Bacteria in the process of evolution adapted to survive in the most adverse environmental conditions and retained hereditary information through the formation of spores. Bacterial spores form inside the cell. The whole process of germination (sporulation) lasts 18 - 20 hours. During this process, the bacterial cell changes whole line biochemical processes. Bacteria can remain in a spore-like state for a long time - hundreds of years. Under favorable environmental conditions, spores germinate. The germination process lasts 4-5 hours.
Sporulation occurs when:
- the nutrient substrate is depleted,
- there is a lack of carbon and nitrogen,
- accumulates in the internal environment of the cell potassium and manganese ions,
- the level of acidity of the environment changes, etc.
Rice. 1. In the photo of a spore inside a bacterial cell (the photo was taken in the light of an electron microscope - EM).
Which bacteria are capable of sporulation
Rod-shaped bacteria that form spores are called bacilli. They belong to the family Bacillaceae and are represented by the Clostridium genus Clostricdium, the Bacillus genus, and the Desulfotomaculum genus. They are all gram positive anaerobic bacteria.
Genus Clostridium contains more than 93 types of bacteria. All of them form disputes. Clostridium species cause pulmonary gangrene, are the culprits of complications after abortion and childbirth, severe toxic infections, including botulism. Spores of bacteria of this species exceed the diameter of the vegetative cell.
Genus bacillus has more than 217 species of bacteria. Pathogenic bacteria of the genus Bacillus cause a number of diseases in humans and animals, including food poisoning and anthrax. Spores of bacteria of this species do not exceed the diameter of the vegetative cell.
Rice. 2. In the photo, bacteria of the genus Clostridium. Left: Clostridia perfingens. They are the causative agents of food poisoning and gas gangrene. Right: Clostridium botulinum. Bacteria cause severe food poisoning - botulism.
Rice. 3. In the photo, the pathogen anthrax. Bacillus anthracis genus Bacillus is a large, immobile, stub-ended bacterium (left) and a spore-like bacterium (right).
Sporulation in bacteria
Preparatory stage
Before the formation of the spore itself in the vegetative bacterial cell, the level of metabolism decreases, DNA replication stops, one of the nucleotides is localized in the sporogenous zone, and dipicolinic acid begins to be synthesized.
Formation of the sporogenous zone
The formation of the sporogenous zone begins with the compaction of the cytoplasmic region in which the nucleotide is located ( prospore). The isolation of the sporogenous zone occurs with the help of cytoplasmic membrane, which begins to grow into the cell.
Prospore and spore formation
A cortex is formed between the inner and outer layers of the membrane. One of its components is dipicolinic acid, which determines the heat resistance of the spore.
The side of the membrane facing outward is covered with a shell (exospore). It consists of proteins, lipids and other compounds that are not found in a vegetative cell. The shell is thick and loose. Possesses hydrophobicity.
Spore maturation
During the period of spore maturation, the formation of all its structures ends. The spore becomes heat resistant. It takes a certain form and occupies a special position in the cell. After full maturation of the spore, autolysis of the cell occurs.
Rice. 4. The photo shows the formed spore, along the periphery of which there are remnants of the cytoplasm.
Rice. 5. The photo on the left shows a newly formed spore (A), along the periphery of which there are remnants of the cytoplasm. The cytoplasm then dies. In the photo on the right (B) is a spore purified in the laboratory.
Rice. 6. In the photo above, the stage of sporulation is from the formation of the sporogenous zone to the complete formation and lysis of cell residues. In the photo below, a dispute with ribbon-like outgrowths. O is its outer shell, K is the cortex, C is the inner part.
cortex
The cortex protects the spore from enzymes that are produced in large quantities by the cell at the final stage of sporulation. Their purpose is to completely destroy the maternal vegetative cell. In the absence of a cortex, bacterial spores are lysed. Cortex contains diaminopimelic acid, which provides thermal stability
The inner side of the cortex is adjacent to the inner side of the cytoplasmic membrane. During spore germination, the cortex transforms into the cell wall of the vegetative cell.
Spore shell (exosporium)
The side of the cytoplasmic membrane, facing outward, is covered with a shell (exospore) during spore formation. It consists of proteins, lipids and other compounds that are not found in a vegetative cell. The shell is thick and loose. It makes up about 50% of the volume of the spore itself. Possesses hydrophobicity. The outer wall of the spore is resistant to enzymes. It prevents the spore from premature germination.
Rice. 7. In the photo of a dispute with outgrowths. Its core is a resting vegetative cell.
