.
Yeast- unicellular immobile microorganisms no more than 10-15 microns in size. The shape of the yeast cell is more often round or oval, less often rod-shaped, sickle-shaped or lemon-like. Yeast cells are similar in structure to fungi, they also have a nucleus and vacuoles. Yeast propagates by budding, division, or spores.
Yeast is widespread in nature, it can be found in soil and plants, food and various industrial waste containing sugar. The development of yeast in food can spoil it by fermenting or souring. Some yeasts have the ability to convert sugar into ethyl alcohol and carbon dioxide. This process is called alcoholic fermentation and is widely used in the food and wine industries.
Some types of candida yeast cause human disease - candidiasis.
THEME 2
MICROORGANISMS
2.1. Microorganism morphology
The study of the morphology of microorganisms is impossible without magnifying devices - microscopes. The first magnifying device was made in 1608 by the Italian scientist G. Galilei, who made a long tube (like a modern telescope) with two magnifying lenses inside and with its help looked at distant objects. Then he improved this device and in 1610 made the first "microscope" with which he looked at small objects.
In 1625, the German scientist Johann Faber called Galileo's second device a microscope.
In 1665 the English scientist Robert Hooke improved the microscope by adding a third collecting lens.
In 1667 the Italian scientist Eustachius Davini made the 2nd lens eyepiece, which resulted in a flat visible field.
In 1715, the German scientist Gertel first used an illuminating mirror to direct rays of color towards an object and a lens.
In 1850 the Italian scientist D. Amiga created an immersion microscope and used water immersion, and in 1878 the English scientist V. Stephansson proposed oil immersion.
1886 German scientist F. Ebner made a dark-field microscope.
In 1908 German scientists A. Köhler and G. Zidontonf created a luminescent microscope.
In 1930 E. Ruska, M. Knoll and B, Borrie created the first electron microscope.
2.1.2 Morphology and structure of bacteria
The shape and size of bacteria
According to their external shape, bacteria can be divided into several groups: spherical (spherical), rod-shaped, twisted, vibrios, ring-shaped, (toroids) in the shape of a hexagonal star, bacteria forming outgrowths (protrusions), worm-shaped and branched bacteria. However, most of the known bacteria are spherical, rod-shaped, and crimped in shape.
Spherical bacteria or cocci have a diameter of 1-2 microns (micrometer). Depending on the location of the cells after division, they are subdivided into a number of groups. If after division the cells are arranged singly, then they are called monococci or micrococci. If division occurs in one plane and the cells do not separate, but remain connected in two, then they are called diplococci. After such a division, if the cells do not separate and form chains of different lengths, then they are called streptococci. The division of cocci in two mutually perpendicular splashes leads to the formation of forms of four tetracoccal cells. With the simultaneous division of cocci in three mutually perpendicular planes, packets of eight cells are formed in the form of a cube. Such an accumulation of cocci is called sarcinum. When cocci divide unevenly in several planes, clusters of cells appear that resemble bunches of grapes. These are staphylococci.
Among the cocci there are representatives with an irregularly round cell shape. These include pneumococci, meningococci, and gonococci. The form of pneumococci is oval, reminiscent of a candle flame, the cells are connected in pairs by wide bases. Meningococci and gonococci are in the form of beans or coffee beans, the cells are connected on two concave sides.
Coccal forms, with the exception of Sarsina ureae (urinary sarcina), do not form spores, are immobile, and are widespread in nature. Many of the cocci are pathogenic pathogens of inflammatory processes, for example, pneumococci, meningococci, pyogenic streptococci and staphylococci; others are non-pathogenic, causative agents of lactic acid fermentation, for example, Streptococcus lactis, Str.cremoris; some are used in production for the biosynthesis of dextran, a plasma substitute for Leuconostos mesenteroides.
The smallest bacteria are found among the spherical forms that belong to mycoplasmas. Mycoplasmas with
cell diameter 0.12-0.15 microns.
