1.4.3.3. Causative agents of mycobacteriosis.
Many types of mycobacteria can cause opportunistic diseases in humans or mycobacteriosis. The problem of mycobacteriosis has significantly worsened due to the global spread of HIV infection. When cellular immunity is suppressed, mycobacteria become one of the leading opportunistic pathogens.
The pathogens are widespread in the environment and are found in water and soil. They are excreted from the body of humans, warm-blooded and cold-blooded animals.
Most often, diseases are caused by a closely related group of mycobacteria, which are classified as M.avium (M.avium complex or MAC).
Independent types of mycobacteriosis are associated with infection M. kansasii, M.ulcerans, M. scrofulaceum, M.chelonae, M.fortuitum.
Complex M.avium includes several subspecies. Among them is the subspecies of the same name M.avium subsp.. avium, as well as subspecies M.hominissius, M.silvaticum, M.paratuberculosis. They are adjacent to a genetically similar species M.intracellulare.
M.avium is the causative agent of tuberculosis in birds, but it can also infect humans. The infection is usually transmitted by airborne droplets, less often by nutrition.
In patients with HIV infection in the AIDS stage, the bacterium causes generalized damage involving the respiratory and gastrointestinal tract. Severe mycobacteriosis is observed in 25-30% of patients with HIV infection during a long course of the disease.
Also M.avium may cause cervical lymphadenitis in children and pulmonary pathology in adults.
Pathogenic for humans M.avium proposed to be classified as a subspecies M.hominissius.
Subspecies M.paratuberculosis causes hypertrophic enteritis in cattle. It is suspected of being involved in the development of Crohn's disease in humans.
Subspecies M.sylvaticum is the cause of tuberculosis in wood pigeons.
View M.intracellulare was first isolated from a sick person. Subsequently, it was discovered in animals, as well as on objects environment where bacteria form biofilms. In humans, it can cause severe lung disease, and can affect individuals without immunodeficiency.
Other mycobacteria can also cause pulmonary lesions. Among them they find M. kansasii, M.simiae, M. scrofulaceum. In addition to pulmonary infections, M. scrofulaceum often causes cervical lymphadenitis in children.
M.ulcerans is the causative agent of Buruli ulcer - lesions of the skin, subcutaneous tissue with transition to bone tissue, which is accompanied by necrosis and ulceration. The disease is found in residents of tropical Africa, Australia, and Latin America. The pathogen secretes a lipid toxin - mycolactone which contributes to the development of the disease.
Fast-growing species that are pathogenic for humans include: M.fortuitum And M.chelonae. They can cause wound infections, post-injection abscesses, corneal ulcers, and pulmonary lesions.
Laboratory diagnosis of mycobacteriosis includes microscopy clinical material with Ziehl-Neelsen staining of bacteria followed by their isolation in pure culture.
The most modern are genetic methods for identifying pathogens of mycobacteriosis.
For the treatment of infections caused by the complex M.avium, macrolide antibiotics and rifabutin are prescribed, since the pathogens are resistant to first-line anti-tuberculosis drugs.
For local mycobacterial processes (lymphadenitis, ulcers), along with antibiotic therapy, surgical treatment is used.
14.4. Pathogenic actinomycetes
The first description of actinomycosis in humans was made by W. Langenbeck in 1845; the pathogen was isolated in pure culture in 1887 by K. Hartz and in 1888 by M. Afanasyev.
Classification
These bacteria belong to the order Actinomycetales, family Actinomycetaceae, family Actinomyces. The genus includes more than 30 species, among them A. israelii,A.gerencseriae, A. naeslundii, A.viscosus,A. bovis and many more etc.
In terms of morphological organization, actinomycetes are similar to fungi (name " actinomyces" comes from two words: actis beam and myces- mushroom), but their genetic apparatus is represented by a nucleoid.
Morphology
Actinomycetes can be represented by straight or curved rods, often forming filaments. They have branched nonseptate substrate or aerial mycelium with spores. They are immobile and reproduce by spores, budding, and fragmentation. Some actinomycetes can form a polysaccharide capsule around the mycelial filaments.
Gram-positive, there are acid-fast and acid-sensitive variants. In the affected tissues they form Druze(intertwined mycelium).
Cultural properties
Among actinomycetes there are facultative and strict anaerobes, the latter being more often pathogenic. Actinomycetes require CO 2 for their growth. The optimal growth temperature is 35-37 0 C. Growth is slow, from 7 to 14 days. They can dissociate into R- and S-forms and produce smooth and spider-like colonies.
They grow well on blood agar, serum agar, and Sabouraud's medium. On blood agar, many species produce hemolysis; on other solid media, young colonies are flat and easily removed from the agar; mature cultures can be lumpy, crumbly, and are more tightly bound to the medium.
Actinomycetes often have pigments of different colors (red, purple, green).
Biochemical properties
Biochemical properties are variable and differ between species. Actinomycetes have saccharolytic and proteolytic activity. The most virulent pathogens are strict anaerobes.
Antigenic structure
They have a specific cell wall antigen. According to their antigenic structure, actinomycetes are divided into 5 serogroups (A, B, D, E, F).
Distribution and ecology
Actinomycetes are part of the normal anaerobic microflora oral cavity, gastrointestinal tract, vagina, there are many of them in the stroma of dental calculus, tonsil crypts, salivary glands, in concretions (stones) of the biliary and urinary tracts. They are naturally released into the environment, where they can multiply at temperatures from 3-7 0 C to 40 0 C and persist long time. In nature, they are found in all geographical latitudes.