Outgrowths on spores
On some spores, outgrowths are formed in the process of spore formation. They are varied and specific. This feature for each bacterium is hereditarily fixed and constant. Outgrowths on spores consist mainly of protein. The amino acids of the protein are similar to those of keratin and collagen. The function of outgrowths on spores has not yet been finally elucidated.
Rice. 8. Types of outgrowths on spores: flagella, tubes, ruff-shaped sticks, wide ribbons, spikes, pins, in the form of deer antlers.
Rice. 9. In the photo, spores of bacteria of the genus Clostridium. Outgrowths in the form of tubes (1 and 5), outgrowths in the form of flagella (2), ribbon-like outgrowths (3), pinnate outgrowths (4), spores, on the surface of which there are spikes (6).
Characterization of bacterial spores
In a cell that is in a spore-like state, it is noted:
- complete repression of the genome,
- almost complete lack of metabolism,
- a decrease in the amount of water in the cytoplasm by 50% (a significant loss of water by the cell leads to its death),
- increased amount of calcium and magnesium cations in the cytoplasm,
- the appearance of dipicolinic acid and cortex responsible for thermal stability,
- increase in the amount of cysteine protein and hydrophobic amino acids,
- remains viable for hundreds of years.
Spore persistence
In the process of spore formation, the spore is covered with shells - the outer shell and the cortex. They protect the spore from adverse environmental conditions.
cortex contains diaminopimelic acid, which is responsible for thermal stability. Outer shell protects the spore from premature germination and negative environmental factors.
In the spore-like state, the bacterium is resistant to elevated ambient temperatures and drying. It is able to survive in solutions with a high salt content, endure prolonged boiling and freezing, radiation and vacuum, and ultraviolet irradiation. The spore is resistant to a range of toxic substances and disinfectants.
Stability of spores of pathogenic bacteria in external environment contributes to the preservation of infection and the development of severe infectious diseases.
Type, shape and location of spores in bacteria
Bacterial spores are oval and spherical in shape. They can be located at the ends of the cell (causative agents of tetanus), closer to the center (causative agents of botulism and gas gangrene), or in the central part of the cell (anthrax bacillus). Less commonly, bacterial spores are located laterally.
Rice. 10. The photo shows terminal endospores of C. difficile and Clostridium tetani.
Rice. 11. The photo shows centrally located spores of Bacillus cereus bacteria.
Rice. 12. In the photo, the terminal location of the spore in the bacterium Bacillus subtilis.
Spore caps
On spores of the genus Clostridium and Bacillus, caps are formed in the process of spore formation. They have a conical or crescent shape and a cellular structure. The cells resemble sacs that are filled with a gaseous substance. They are in the form of sticks or ovals. The cells help the spore stay buoyant in the water. Even with centrifugation, capped spores cannot be settled. Caps on spores are formed in soil bacteria of hydromorphic soils that have formed under conditions of stagnant surface water or in the presence of groundwater.
Rice. 13. In the photo, caps on spores are cone-shaped (left) and crescent-shaped (right).
Rice. 14. In the photo, the structure of the bacterial spore cap. Individual gas cells (vacuoles, sacs) of an oval shape are visible.
DISPUTES(Greek spora sowing, sowing) - microscopic rudiments formed by certain plants and bacteria during asexual reproduction.
plant spores
C. form plants of various systematic groups - algae, fungi, many types of higher plants.
Bibliography: Willy K.A. and Dethier W.J. Biology ( Biological processes and laws), trans. from English, p. 267, 660, Moscow, 1974; Plant Life, ed. A. A. Fedorova, vol. 1 - 4, M., 1974 - 1978; Korn M. Ya. and Solov y-e in H. N. On the use of phase-contrast microscopy to observe spores in stained smears, Laborat. case, no. 6, p. 51, 1961; Brief determinant of Bergi bacteria, ed. J. Holt, trans. from English, p. 286, M., 1980; Work n about in and I. L. General microbiology, p. 65, Moscow, 1966; Guidelines for microbiological diagnosis of infectious diseases, ed. K. I. Matveeva, p. 27, M., 1973; Steinier R., Edelberg E. and Ingram J. World of microbes, trans. from English, vol. 3, p. 184, M., 1979; The bacterial spore, ed. by G. W. Gould a. A. Hurst, L.-N. Y., 1969.
T. V. Veshchikova; M. Ya. Korn (bact.); M. Ya. Korn and M. F. Kultaev (printing. Fig.).
controversy is a form of dormant Gram-positive bacteria. Spores are formed under unfavorable conditions for the existence of bacteria (drying, nutrient deficiency, etc.). In this case, one spore is formed inside one bacterium. The formation of spores contributes to the preservation of the species and is not a method of reproduction. Spore-forming rod-shaped aerobic bacteria, in which the spore size does not exceed the diameter of the cell, are called bacilli. Spore-forming rod-shaped anaerobic bacteria, in which the spore size exceeds the size of a bacterial cell, are called clostridia.