The most numerous group of bacteria belongs to the rod-shaped forms. The cells are cylindrical in shape, their ends can be round or cut, straight and convex. There are short and long sticks, thick and thin sticks. The size of bacillus-like bacteria is from a few tenths of a micron to 100 and more. In short rods, the length of the lines is not much longer than the diameter of the cell, so that sometimes it is rather difficult to distinguish them from cocci.
In some bacteria, rod-shaped cells combine into long filaments to form what are called filamentous forms. These multicellular filamentous forms include some iron bacteria and colorless sulfur bacteria. The length of the filament of the sulfur bacteria Beggiatoa mirabilis reaches 1 cm or more. She is considered a giant among bacteria.
According to their ability to sporulate, rod-shaped forms are divided into two groups: bacteria and bacilli. Cells that do not form spores are called bacteria. They are usually located singly. In the overwhelming majority, these are small sticks belonging to the genera Bacterium and Pseudomonas. Rod-shaped forms that form spores are called bacilli (Bacillus). They differ in cell shape, due to the size and location of the spores.
If the spore is located in the center of the cell and its diameter does not exceed the diameter of the cell, then this type is called the actual bacillus; if the diameter of the spore exceeds the diameter of the cell, then when the spore is located in the center of the cell, it has a fusiform thickening and is called clostridium (for example, in Clostridium pasterianum), and when the spore is located at the end, it takes the form of a drum stick or a tennis racket and is called plectridium. Spore-bearing forms form long chains of cells, the so-called streptobacilli (for example, Bacillus mycoides).
Spiral microorganisms differ in the number of turns. If bacteria have cells with several large curls, then they are called spirillae. Cells with many small spiral turns are called spirochetes. Bacteria curved in the shape of a crescent or busy are called vibrios. Most of the convoluted forms are represented by trefoil species (for example, Vibrio cholerae, the causative agent of syphilis). Among them there are saprophytes living in soil and water. Crimped forms have very different cell sizes - from small 1.5-2.0 microns (vibrios) to very large 2-3 x 15-20 microns (for example, Spirillum volutans). There are organisms among prokaryotes that differ from the basic forms described above. Some bacteria have the form of a ring, closed or open, depending on the stage of growth (for example, bacteria of the genus Microcyclus). It was proposed to call such cells theroids.
In bacteria, mainly reproducing by budding, the formation of cell outgrowths is described, the number of which can range from 1 to 8 or more. The bacteria that form the outgrowths are called prostheses.
Worm-shaped bacteria (long cells with curved, very thin ends) and resembling a regular hexagonal star in appearance were isolated from natural substrates.
Some groups of prokaryotes are characterized by weak branching, for example, in mycobacteria and propionic bacteria. Some bacteria have well-defined branching. They are called actinomycetes (streptomycetes).
Bacteria with morphological variability (bremorphism) are described, for example, bacteria belonging to the group of corynebacteria, depending on conditions, can have the form of rods, cocci, or weakly branching forms.
The cell shape of prokaryotes (bacteria) is determined by a rigid (rigid) cell wall. It is the latter that gives the cell a definite, hereditarily fixed external form. In a number of bacteria (for example, in spirochetes, myxobacteria and flexibacteria), the cell wall is rather elastic, so they are able to reduce the shape of cells within certain limits, for example, by bending. Finally, bacteria are known in which the cell wall is completely absent. These are mycoplasmas and L-forms. Mycoplasmas exist in nature and are mostly pathogenic for humans and animals. L - forms are obtained experimentally under the action of chemicals that destroy the bacterial cell wall or suppress the synthesis of cell wall components. These bacteria are characterized by a pronounced bremorphism.
Structures located outside the cytoplasmic membrane (cell wall, capsule, mucous membrane, flagella, villi) are usually called surface structures or bacterial membrane. The cytoplasmic membrane, together with the cytoplasm, is called the protoplast. Let us first consider the structure, chemical composition and functions of cell surface structures.