These bacteria play an important role in soil ecology, causing the degradation of plant residues, lignin, and chitin. Among actinomycetes there are strains that produce antibiotics, bacteriocins, and vitamins.
Resistance
Actinomycetes are resistant microorganisms; they are insensitive to drying, freezing and thawing. Antiseptics act on them in high concentrations, as well as on spore cultures.
Characteristics of diseases
Actinomycetes, as representatives of normal microflora, are generally characterized by low virulence.
However, many of them can stimulate inflammatory processes of various localizations, primarily in the oral cavity and maxillofacial area. In most cases, these are nonspecific mixed infections caused by different types of pathogens.
Involved in the development of periodontal diseases A. israelii,A.gerencseriae, A. naeslundii, A.viscosus, A. odontolyticus.
In some cases, actinomycetes can cause urogenital infections, especially in women using intrauterine contraceptives. Possible organ infections abdominal cavity after surgery or injury.
Specific infection or actinomycosis is a chronic granulomatous purulent lesion of various systems and organs, which is characterized by tissue infiltration followed by suppuration and possible formation of fistulas.
The main causative agents of human actinomycosis are A. israelii, less often A. naeslundii, A. viscosus, A. meyeri.
The disease can develop as a result of exogenous and endogenous infection, often as a result of autoinfection against the background of immunodeficiency, trauma, and purulent-inflammatory lesions.
Source of infection– infected people or animals.
Transmission routes– airborne, contact, less often alimentary.
Entrance gate– skin and mucous membranes. The development of infection is associated with a violation of the integrity of the integumentary tissues.
The pathogen spreads hematogenously and lymphogenously. In tissues, actinomycetes form Druze, leukocytes accumulate around them, granulation tissue is formed, in which there are many plasma cells, epithelioid cells and fibroblasts. In the center of the drusen, cell necrosis and tissue breakdown occur. Secondary infections due to pyogenic cocci may occur. When actinomycetes metastasize to the brain or mediastinum, the disease often ends in death (Fig. 16).
Depending on the location, there are several clinical forms of the disease: cervicofacial, thoracic, abdominal, etc.
The course of the disease is aggravated by immunodeficiencies, autoimmune reactions and hyperthyroidism.
Immunity
Immunity does not develop with actinomycosis. Antibodies do not perform a protective function.
Laboratory diagnostics
Material for research: pus from fistulas, sputum, cadaveric material, etc.
Bacterioscopic method. A “crushed drop” preparation is prepared, emulsifying the material to 10-20%. You can prepare smears and stain them according to Romanovsky-Giemsa. Drusen or threads of thin nonseptate non-branching mycelium are found.
Bacteriological method. The material is inoculated on blood agar, serum agar, Sabouraud medium or brain heart broth. Crops are incubated for 1-2 weeks under aerobic and anaerobic conditions. Identification is carried out taking into account cultural, biochemical and antigenic properties.
Allergic method. HCT is determined in a skin test with actinolysate.
Serological method. In paired sera, an increase in antibody titer is detected in ELISA, RSK, RPGA.
Treatment
Pathogens remain sensitive to penicillin; doxycycline or sulfonamides can be used. The duration of taking medications is at least 4-6 weeks. Also used surgical methods– excision of affected tissue.
Prevention The disease is only nonspecific.
14.5. Listeria
In 1924, E. Murray isolated from the blood of laboratory animals the new kind gram-positive rods, which were called Bacteriummonocytogenes. In 1929, A. Nifeldt isolated a similar pathogen from a person with tonsillitis and high monocytosis. In 1940, at the suggestion of J. Peary, the genus of the pathogen was named Listeria, and the disease was called “listeriosis.”
Classification
Pathogens belong to the family Listeriaceae, family Listeria. The genus includes 6 species, among them L. monocytogenes, L. ivanovii, L. murrayi etc. The type species is L. monocytogenes, representatives of which are isolated from humans and animals and can cause diseases in them.
Morphology
Listeria are small gram-positive rods or coccobacteria. They do not have spores, capsules, and are peritrichous (form 1-5 flagella). Mobility is maximum at 20-28 o C. In smears they can be arranged randomly, at an angle to each other, in chains or parallel rows.
Cultural properties
Pathogens are cultivated at 35-37 o C on blood agar, chocolate agar, trypticase soy broth and agar, thioglycollate medium. Can grow at more low temperatures. Incubation lasts 5-7 days with daily growth monitoring.
On blood agar they form small (up to 1 mm) translucent colonies, which give narrow zones of β-hemolysis. When growing on most media, colonies resemble dew drops.
To improve isolation conditions, selective media with antiseptics and antibiotics (acriflavine, polymyxin, nalidixic acid) are used.
Bacteria can dissociate into S- and R-forms. S-forms are small, round, slightly convex, translucent colonies; R-forms are rough, coarse-grained colonies with jagged edges.
On liquid media, Listeria produces a uniform turbidity followed by the formation of a sediment.
Biochemical properties
They belong to facultative anaerobes. The pathogens are catalase positive.
Saccharolytic activity is pronounced. They decompose glucose and maltose to acid, and slowly ferment sucrose, glycerin and lactose. Mannitol and starch do not decompose.
They do not form indole and hydrogen sulfide, and do not reduce nitrates to nitrites.
Antigenic structure
Listeria has a somatic, heat-stable O-antigen and a flagellar, heat-labile H-antigen. There are 13 different serovars known.