Spore formation scheme (according to G. Schlegel). A and B - formation of a septum. (c and d) environment of the spore protoplast by the mother cell membrane. E - formation of the cortex and spore membranes. E - scheme of the structure of a mature spore: 1 - cytoplasm with a nucleoid; 2 - CM spores; 3 - spore cell wall; 4 - cortex; 5 - inner shell of the spore; 6 - outer shell of the spore; 7 - exosporium.
The process of sporulation(sporulation) goes through a series of stages. First, at one of the poles of the bacterial cell, the nucleoid condenses and separates due to the formation of a septum. Then the CPM begins to overgrow the formed spore protoplast and a fold appears, consisting of two layers of the CPM, later they merge, as a result of which the formed prespore is surrounded by a double membrane. Between the membranes facing each other, the germinal wall, the cortex, as well as the outer and inner membranes located outside the membranes, are formed.
When unfavorable conditions occur for bacteria, they are able to form spores. Unfavorable conditions may be the lack of nutrients in the medium, changes in its acidity, high or low temperatures, drying out of the medium, and more.
The formation of spores by bacteria is primarily a way to survive adverse environmental conditions. Unlike other organisms, bacteria rarely use sporulation for reproduction.
Bacterial spores remain viable under very adverse environmental conditions. They are able to survive extremely high and low temperatures and remain viable for many years. This is how bacteria are known, the spores of which can germinate after 1000 years. In other bacteria, spores can withstand boiling. It happens that spores are able to survive temperatures below -200 degrees Celsius.
In those days when life on Earth had just appeared, and only bacteria existed on it, perhaps the weather conditions could change quickly, become very severe. In order to survive, bacteria have evolved the ability to sporulate. Today, bacteria can live where other organisms cannot survive.
In bacterial spores, all life processes are almost stopped, there is little cytoplasm, and it is dense. The spore is covered with a thick shell that protects it from destructive environmental factors. However, the spore contains everything necessary (including bacterial DNA) to germinate under favorable conditions and form a full-fledged bacterial cell.
Most bacteria form spores, which are called endospores. They are mainly formed by rod-shaped bacteria. "Endo" means "within". That is, in most bacteria, spores are formed inside the cell. When spores are formed, the cell membrane is invaginated, and an area is isolated inside the bacterium - the future spore. That's where the DNA goes. Around this area, a thick layer of the so-called bark will form, which will protect the spore. There is a membrane on its inner and outer sides. On the outside of the membrane there are several more shells.
In rod-shaped bacteria, endospores can form in different places in the cell. For some - in the middle, for others - closer to the end, for others - at the very edge of the rod-cell.
There are types of bacteria that do not form endospores, but exospores, cysts and other forms of dormant forms. "Exo" says that the spore is not formed inside the bacterial cell, but, as it were, outside of it. The formation of exospores occurs by the formation of peculiar buds in the cell. After that, such kidneys are covered with a thick shell, turn into spores and separate.
With the help of spores, bacteria not only survive adverse conditions, but also settle, since spores are very light and are easily carried by wind and water.
Answer options for your crossword puzzle
BACILLA
CLOSTRIDIA
- Genus of rod-shaped bacteria that produce spores
BACILLUS
COCCOBACTERIA
- Bacterium in the form of a short thick rod or slightly elongated coccus
- Bacteria in the form of a short thick rod
BACTEROIDS
MYCOPLASMA
ANTIBIOGRAM
- The result of determining the sensitivity spectrum of the studied bacterial culture to various antibiotics, expressed in tabular or textual form
BARREL
HYMENOPHORE
- The underside of the mushroom cap that produces spores
- The surface of the fruiting bodies of fungi, mainly basidiomycetes, on which hymenium develops, bearing basidia with spores
DISCUSSION
These words were also found by queries:
There are some types of bacteria that produce round or oval bodies, which are characterized by strong light refraction.
These formations are called endospores. Sporulation is one of the stages of the development cycle of certain microorganisms in response to the adverse effects of the external environment, developed in the process of evolution in the struggle for the preservation of the species.
The lack of nutrients causes various reactions in some microorganisms that prepare the cell for a long period during which nutrients are not available. The transition to sporulation is observed when the nutrient substrate is depleted, with a lack of carbon, nitrogen or phosphorus, a change in the pH of the medium, etc.