Flagella... On the surface of the cells of many bacteria, there are structures that determine the ability of cells to move. These are flagella. Their presence, number, size, location are characteristics that are constant for a certain type of bacteria and therefore have important taxonomic significance.
If the flagella are at the poles of the cell, they speak of their polar location, if along the lateral surface of the cell, they speak of their lateral location. If one flagellum is attached to one of the poles of the cell, it is called monotrichs. If at each pole there is one or a bundle of flagella, they are called amphitrichs (or biopolar polytrichs). If the bundle of flagella is located at one of the poles of the cell -
called lofotrichs (or monopolar polytrichs). If numerous flagella are located over the entire surface of the cell, they are called peritrichous. Flagella thickness 100 - 300 A, length from 3 to 12 microns. They consist of one type of protein - flagellin.
The movement of bacteria is carried out by active rotational movements of the flagella. Some bacteria that do not have a flagellum move along a solid substrate by sliding (for example, myxobacteria, flexibacteria, spirochetes, cyanobacteria).
It should be noted that the mechanisms of movement of bacteria have not yet been clarified.
Motile bacteria move actively and in a targeted manner. Such directed movements of bacteria are called taxis. It is known chemotaxis, aerotaxis and phototaxis. The speed of movement of bacteria is high - in 1 second they can cover a distance 20 - 50 times greater than the length of the cells.
Flagella and villi are not an obligatory cellular structure, since without them bacteria also grow and multiply well.
Capsules and mucous covers... Outside, the cell wall of bacteria and cyanobacteria is often surrounded by a mucous substance. Depending on its thickness and consistency, macro and microcapsules are distinguished. A capsule is understood as a mucous formation that envelops the cell wall and has a well-defined surface. If the mucous substance surrounding the cell has an amorphous, structureless appearance and is easily separated from the surface of the prokaryotic cell, one speaks of the mucous sheath surrounding the cell. Colonies consisting of cells surrounded by a capsule have a smooth surface. They are designated as S - colonies (from the English word smooth). Colonies formed from capsule-free cells have a rough surface and are called R - colonies (from the English word rough).
Cell wall... The cell wall is an important and obligatory structural element of the prokaryotic cell (with the exception of mycoplasmas). The share of the cell wall in prokaryotic microorganisms accounts for 5 to 50% of the dry matter of the cell. It serves as a mechanical barrier between the protoplast and the external environment and gives the cells a certain shape. The cell wall protects the cell from the penetration of excess water by purely mechanical means.
The chemical composition and structure of the cell wall are constant for a particular species and are an important diagnostic feature. Depending on the structure of the cell walls, bacteria are divided into two large groups: gram-positive and gram-negative. It was found that when fixed cells of microorganisms are treated first with crystal violet and then with iodine, a colored complex is formed. With the subsequent treatment with alcohol, depending on the structure of the cell wall, the fate of the complex will be different. In gram-positive bacteria, this complex is retained by the cell, and the latter remain stained, while in gram-negative bacteria, on the contrary, the colored complex is washed out of the cells, and they become discolored. This staining method was first proposed in 1884 by the Danish scientist H. Gram.
The cell walls of gram-positive and gram-negative bacteria differ in chemical composition. It is believed that glycopeptides form a rigid cell wall scaffold. In gram-positive bacteria, they constitute the bulk of it (up to 90%), and in gram-negative bacteria, their content is much less (5-10%).
The cell wall of gram-positive bacteria contains glycopeptides (murein complex), polysaccharides, teichoic acids, lipids. The cell wall of gram-negative bacteria contains polysaccharides, lipids (up to 90%), proteins, lipopolysaccharides, lipoproteins and glycopeptides. Consequently, teichoic acids are absent in gram-negative bacteria and lipopolysaccharides and lipoproteins are absent in
gram-positive bacteria.
Cytoplasmic membrane. The contents of the cell are separated from the cell wall by the cytoplasmic membrane (CPM). Violation of the integrity of the CPM leads to the loss of cell viability. CPM is a protein-lipid complex, in which proteins make up 50-70%, lipids from 15-30%. Under an electron microscope, it is visible as a three-layer structure. According to the model proposed by G. Dawson and D. Danielli, the CPM is built of two protein layers, between which there is a lipid layer.