Pathogenicity factors
Microbial adhesins And teichoic acids are responsible for the adsorption of the pathogen on cells. The leading adhesin is a protein internalin.
The main toxin of Listeria is hemolysin or O-listeriolysin. It damages cell membranes ( pore-forming toxin) and ensures the release of Listeria from phagosomes during phagocytosis. Enzymes have a similar effect phospholipases.
Surface proteinActA causes actin polymerization in affected cells, which determines the intracellular mobility of Listeria and their intercellular spread.
O-listeriolysin, phospholipases and ActA protein are encoded by genes chromosomal pathogenicity island listeria.
Microbial siderophores provide pathogens with iron ions.
Glycolipid analogue endotoxin stimulates inflammation.
Resistance
Pathogens have significant resistance. They persist for a long time in soil and wastewater and are able to multiply in feces and organic plant debris. Compared to other non-sporeless bacteria, Listeria is resistant to heating, drying, and freezing.
Pathogenesis and characteristics of the disease
Listeriosis- This zoonotic a disease that is accompanied by damage to the immune and nervous system with the involvement of internal organs and subsequent septicemia.
Listeriosis is a disease with natural focality. The reservoir of the pathogen in nature is many species of rodents.
Sources of infection there may be many domestic and wild animals, birds (more than 50 species in total).
Transmission routes diseases - a person becomes infected most often through the alimentary route through water and food products contaminated with the pathogen, less often through airborne droplets and contact routes during cutting meat, processing hides, and even transmissible through ticks and other blood-sucking arthropods.
A vertical route of infection from a sick mother is possible; the risk of infection of the fetus during pregnancy increases by more than 10 times.
Infectious dose in sensitive individuals it is small (less than 1000 microorganisms).
Incubation period can last from several days to 2-3 weeks.
Bacteria enter the human body through the airways, gastrointestinal tract, mucous membranes of the pharynx, eyes, and through damaged skin.
Listeriosis is an intracellular infection. Microbial adhesins ensure tight attachment of the pathogen to the epithelium. Membrane receptors for internalina listeria are cellular molecules- cadherins. Binding of internalin leads to the capture and phagocytosis of Listeria by epithelial cells, macrophages and monocytes, and neutrophils.
After Listeria enters the cells, they destroy the phagosome membrane using O-listeriolysine and enter the cytoplasm of phagocytes. This prevents bacteria from being digested.
At 37 o C, bacteria in the cells of the human body lose their mobility. However, listeria proteinActA polymerizes intracellular actin, causing the formation of actin filaments. The filaments attach to the pole of the microbial cell. Formed "actin comet"(or “propeller”), which ensures the intracellular motility of Listeria.
Affected epithelial cells form membranous outgrowths or filopods, through which Listeria infects neighboring cells.
As a result of infection of macrophages, monocytes, neutrophils, bacteria spread in the body, penetrate the blood and lymph. They can affect the tonsils, liver, spleen, lungs, adrenal glands, and central nervous system.
The clinical manifestations of the disease are very diverse. Fever develops. The local form of listeriosis occurs as gastroenteritis.
More common angino-septic form, less often nervous, oculoglandular. Marked pneumonia, meningitis.
Listeriosis in pregnant women often leads to fetal death, spontaneous abortion and miscarriage. Newborns experience septic-granulomatous form of the disease or listeria meningitis.
The prognosis of the disease is usually favorable, however, with a detailed clinical picture of the disease, mortality remains very high - 25-30%. With listeria septicemia, the mortality rate exceeds 50%, with menigitis - more than 70%.
Immunity
Immunity is cellular in nature and, to a lesser extent, humoral. It is believed that the majority of the adult population has sensitized lymphocytes to the pathogen.
After the disease, a long-lived clone of memory cells is formed, which provides lasting immunity.
Laboratory diagnostics
Material depends on the stage and form of the disease. They examine mucus from the throat, punctate of enlarged lymph nodes, blood, cerebrospinal fluid, and in newborns, umbilical cord blood. In case of fetal death, sectional material is examined.
A preliminary diagnosis of some forms of listeriosis can be established by bacterioscopy amniotic fluid or cerebrospinal fluid with Gram stain.
Bacteriological method. The test material is inoculated on glucose-liver or glucose-glycerol broth. Cultivate at 37 0 C for up to three weeks. Day-old colonies with zones of hemolysis are examined under a microscope. Then they are subcultured onto glucose-blood agar or other solid media.
The isolated culture is identified by morphological, cultural, tinctorial, biochemical and antigenic properties in the agglutination reaction. It is possible to use systems for automated biochemical identification of pathogens.
Key Characteristics Used for Differentiation L.monocytogenes from other types of listeria
|
L.monocytogenes |
L.ivanovii |
L.seeligeri |
L.innocua |
L.welshimeri |
L.grayi |
|
|
Mannitol fermentation Xylose fermentation Fermentation of rhamnose | ||||||
|
Beta hemolysis | ||||||
|
CAMP test Increased hemolysis near the stroke: Rhodococcus equi Staphylococcus aureus | ||||||
|
Hydrolysis of lecithin without carbon Hydrolysis of lecithin with coal | ||||||
|
Pathogenicity to humans |
Missing |
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Serological method used from the second week of the disease in dynamics. They perform RSC, agglutination test, ELISA or indirect RIF.
Express diagnostics. To identify the antigen in the test material, RIF is used. Polymerase chain reaction (PCR) can be used to determine the nucleic acids of the pathogen.