Spore formation is inherent mainly in rod-shaped microorganisms (bacilli and clostridia, and relatively rarely observed in cocci (Sarcina urea, Sarcina lutea) and convoluted forms (Desulfovibrio desulfuricans).
Sporulation occurs in the external environment, on nutrient media and is not observed in human and animal tissues.
The process of spore formation is divided into seven successive stages, characterized by various cytological changes (Fig.
spore-forming bacteria
Preparatory stages(stages 0 and I). At these stages, there are still no morphologically visible changes in the cell, but the amount of water decreases and the cytoplasm becomes denser.
Prospore stage(stage II) is the first stage of sporulation recognizable morphologically.
It is characterized by the appearance of a prospore septum, which divides the cell into a small prospore and a large mother cell. This is the key stage of sporulation.
During prospore absorption stages(stage III) there is a spatial separation of a small prospore, which passes into the cytoplasm of the mother cell.
Outside the prospore, a double membrane structure is formed.
Prespore stage characterized by the formation of a cortex (a dense spore membrane) inside the membrane structure of the prospore (stage IV) and the condensation of proteins on its surface (stage V).
On the ripening stages(stage VI) the spore coat develops further and becomes resistant to chemical agents and heat. The formed spore occupies approximately 1/10 of the mother cell.
The final stage is mature spore release from the mother cell (stage VII).
The process of spore formation proceeds within 18-20 hours.
Due to the presence of a dense multilayer shell with a lamellar structure, a minimum amount of water and a high content of calcium, lipids and dipicolinic acid, spores are highly resistant to environmental factors and disinfectants. They withstand relatively high and low temperatures, prolonged drying, exposure to radiation, toxic substances, etc.
They can survive for decades under adverse conditions.
Once in favorable conditions, spores germinate and again turn into vegetative forms.
The process of spore germination begins with the absorption of water. They swell, increase in size. From the shell on the pole, in the center or between the pole and the center, a process appears, from which the stick is pulled out. The process of spore germination is much faster and takes 4-5 hours.
By the nature of localization in the body of microorganisms, spores are located:
Central (anthrax stick, anthracoid stick, etc.).
2. Subterminally - closer to the end (the causative agent of botulism, etc.).
3. Terminal - at the end of the stick (the causative agent of tetanus).
In some species of spore-forming microorganisms, the diameter of the spores exceeds the diameter of the bacterial cell. If spores are localized subterminally, such bacteria take the form of a spindle. These include clostridia of butyric fermentation. In some clostridia, for example, in the causative agent of tetanus, spores are located terminally, their cell resembles a drumstick (Fig.
Rice. 13. Shapes and location of spores in bacilli.
The ability to spore formation is used in the systematics of microbes, as well as in the choice of methods for disinfecting objects, premises, food products, various products.
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Some bacteria have the ability to form spores. This applies primarily to rod-shaped forms; in cocci, sporulation is rare, but for vibrio and spirilla it is absent. The process of sporulation consists in the fact that in a certain place of the bacterial cell, the cytoplasm begins to thicken, then this area is covered with a rather dense shell. The rest of the cell is gradually destroyed. Thus, the bacterial cell turns into a spore within a few hours.
In a bacterial cell, the spore can be located centrally, at the end, or occupy an intermediate position (subterminal).
controversy various kinds have a different shape. They can be spherical, oval. Sometimes the diameter of the spores exceeds the thickness of the cell, and this leads to its deformation - swelling.
These features of sporulation in various bacteria are fairly constant features and are often used in diagnostics, i.e.
e. when recognizing bacteria. Sporulation is stimulated by the onset of unfavorable conditions for development, depletion of the nutrient medium.
The life processes of an exchange nature, for example, respiration, although they occur in disputes, are extremely slow.
Spores are more resistant than vegetative forms of the same bacteria to the action of penetrating radiation, ultrasound, drying, freezing, rarefaction, hydrostatic pressure, the action of toxic substances, etc.
Spores of some bacteria remain viable even after being in boiling concentrated acid for 20 minutes.
The resistance of spores increases with their preliminary dehydration.
The heat resistance of spores can be explained by the relatively low content of free water in the cytoplasm (according to some data, only 40%) and the relatively high content of dry matter (mainly protein).
A dense, multi-layered shell protects spores well from the penetration of harmful substances.
Due to the ability to form spores, which have an exceptionally high resistance to external influences, spore-forming bacteria remain viable under extremely unfavorable conditions.
Suppression of viability and destruction of spore-forming bacteria is one of the main practical tasks of the canning industry, processing and storage of agricultural products.