The MTC has a variety of functions. Membrane preparations have ATP-ase activity, catalyze the processes of synthesis of substances that make up the cell wall and mucous membrane. Oxidative enzymes are localized in the membranes. It also contains enzymes - permeases, which carry out active two-way selective transfer of various organic and inorganic substances across the membrane. There is a space between the CPM and the cell wall, which is called the periplasmic space. Many extracellular enzymes function in this space.
Cytoplasm. The contained cells surrounded by the CPM are called cytoplasm. The cytoplasm of bacteria contains nuclear material and various inclusions.
The nuclear material of bacteria, consisting of DNA, is diffusionally located in the central part of the cytoplasm and is not limited from the cytoplasm by a membrane. It is called a nucleoid.
In the cytoplasm there are membrane structures - mesosomes, in photosynthetic bacteria - tylocoids and chromatophores.
Tylocoids and chromatophores of photosynthetic bacteria are the site of localization of photosynthetic pigments.
Mesosomes differ in size, shape, and location in the cell. There are three main types of mesosomes: lamellar (lamellar), vesicular (vesicular) and tubular (tubular). They are believed to be involved in important processes of cellular metabolicism. However, the true function of bacterial mesosomes remains mysterious.
Ribosomes in a bacterial cell can exist freely in the cytoplasm or be associated with membrane structures. Protein synthesis involves ribosomal aggregates called polyrobosomes, or polysomes.
In the cytoplasm of various bacteria, solid, liquid, gaseous substances are also found.
2.1.3. Classification of bacteria
Currently, the bacterial kingdom is divided into 4 categories:
1. Gram-negative eubacteria with cell walls;
2. Gram-positive eubacteria with cell walls;
3. Eubacteria devoid of cell walls;
4. Archeobacteria.
The first category has 16 groups; the second category has 13 groups, the third category has one group, and the fourth category has 5 groups. (for more details see: 1) Bergey's Guide to Bacteria. M .: Mir, 1997, volume 1, 430 p .; 2) Schlegel. General microbiology. M .: Mir, 1987, 562 p.).
Mushrooms are eukaryotic microorganisms. They are all heterotrophs and mostly aerobes. The body of most mushrooms is made up of thin filaments-hyphae, and the plexus they form is called mycelium or mycelium. The hyphae of some fungi are divided into cells (septate) by gaems, such fungi are called multicellular. The hyphae of other fungi do not have septa - they are unicellular fungi. There are also spherical or ovoid unicellular fungi called yeast.
The structure of fungal cells differs little from the structure of cells of other equariotic organisms. Cells consist of a cell membrane, cytoplasm and one, two or more nuclei. The cytoplasm contains intracellular organelles, vacuoles and various inclusions. The cell membrane consists of a cell wall and a cytoplasmic membrane.
According to the modern system, the kingdom of fungi is divided into 8 divisions: 1) the Myxomycota division; 2) Plazmodiophoramycota department; 3) Oomycota department; 4) department
Chytridiomycota; 5) Zygomycota department; 6) Ascomycota department; 7) Department of Basidiomycota; 8) Deuteromycota department. Departments are subdivided into orders, orders - into classes, classes - into families, and families - into genera (for more details see: 1) Garibova L.V., Lekomtseva S.N. Fundamentals of mycology. M. 2005; 2) Müller E.; Leffler V. Mycology, Moscow: Mir, 1995).
Literature
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3. Schlegel G. General microbiology. Moscow: Mir, 1987.
4. Daraselia G.Ya. Microbiology, food hygiene and safety, Tbilisi, 2006.
5. Biryuzova V.I. Membrane structures of microorganisms. Moscow: Nauka, 1973.
6. Feofilova EP Cell wall of fungi. Moscow: Nauka, 1983.