Less commonly used biological sample on white mice. After the death of the mice, protocol cultures are taken from the internal organs of the corpse, and the culture is isolated and identified.
Treatment
The pathogen is resistant to cephalosporins, moderately resistant to fluoroquinolones. Treatment is carried out with benzylpenicillin or amoxicillin, a combination with macrolides is possible. For allergies to β-lactams, co-trimoxazole and doxycycline are used.
Prevention only nonspecific. It comes down to a set of sanitary and veterinary measures carried out on livestock farms and slaughterhouses. In the outbreaks, deratization and destruction of stray cats and dogs are carried out. In areas unfavorable for listeriosis, dairy products are subject to mandatory heat treatment.
Genus Mycobacterium.
Mycobacteria are acid-fast, non-motile, gram-positive, rod-shaped (straight or curved) bacteria capable of forming filamentous and mycelial structures. They are characterized by a high content of lipids and waxes in the cell walls, which ensures resistance to alcohols, acids, alkalis, disinfectants, drying and exposure to sunlight, poor stainability with dyes, high hydrophobicity, and pathogenicity.
Along with acid resistance, an important characteristic of mycobacteria is slow growth on nutrient media, especially mycobacterium tuberculosis. Another feature of mycobacteria is the formation of pigments; some species form pigment in the dark.
Among pathogenic mycobacteria, the main causative agent of human tuberculosis is M.tuberculosis (Koch's bacillus), M.bovis is the causative agent of tuberculosis in cattle and M.leprae is the causative agent of leprosy. Diseases in humans can also be caused by M.avium, the causative agent of avian tuberculosis, and about 20 other potentially pathogenic species that can cause atypical forms of lesions in humans (mycobacteriosis).
Mycobacterium tuberculosis (Koch bacillus).
Morphological properties typical for mycobacteria. These are thin straight or slightly curved rods with granular formations in the cytoplasm; coccoid structures and L-forms may occur. Acid-stable (high content of lipids and mycolic acid in the cell wall). They have acid-labile granules (Much granules) in the cytoplasm. Gram-positive, poorly dyed with aniline dyes, Ziehl - Nielsen they are painted bright red.
Cultural properties. They grow in aerobic and optionally anaerobic conditions. They grow very slowly - within a few weeks. Mycobacteria need protein and glycerol, growth factors. The most commonly used dense egg media are Levenstein-Jensen, Finn II, synthetic and semi-synthetic liquid media.
On solid media, growth is noted on days 15-40 in the form of a dry, wrinkled, cream-colored coating (R-form), colonies in appearance resemble cauliflower. In liquid media, growth is observed in the form of a surface film.
Koch's bacillus is stable in the external environment and persists in dried biosubstrates for up to several weeks.
Pathogenicity factors. The pathogenic properties of the tuberculosis bacillus and the biological reactions with which the macroorganism responds to the introduction of the pathogen are associated with the characteristics of its chemical composition, the high content of lipids and their composition (the presence of fatty acids - phthioid, mycolic, tuberculostearic etc., phosphatides and other fractions).
The main factor is a toxic glycolipid - “cord - factor”, easily detected when cultivated in liquid media. It ensures close proximity of mycobacteria in the form of braids, tourniquets, and cords. The cord factor has toxic effect on tissue, and also blocks oxidative phosphorylation in the mitochondria of macrophages (protects against phagocytosis). WITH chemical composition mycobacteria are associated with two more important characteristics:
- ability to cause pronounced HRT reaction, detected using a tuberculin test - “tuberculin-type HRT.”
Antigenic structure. Mycobacterium tuberculosis has a complex and mosaic set of antigens. Antigenically, M. tuberculosis is most similar to M. bovis and M. microti. There are cross-reacting antigens with corynebacteria and actimomycetes. Antigenic properties are practically not used to identify mycobacteria.
Epidemiology. The main routes of infection are airborne droplets and airborne dust. The main source of infection is a person with tuberculosis. Overcrowding of residence plays a special role; in Russia, places of detention, refugee camps, people without a fixed place of residence and other socially disadvantaged groups of the population are of greatest importance. In a relatively small percentage of cases, tuberculosis is caused by infection from animals (usually through milk) by M. bovis.
Pathogenetic features.
During life, a person repeatedly comes into contact with Mycobacterium tuberculosis, but tuberculosis pathological process Not all infected people develop. This depends on many factors and, above all, the body’s resistance.
Most often, infection occurs through the respiratory tract. Mycobacteria that enter the body are captured by alveolar and pulmonary macrophages. May develop at the site of contact primary affect (bronchopneumonic focus). Next, the pathogen is transported to regional lymph nodes, causing an inflammatory reaction - lymphangitis and lymphadenitis. Primary affect, lymphangitis and lymphadenitis - primary complex (primary focus of tuberculosis), characterized by the formation of granulomas in the form of tubercles along the lymphatic tract and nodes ( tuberculosis or tuberculosis).
The formation of granulomas is a cellular response of DTH to a number of chemical components of mycobacteria. In the center of the granuloma, in the focus of necrosis (caseous decay), there are mycobacteria. The lesion is surrounded by giant multinucleated Pirogov-Langhans cells, they are surrounded by epithelioid cells and on the periphery - lymphocytes, plasma and mononuclear cells.