Spores are a special, stable form of existence of bacteria that contributes to the conservation of this species.
Sporulation in bacteria is not associated with reproduction, since a bacterial cell is able to form only one spore.
If the spores fall into favorable conditions, each of them turns into a normal (vegetative) bacterial cell within a few hours.
First, the spore shell bursts, and then a cell germ appears in this place, gradually turning into a normal cell. Germination takes several hours. In practice, it is often necessary to observe the so-called "dormant" disputes. These are those that lag behind the general mass in the rate of germination and, while remaining viable for a long time, can germinate gradually over long periods ranging from several days to many years.
The ability to form spores is taken into account in the taxonomy of bacteria, when choosing methods for sterilizing food products, equipment, and inventory.
Sporulation can be lost with frequent subcultures of bacteria on a fresh medium, cultivating them at high temperatures.
Reproduction of bacteria
There are many methods of reproduction observed in various bacteria.
In the vast majority of representatives of this group of microorganisms, reproduction is carried out by dividing cells into two parts.
In the middle part of a cell physiologically prepared for reproduction, a transverse septum is formed due to the invagination of the cytoplasmic membrane.
Splitting, it divides the cell into two halves. The resulting new cells may be somewhat unequal in size, since the septum does not always run in the middle of the mother cell.
Cocci in the process of reproduction sequentially divide into one, two or three mutually perpendicular planes. After division, they remain more or less bonded to each other, resulting in combinations of cocci that differ in mutual arrangement (see Fig.
rice. 1): diplococci - paired cocci; streptococci - chains of cocci; tetracocci - four cocci; sarcins - in the form of regular bundles of 8, 16 pieces; staphylococci - clusters resembling bunches of grapes. With a very weak connection or its absence between the cells that arise during division, micrococci are formed, in the mutual arrangement of which there are no regularities. They are located singly or in the form of random clusters of several copies.
Rods (bacteria, bacilli), like cocci, can be arranged in pairs along the length - diplobacteria and in chains - streptobacteria.
Most of the sticks are located singly, randomly. According to the external outlines, individual representatives of the rod-shaped ones differ markedly from each other. There are sticks of a strictly cylindrical shape, barrel-shaped, with sharply chopped off, concave or pointed ends, etc.
Reproduction by division is not limited to doubling the number of cells.
The structural elements and substances of the mother cell are also redistributed between the emerging new cells. Most of the cells of the new generation inherit the defect-free structures of the parent organisms, the second - less complete. In connection with this distribution, after several cycles of division, a certain amount of non-viable cells is formed. It has been established that the proportion of such cells per each cycle of division is approximately 10% of the total number.
Bacteria have a high reproduction rate, which depends on nutritional conditions, temperature, air access, etc.
Under favorable conditions, the cell can divide every 20-30 min.
That is, 48-72 doubling cycles can occur per day.
What microorganisms form spores
From one cell during this time, 4714169 1015 cells would arise, after 36 hours the microbial mass would be about 400 tons.
If reproduction constantly took place at such a rate, then from one cell within 5 days such a number of cells could be formed that their total volume would be equal to the volume of all seas and oceans.
Virtually continuous division of microbes does not occur.
Many factors interfere with their reproduction: depletion of the nutrient medium, accumulation of products of their own metabolism and other physical, chemical and biological factors of the external environment. So, with a decrease in temperature by 10 ° C, the reproduction rate decreases by 2-3 times.
Getting into new conditions, on a fresh substrate, microbes do not immediately begin to multiply.
Some time passes before the start of an increase in their number (growth retardation phase), during which they adapt to their habitat and prepare the environment itself. After this, rapid reproduction begins, then slowing down as the nutrient resources are exhausted and the products of the vital activity of bacteria accumulate in the environment.
The rapid development of microbiological spoilage of products - souring, oxidation, molding, rotting, etc.
- just due to the exceptionally high rate of reproduction of bacteria.
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Non-spore-forming anaerobes
Clinical significance of the main bacterial pathogens
The modern classification of pathogens of bacterial infections provides for dividing them into two large groups: aerobes and anaerobes(rice.
3.24.2.). In each of these groups, cocci and rods are isolated, which, taking into account the traditional method of microscopic identification of bacteria (Gram stain), are divided into gram positive - gram(+)- and g ram-negative - gram(-). In addition, gram (+) sticks, both aerobic and anaerobic, are divided into spore-forming and non-spore-forming. Separately, intracellular pathogens (chlamydia, mycoplasma, ureaplasma, rickettsia), spirochetes and mycobacteria are considered.