Outcomes of the primary lesion:
- with sufficient resistance organism, the reproduction of the pathogen in granulomas stops, the focus is surrounded by a connective tissue capsule and becomes calcified (calcium salts are deposited). This process is determined by the formation non-sterile infectious immunity to the causative agent of tuberculosis. Nonsterility - the ability of mycobacteria to persist for a long time in the primary focus and wait in the wings (sometimes after several decades);
- with insufficient resistance- increased caseous decay of the focus, caseous pneumonia, severe primary pulmonary consumption and generalized tuberculosis (disseminated or miliary tuberculosis with granulomas in various organs).
Secondary tuberculosis. The secondary tuberculosis process - reactivation of the pathogen as a result of weakening resistance is observed under stress, nutritional disorders and in the elderly. Foci of caseous decay appear in the lungs with the formation of cavities, damage to the bronchi and small blood vessels.
Immunity. The basis of non-sterile infectious and vaccine immunity in tuberculosis is cellular immunity in the form of delayed-type hypersensitivity (DTH), mediated by T lymphocytes and macrophages. T lymphocytes, with the participation of proteins of the major histocompatibility system class I, recognize cells infected with Mycobacterium tuberculosis, attack and destroy them. Antibacterial antibodies bind to various antigens pathogen, form circulating immune complexes (CIC) and promote their removal from the body.
Allergic transformation (HRT) to the tuberculosis bacillus indicates the formation of acquired immunity and can be detected using a tuberculin test. This test is quite specific. Old Koch tuberculin is a concentrated filtrate of sterilized mycobacterial components. The purified preparation PPD (Koch's new tuberculin containing tuberculoproteins) is used primarily for staging intradermal Mantoux test. Using this sample, individuals subject to revaccination are selected. A positive Mantoux test result cannot be considered as an obligatory sign active process(this is actually an indicator of HRT), and a negative one does not always indicate its absence (anergy, immunodeficiency).
Immunoprophylaxis involves intradermal injection of an attenuated strain of B. bovis known as bacillus Calmette-Gérin (BCG). In Russia, vaccination is carried out for newborns (5-7 days of life), revaccination - at 7-12-17-22 years of age and older with a negative Mantoux test (i.e., the absence of cellular non-sterile = vaccine or infectious immunity - HRT).
Laboratory diagnostics. They use microscopic, bacteriological, biological, allergological, serological and molecular - genetic methods.
Microscopic diagnostics includes microscopy of native material, the use of accumulation methods, and luminescent diagnostics. Microscopy of native pathological material(sputum, fistula discharge, bronchial lavage water, urine) in Ziehl-Neelsen stained smears allows identifying red acid-fast bacilli with a concentration of mycobacteria of at least several hundred thousand/ml. Saving methods(eg flotation) increase the sensitivity of microscopy to several thousand microbial bodies/ml. Fluorescence microscopy using acridine orange or auramine - rhodamine - the most sensitive and effective method bacterioscopy, sensitivity - 500-1000 mycobacteria / ml. Allows you to identify mycobacteria with altered cultural and tinctorial properties.
Bacteriological method(inoculation on nutrient media) makes it possible to detect mycobacteria at a concentration of 200-300/ml. It is most effective before or at the beginning of treatment; at the end of treatment it is inferior in effectiveness to the luminescent method. The disadvantage is the duration of obtaining results - from 2 to 12 weeks. The advantage is the ability to assess the virulence of a culture, determine sensitivity to medicines. Accelerated isolation methods have been developed. According to Price's method, the material is placed on a glass slide, treated with sulfuric acid, washed with saline and added to a nutrient medium with citrated blood. The glass is removed after 3-4 days and stained according to Ziehl-Nielsen.
Gold standard - biological sample on guinea pigs, allows the determination of up to 10 mycobacteria per ml. The spread of resistant and modified mycobacteria has reduced the sensitivity of the method. The method requires compliance with strict conditions and is used in large specialized laboratories.
Allergological methods- these are widely used skin tests with tuberculin and in vitro allergy diagnostic methods (RTML, PPN - an indicator of neutrophil damage, etc.).
Serological methods are numerous (RSK, RA, RPGA), but due to lack of specificity they are used little.
The most perfect genetic methods, they are not yet used enough in practical laboratories.
Among methods for identifying mycobacteria Two approaches have the greatest practical value:
Methods for differentiating M.tuberculosis and M.bovis from other mycobacteria;
Methods for differentiating M. tuberculosis and M. bovis.
There are a number of methods for differentiating the two main types of mycobacteria from the rest. Of these, the simplest and most accessible is to assess growth on an egg medium containing salicylic sodium at concentrations of 0.5 and 1.0 mg/ml. On these media, unlike other mycobacteria, M. tuberculosis and M. bovis do not grow.
To differentiate M. tuberculosis from all other types of mycobacteria, including M. bovis, use niacin test(determination of nicotinic acid synthesized by M. tuberculosis in large quantities, detected using cyanide or thiocyanate compounds by a bright yellow color). Mycobacterium tuberculosis also shows a positive nitrate reduction test. The growth rate and the nature of pigment formation are taken into account. Cytochemical methods are used to identify the cord factor (virulence) by the strength of the bond of dyes - neutral red or Nile blue when treated with alkali.
This type of mycobacteria has been identified in 60 species of mammals. Cattle and, less commonly, camels, goats, sheep, pigs, dogs, and cats pose an epidemic danger to humans. Sick animals excrete mycobacteria in milk, sputum, and excrement. A person becomes infected by caring for sick animals or consuming raw milk and dairy products (the pathogen can survive in cheese and butter for more than 200 days). This pathogen accounts for up to 5% of tuberculosis cases (a high proportion of bovine-type tuberculosis is in Yakutia and other territories with a high incidence of tuberculosis in animals).
Mycobacterium leprosy is the causative agent of leprosy (leprosy) - a generalized chronic infection with predominant damage to the ectoderm derivatives (integumentary tissues and the peripheral nervous system).
Cultural properties. They are very poorly cultivated on nutrient media. The main diagnostic method is bacterioscopic. Differentiation from Mycobacterium tuberculosis can be carried out in a bioassay on white mice (M.leprae is not pathogenic for them).
Epidemiology. The disease is slightly contagious. Genetic predisposition and individual resistance to infection are important. Infection occurs through contact - household and airborne - by drip. They keep patients in leper colonies (the main way of prevention is isolation).
Clinical and pathogenetic features. The incubation period is very long (from 4-6 years). There are tuberculoid (more benign) and lepromatous (more severe) forms.
Treatment long-term, sometimes lifelong. The main drugs are sulfones, the drugs of choice are dapsone, rifampicin, clofazimine.
Lecture No. 6. Family Enterobacteriaceae. Genus Salmonella.
general characteristics family of enterobacteria.
Bacteria of this family are the most common pathogens intestinal infections. They are united by a number common features. These are short, non-spore forming rods with rounded ends, motile (peritrichs) or immobile, some have capsules. Aerobes or facultative anaerobes. A negative Gram stain is characteristic. They grow well on regular nutrient media with meat extract. On most solid media, enterobacteria form round, convex, shiny S- (smooth) colonies, as well as flat, uneven and granular R- (rough) forms, often due to the loss of the capsule. They are characterized by the fermentation of glucose (and other carbohydrates) with the formation of acid and gas. In relation to lactose, they are divided into lactose-fermenting and lactose-non-fermenting. Catalase is positive, reducing nitrates to nitrites.
The Enterobacteriaceae family includes more than 20 genera, uniting more than 100 species of bacteria that live in the soil, on plants, and are part of the microbial biocenoses of the intestines of animals and humans. The genera Escherichia, Salmonella, Shigella, Yersinia, Proteus, Klebsiella, etc. are of greatest importance for humans. To differentiate genera, biochemical characteristics are used mainly; for classification within genera and species, the study of the antigenic structure (O-, H- and K-antigens) is used. .
O-antigen represented by lipopolysaccharides (LPS) of the outer membrane. Strains lacking the O antigen form R colonies and are usually avirulent.
H-antigen - thermolabile proteins are found only in motile (flagella-bearing) species.
K-antigen- thermostable polysaccharides of the capsule and outer shell.
In the pathogenesis of lesions caused by enterobacteria, LPS (endotoxin released when bacteria are destroyed), various enterotoxins, invasiveness and adhesion factors (flagella, etc.), and pathogenicity enzymes are important.
Genus Salmonella.
Salmonella is a large group of enterobacteria, among which various serotypes are pathogens typhoid fever, paratyphoid fevers A, B and C and the most common foodborne toxic infections - salmonellosis. Based on their pathogenicity for humans, Salmonella are divided into pathogenic for humans - anthroponoses (cause typhoid fever and paratyphoid A and B) and pathogenic for humans and animals - zoonoses (cause salmonellosis). Despite the significant differences between Salmonella in antigenic characteristics, biochemical properties, and the diseases they cause, according to the modern, but insufficiently convenient and perfect classification, two species are distinguished - S.bongori and S.enteritica. The latter is divided into subspecies, of which the subspecies choleraesuis and salamae are the most important. The subspecies choleraesuis contains the largest proportion of known Salmonella serovars (about 1400 of about 2400).
Morphology. Straight gram-negative rods measuring 2-4 x 0.5 µm. Motile due to the presence of peritrichial flagella.
Cultural and biochemical properties. Facultative anaerobes, grow well on simple nutrient media. Optimum pH - 7.2-7.4, temperature - +37. Metabolism - oxidative and fermentative. Salmonella ferment glucose and other carbohydrates to produce acid and gas (the Salmonella typhi serotype does not cause gas formation). Usually lactose (on media with this carbohydrate - colorless colonies) and sucrose are not fermented. Oxidase is negative, catalase is positive. The Voges-Proskauer reaction is negative.
Based on their biochemical (enzymatic) properties, Salmonella are divided into four groups. Characteristic signs of salmonella - hydrogen sulfide formation, lack of indole production and aerobic activity. For isolation, differential diagnostic media (bismuth - sulfite agar, Endo, Ploskirev, SS agar) and enrichment media (selenite broth, bile broth, Rappoport medium) are used. S-forms form small (from 1 to 4 mm) transparent colonies (on Endo medium - pinkish, on Ploskirev medium - colorless, on bismuth - sulfite agar - black, with a metallic sheen). In liquid media, S-forms give uniform turbidity, R-forms give a sediment.
Antigenic structure. O-, H- and K-antigens are isolated. The group of K-antigens includes Vi-antigens (virulence antigens). Due to its more superficial location (than O-antigens), Vi-antigen can prevent agglutination of Salmonella cultures with O-specific serum (shielding). To differentiate Salmonella, a scheme (serological classification) is used Kaufmann-White.
According to the structure of O-antigens, Salmonella are divided into O-groups(67 serogroups), each of which includes serological types, differing in the structure of H-antigens. The belonging of Salmonella to a specific serovar is established by studying the antigenic structure in accordance with the Kaufmann-White scheme. Examples: serotype S.paratyphi A belongs to serogroup A, S.paratyphi B belongs to serogroup B, S.paratyphi C belongs to group C, S.typhi belongs to serogroup D.