3.24.2. Classification of the main causative agents of bacterial infections
Aerobic bacteria
Gram (+) cocci
Staphylococci .
have the greatest clinical significance Staphylococcus aureus, and from coagulase-negative staphylococci - epidermal (S.epidermidis) and saprophytic (S. saprophyticus).
S. aureus often is the causative agent of infections of the skin and soft tissues, osteomyelitis, arthritis. It can cause nosocomial pneumonia, endocarditis in drug addicts, sepsis.
S.epidermidis causes prosthetic valve endocarditis, catheter-associated infections, and prosthetic joint infections.
S.saprophyticus may be one of the causative agents of cystitis.
streptococci .
The most important are group A beta-hemolytic streptococcus (GABHS, Streptococcus pyogenes), Pneumococcus (S. pneumoniae) and viridescent streptococci (S.mitis and etc.).
GABHS is the main causative agent of bacterial tonsillopharyngitis and scarlet fever.
It also causes infections of the skin (erysipelas, impetigo) and soft tissues (cellulitis, lymphangitis, necrotizing fasciitis, etc.).
S.pneumoniae- one of the most common causative agents of infections of the upper respiratory tract - URT (otitis media, sinusitis) and lower respiratory tract - LRT (exacerbation of chronic bronchitis, community-acquired pneumonia), as well as meningitis.
Viridescent streptococci are one of the main causative agents of endocarditis, brain abscesses and other localizations.
Enterococci .
The main representatives are E. faecalis and E. faecium. They can cause urinary tract infections (UTIs), endocarditis, and less often intra-abdominal and postoperative wound infections.
E.faecium is more resistant to antibiotics.
Gram(+) sticks
Listeria is of the greatest clinical importance. (Listeria monocytogenes), which can cause meningitis in children under 1 month of age and persons over 50 years of age, diphtheria pathogens (Corynebacterium diphtheriae) and anthrax (Bacillus anthracis).
Gram(-) cocci
This group includes members of the genus Neisseria(gonococcus, meningococcus) and Moraxella. Gonococci are the causative agents of gonorrhea. Meningococcus causes meningitis. Moraxella catarrhalis plays a role in respiratory tract infections.
Gram(-) sticks
Members of the family have the greatest clinical significance. Enterobacteriaceae (enterobacteria), "non-fermenting" gram (-) bacteria and Haemophilus influenzae.
FamilyEnterobacteriaceae includes microorganisms such as E. coli (Escherichia coli) salmonella (Salmonella spp.), shigella (Shigella spp.), Klebsiella (Klebsiella pneumoniae and others), protea (Proteus spp.), enterobacter (Enterobacter spp.), serrations (Serratia marcescens etc.), Providence (Providence spp.), citrobacter (Citrobacter spp.), etc.
E.coli is one of the most common causative agents of urinary tract infections (cystitis, pyelonephritis) and prostatitis.
It can also cause intestinal infections, wound infection, intra-abdominal infections. In patients with risk factors (diabetes mellitus, heart failure, etc.), it can cause community-acquired pneumonia.
Salmonella and Shigella cause intestinal infections S. typhi are the causative agents of typhoid fever.
Klebsiella, Proteus, Enterobacter and other members of the family Enterobacteriaceae more often they are the causative agents of nosocomial infections (infections of the urinary tract, intra-abdominal infections, pneumonia, etc.).
Yersinia.Yersinia pestis is the causative agent of the plague Y.
entero-colitica causes yersiniosis, Y. pseudotuberculosis - pseudotuberculosis.
Non-fermenting bacteria . This group includes Pseudomonas aeruginosa (Pseudomonas aemginosa), acinetobacter (Acinetobacter baumanii), Stenotrophomonas maltophilia and etc.
P. aeruginosa - is one of the most important stimuli nosocomial infections, in particular ventilator-associated pneumonia, urinary tract infections, intra-abdominal infections, burn infections, osteomyelitis.
Community-acquired infections are relatively rare: malignant otitis externa, infections in diabetic foot syndrome.
Acinetobacter and other non-fermentative bacteria cause nosocomial infections.
Haemophilus influenzae (Haemophilus influenzae) - one of the main causative agents of infections of the upper respiratory tract (otitis media, sinusitis, epiglottitis) and the RTP (exacerbation of chronic bronchitis, community-acquired pneumonia). In addition, it can cause meningitis, as well as arthritis and osteomyelitis (mainly in children under 5 years of age).
Other gram-negative bacteria.
Campylobacter (Campylobacter spp.) cause intestinal infections.
Helicobacter pylori - causes gastroduodenal erosive and ulcerative lesions.