Pathogenicity factors.
1.Adhesion and colonization factors.
3.Endotoxin (LPS).
4. Heat-labile and heat-stable enterotoxins.
5. Cytotoxins.
6. Virulence plasmids and R-plasmids are essential.
7. Vi - antigen inhibits the action of serum and phagocytic bactericidal factors.
The main pathogenicity factors of Salmonella are their ability to penetrate macrophages and multiply in the lymphoid formations of the mucous layer itself small intestine(Peyer's patches, solitary follicles), as well as endotoxin production.
Pathogenesis of lesions. Differences clinical forms diseases caused by Salmonella depends on the virulence and dose of the pathogen and the condition immune system body. The usual dose that causes clinical manifestations is 10 6 - 10 9 bacteria; a smaller dose is sufficient for immunodeficiencies, hypochlorhydria and other diseases of the gastrointestinal tract.
The following main forms of salmonella infection are distinguished:
Gastrointestinal;
Generalized (typhoid-like and septicopyemic variants);
Bacterial carriage (acute, chronic, transient).
Significant pathogenetic features of the infectious process caused by serotypes S.typhi, S.paratyphi A,B are the basis for classifying typhoid paratyphoid diseases into an independent nosological group. Each phase of pathogenesis corresponds to a clinical period of the disease and its own laboratory examination tactics. Main phases - introduction of the pathogen (corresponds to incubation period), primary localization of the pathogen (prodromal period), bacteremia (first week of the disease), secondary localization of salmonella (the height of the disease - 2-3 weeks), excretory-allergic (reconvalescence - 4 weeks of the disease).
Salmonella entering through the mouth enters the epithelial cells of the duodenum and small intestine through endocytosis. They easily penetrate epithelial cells, but do not multiply here, but pass and multiply in the lymphatic apparatus of the small intestine. Salmonella multiply predominantly in the lamina propria (primary localization), which is accompanied by a local inflammatory reaction of the mucous membrane, an influx of fluid into the lesion and the development of diarrhea syndrome (gastroenteritis). Enterotoxins increase the level of cyclic adenomonophosphate (cAMP), an increase in the level of histamine and other biologically active substances, and vascular permeability. Water and electrolyte disturbances are observed, hypoxia and acidosis develop, which aggravate the pathological process with a predominance of vascular disorders. Some Salmonella are destroyed with the release of endotoxin and sensitization (HRT) of the lymphatic apparatus of the small intestine occurs.
From the mucous membrane, salmonella can enter the lymph and then into the bloodstream, causing bacteremia. In most cases, it is transient in nature, because Salmonella are eliminated by phagocytes.
Unlike other salmonella, the causative agents of typhoid and paratyphoid fever, having penetrated the bloodstream, are able to survive and multiply in phagocytes. They can multiply in the mesenteric lymph nodes, liver and spleen and cause generalization of the process. After the death of phagocytes, Salmonella enters the blood again. In this case, Vi-antigen inhibits bactericidal factors.
When salmonella die, endotoxin is released, which inhibits the activity of the central nervous system (typhoid - from the Greek typhos - fog, confusion) and causes prolonged fever. The action of endotoxin can cause myocarditis, myocardial dystrophy, and infectious and toxic shock.
As a result of bacteremia, generalized infection of the gallbladder, kidneys, liver, bone marrow, and dura maters occurs (secondary localization of Salmonella). Secondary invasion of the intestinal epithelium, especially Peyer's patches, occurs. In the wall sensitized by salmonella, allergic inflammation with the formation of the main dangerous complication - typhoid ulcers. Long-term carriage of Salmonella has been observed in gallbladder with the release of the pathogen in feces, pyelonephritis, bleeding and intestinal perforation when Peyer's patches are affected. Then the formation of post-infectious immunity occurs, elimination of the pathogen and healing of ulcers or the formation of bacterial carriage (in Western Siberia, often against the background of chronic opisthorchiasis).
The causative agents of salmonellosis are other serotypes of salmonella that are pathogenic for humans and animals (S.typhimurium, S.enteritidis, S.heldelberg, S. newport and others). The pathogenesis of salmonellosis is based on the action of the pathogen itself (its interaction with the host body) and endotoxin accumulating in food products, infected with salmonella. In the classic version, Salmonella toxicoinfection is gastroenteritis. However, when the intestinal lymphatic barrier breaks, generalized and extraintestinal forms of salmonellosis can develop (meningitis, pleurisy, endocarditis, arthritis, liver and spleen abscesses, pyelonephritis, etc.). The increase in generalized and extraintestinal forms of salmonellosis is associated with an increase in the number of immunodeficiency states, which is of particular importance in HIV infection.
A separate problem is posed by hospital strains of Salmonella (usually individual phages of S.typhimurium), which cause outbreaks of nosocomial infections mainly among newborns and weakened children. They are transmitted mainly through contact and household contact from sick children and bacteria carriers; they are highly invasive, often causing bacteremia and sepsis. Epidemic strains are characterized by multiple drug resistance (R-plasmids), high resistance, including to high temperatures.
Epidemiological features. Characterized by widespread distribution. The main reservoirs of salmonella are humans (causative agents of typhoid fever and paratyphoid A) and various animals (other serotypes of salmonella). The main pathogens are polypathogenic. The main sources of infection are meat and dairy products, eggs, poultry and fish products. The main routes of transmission are food and water, less often - contact. Characterized by an extreme multiplicity of reservoirs and possible sources of infection. Farm animals and birds are of primary importance.