Pasteurella multocida - one of the causative agents of wound infection after animal bites (cat, dog, pig).
Streptobacillus moniliformis - causative agent of wound infection after a rat bite.
Francisella tularensis- the causative agent of tularemia.
Brucella (Brucella spp.) cause brucellosis.
Haemophilus ducreyi- the causative agent of a soft chancre related to STIs.
anaerobic bacteria
Spore-forming anaerobes
Gram(+) sticks
This group includes clostridia: C.botulinum - the causative agent of botulism; C.tetani- the causative agent of tetanus; C. perfringens - causative agent of gas gangrene; C.difficile- causative agent of antibiotic-associated diarrhea and pseudomembranous colitis.
Non-spore-forming anaerobes
Gram (+) cocci
This group is represented by Peptococcus (Peptococcus niger) and peptostreptococci (Peptostreptococcus spp.), which can cause orodental infections (periodontitis, periostitis of the jaw, etc.), chronic sinusitis, aspiration pneumonia, lung abscess, intra-abdominal infections and infections of the pelvic organs.
Gram(+) sticks
Propionibacterium acnes- is the causative agent of infected acne.
Gram(-) sticks
This group includes bacteroids, prevotella, fusobacteria.
Bacteroids.
4. Spore-forming bacteria, their characteristics, practical significance and distribution.
The most important clinically is Bacteroides fragilis, which more often than all other anaerobes causes intra-abdominal infections (peritonitis, abscesses). It can also be the causative agent of lung abscess, infections of the pelvic organs.
Prevotella(Prevotella bivia, Pmelaninigenicaujxp.), as well as representatives of the genus Porphyromonas- can cause intra-abdominal infections, pelvic infections, orodental infections, chronic sinusitis, aspiration pneumonia, lung abscess.
Fusobacteria.Fusobacterium nucleatim - may be the causative agent of necrotic orodental infections, chronic sinusitis, aspiration pneumonia, lung abscess.
Fusobacterium necrofurum- the causative agent of necrobacillosis.
During the life of microbes, 2 stages are observed:
- vegetative - reproducing and vital.
- resting - viable, but not vital.
Features of the resting stage:
- Features of the physico-chemical structure thicker shell, lower water content.
- Weak permeability to various chemical substances(resistance to
- Higher resistance to damaging environmental factors (antibiotics, etc.)
- Reduced ability to release biologically active substances.
Disputes and spore formation.
Bacterial spores can be considered as a form of preservation of the hereditary information of a bacterial cell under adverse environmental conditions. A relatively small number of both pathogenic and non-pathogenic bacteria have the ability to sporulate. The former include bacteria of the genera Bacillus, Clostridium, the latter - saprophytic representatives of the mentioned genera and some cocci.
The process of sporulation begins with the formation of a sporogenous zone inside a bacterial cell, which is a compacted area of the cytoplasm with a nucleoid located in it.
Then the prospore is formed by isolating the sporogenous zone from the rest of the cytoplasm with the help of the CM growing inside the cell. Between the inner and outer layers of the latter, a cortex is formed, consisting of a special peptidoglycan.
Subsequently, the outer side of the membrane is covered with a dense shell, which includes proteins, lipids and other compounds that are not found in vegetative cells. These include dipicolinic acid, which determines the thermal stability of the spore, etc.
Then the vegetative part of the cell dies off, and the spore remains in the external environment for long periods, measured in many months and years.
The ability of a number of pathogenic bacteria to form spores that persist in the external environment for a long time and have high thermal stability is due to:
- low water content
- high concentration of calcium,
- structure and chemical composition her shells.
The extremely high resistance of spores to physical and chemical factors is of significant epidemiological significance, since it contributes to the preservation of the source of infection and environmental pollution.
Spores of many pathogenic bacteria withstand short-term boiling and are resistant to low concentrations of disinfectants.
Contamination of spores of pathogenic bacteria in damaged areas of the skin can lead to wound infection and tetanus.
Under favorable conditions, the spore germinates into a vegetative cell. The spore swells, which is associated with an increase in the amount of water in it, the activation of enzymes involved in energy and plastic metabolism. Next, the spore shell is destroyed and the growth tube exits from it, after which the synthesis of the cell wall is completed and the formed vegetative cell begins to divide.
Spore germination occurs within 4-5 hours, while spore formation continues until 18-20 hours.
At the same time, the ability of bacteria to form spores that differ in shape, size, and localization in the cell is a taxonomic feature that is used for their differentiation and identification.
Detection of endospores:
- With the usual methods of staining, the spores are not stained and look like unpainted voids inside the stained vegetative cells, since the dense shell of the spores is impermeable to water.
Spores are visible due to their high refractive index - the same as dehydrated proteins. This indicates that bacterial spores contain a large amount of protein-rich material concentrated in a small volume. The spore contains almost all the dry matter of the mother cell, but occupies 10 times less volume.
- Special staining methods are used in cases of doubt. In this case, mordants are used, which loosen the spore shell and facilitate the penetration of the dye. The stained spores are acid-resistant, in contrast to the vegetative body of a microbial cell, which is decontaminated by acid.
bacterial spores
Staining according to Ozheshko: a few drops of 0.5% HCl are applied to a dried non-fixed smear (thick, on the edge of the glass) and heated for 1-2 minutes until boiling, the acid residues are drained; - the cooled preparation is washed with water, dried, fixed on the burner flame; then they are painted as according to Ziehl-Neelsen, 1% malachite green can be used for finishing.
Colored spores (ruby red) are acid-resistant, unlike vegetative microbial cell bodies (blue or green)
- Phase contrast microscopy.
- Electron microscopy.
Exospores, unlike endospores, are formed outside the bacterial cell and are the mode of reproduction in actinomycetes.
There is not one, but many spores per bacterial cell. Exospores are less stable in the external environment.
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There are some types of bacteria that produce round or oval-shaped bodies that are highly refractive. These formations are called endospores. Spore formation is one of the stages of the development cycle of certain microorganisms in response to the adverse effects of the external environment, developed in the process of evolution in the struggle for the preservation of the species. Nutrient deficiency causes various reactions in some microorganisms that prepare the cell for a long period during which nutrients are not available. The transition to sporulation is observed when the nutrient substrate is depleted, with a lack of carbon, nitrogen or phosphorus, a change in the pH of the medium, etc. Sporulation is inherent mainly in rod-shaped microorganisms (bacilli and clostridia, and relatively rarely observed in cocci (Sarcina urea, Sarcina lutea) and convoluted forms (Desulfovibrio desulfuricans).
Sporulation occurs in the external environment, on nutrient media and is not observed in human and animal tissues. The process of sporulation is divided into seven successive stages, characterized by various cytological changes (Fig. 12).
Preparatory stages(stages 0 and I). At these stages, there are no morphologically visible changes in the cell yet, but the amount of water decreases and the cytoplasm becomes denser.
Prospore stage(stage II) is the first stage of sporulation recognizable morphologically. It is characterized by the appearance of a prospore septum, which divides the cell into a small prospore and a large mother cell. This is the key stage of sporulation.
During prospore absorption stages(stage III) there is a spatial separation of a small prospore, which passes into the cytoplasm of the mother cell. Outside the prospore, a double membrane structure is formed.
Prespore stage characterized by the formation of a cortex (a dense spore membrane) inside the membrane structure of the prospore (stage IV) and the condensation of proteins on its surface (stage V).
On the ripening stages(stage VI) the spore coat develops further and becomes resistant to chemical agents and heat. The formed spore occupies approximately 1/10 of the mother cell.
The final stage is mature spore release from the mother cell (stage VII). The process of spore formation proceeds within 18-20 hours.
Due to the presence of a dense multilayer shell having a lamellar structure, a minimum amount of water and a high content of calcium, lipids and dipicolinic acid, spores are highly resistant to environmental factors and disinfectants. They withstand relatively high and low temperatures, prolonged drying, exposure to radiation, toxic substances, etc. They can survive for decades under adverse conditions.
Once in favorable conditions, spores germinate and again turn into vegetative forms. The process of spore germination begins with the absorption of water. They swell, increase in size. From the shell on the pole, in the center or between the pole and the center, a process appears, from which the stick is pulled out. The process of spore germination is much faster and takes 4-5 hours.
By the nature of localization in the body of microorganisms, spores are located:
1. Central (anthrax stick, anthracoid stick, etc.).
2. Subterminally - closer to the end (the causative agent of botulism, etc.).
3. Terminal - at the end of the stick (the causative agent of tetanus).
In some species of spore-forming microorganisms, the diameter of the spores exceeds the diameter of the bacterial cell. If the spores are localized subterminally, such bacteria take the form of a spindle. These include clostridia of butyric fermentation. In some clostridia, for example, in the causative agent of tetanus, spores are located terminally, their cell resembles a drumstick (Fig. 13).
Rice. 13. Shapes and location of spores in bacilli.
The ability to spore formation is used in the systematics of microbes, as well as in the choice of methods for disinfecting objects, premises, food products, and various products.