Laboratory diagnostics. The main method is bacteriological. Based on pathogenesis optimal timing bacteriological research in gastrointestinal forms it is the first days, in generalized forms it is the end of the second - the beginning of the third week of the disease. When studying various materials (stool, blood, urine, bile, vomit, food debris), the highest frequency of positive results is observed in the study of feces; for the causative agent of typhoid fever and paratyphoid fever - blood (blood culture).
Research is carried out according to a standard scheme. The test material is inoculated on dense differential diagnostic media - highly selective (bismuth sulfite agar, brilliant green agar), medium selective (Ploskirev's medium, weakly alkaline agar), low selective (Endo and Levin agars) and in enrichment media. Rapoport medium is used for blood culture. On bismuth-sulfite agar, Salmonella colonies acquire a black (rarely greenish) color. The grown colonies are subcultured onto media for primary (Russell's medium) and biochemical (hydrogen sulfide, urea, glucose, lactose) identification. For preliminary identification, the O1-salmonella phage is used, to which up to 98% of salmonella are sensitive.
To identify cultures in RA, polyvalent and monovalent O-, H- and Vi-antisera are used. First, polyvalent adsorbed O- and H-sera are used, and then the corresponding monovalent O- and H-sera are used. To identify the causative agents of typhoid fever and paratyphoid fever, antibodies to the O2 (S.paratyphi A), O4 (S.paratyphi B), O9 (S.typhi) antigen are used. If the culture is not agglutinated by O-serum, it should be examined with Vi-serum. To quickly detect Salmonella, polyvalent luminescent sera are used.
Serological tests are carried out for diagnosis, as well as detection and differentiation various forms carriers. RA (Widal reaction) is used with O- and H-diagnosticums and RPGA using polyvalent erythrocyte diagnosticums containing polysaccharide antigens of serogroups A, B, C, D and E and Vi-antigen.
Treatment- antibiotics (chloramphenicol, etc.). Antibiotic-resistant strains are often identified. It is necessary to determine the antibiotic resistance of isolated cultures.
Specific prevention can be used primarily against typhoid fever. A chemical sorbed typhoid monovaccine is used. Vaccination is currently used mainly for epidemic indications.
Several billion years ago, tiny living creatures - bacteria - settled on Earth. They for a long time reigned on the planet, but the appearance of plants and animals disrupted the life activity habitual for microorganisms. We should pay tribute to the “kids” who managed to adapt to new conditions. Microorganisms, having settled in food, inside the human body, in water and air, have established very strong contact with humans. What consequences can people expect from interacting with them?
Nutritionists compile tables of proper nutrition, where they indicate the ratio of proteins, fats, calories and carbohydrates in ready-made meals. But there is one more component that is not mentioned there. This is the presence of beneficial bacteria.
The human large intestine contains microorganisms that actively participate in the digestion process. Normal microflora helps strengthen the immune system and increase vital activity. But failures in its operation lead to the fact that a person becomes defenseless against viruses and toxins.
You can support the body's little defenders by eating foods that contain probiotics. They are maximally adapted to the needs of the human body, where they carry out active sanitary activities. What healthy foods include in the diet?.jpg" alt="probiotics and prebiotics" width="300" height="178" srcset="" data-srcset="https://probakterii.ru/wp-content/uploads/2015/08/bakterii-v-produktah3-300x178..jpg 451w" sizes="(max-width: 300px) 100vw, 300px">!}
Varied selection
data-lazy-type="image" data-src="https://probakterii.ru/wp-content/uploads/2015/08/bakterii-v-produktah-300x205.jpg" alt=" fermented cabbage" width="300" height="205" srcset="" data-srcset="https://probakterii.ru/wp-content/uploads/2015/08/bakterii-v-produktah-300x205..jpg 400w" sizes="(max-width: 300px) 100vw, 300px">!}- pills;
- powders;
- capsules;
- suspensions.
A very important component in the diet
It is necessary to specifically focus on the benefits of lactic acid products. Thanks to the presence of lactic acid in it, it neutralizes putrefactive bacilli that want to cause damage to the human body. It is impossible to overestimate the role of lactic acid products in maintaining health. They are very easily digestible, protect the intestinal walls from the invasion of infections, promote the breakdown of carbohydrates and the synthesis of vitamins.
Lactic acid products are a real salvation for people suffering from intolerance to whole milk. Thanks to bifidobacteria, lactose and milk sugar are perfectly digested.
Included fermented milk products contained vitally important elements power supply:
- fats;
- amino acids;
- vitamins;
- proteins;
- carbohydrates;
- calcium.
During the preparation of dairy products, they are synthesized biologically active substances which prevent the appearance of malignant tumors.
The beneficial effects of dairy and fermented milk products can only be felt if they are consumed regularly. A proper diet should include dairy products several times a week. The body absorbs them well in combination with grain dishes containing carbohydrates.
How do pathogenic microbes get into food?
A hot dog or spoiled sausage purchased from a street stand can cause food poisoning, which is accompanied by the following symptoms:
- vomiting, nausea;
- chills;
- stool disorder;
- dizziness;
- weakness;
- stomach ache.
The causative agents of such serious ailments are bacteria. They can be found in raw meat, on the surface of fruits and vegetables. Semi-finished products are often subject to spoilage if storage rules are violated.
Food can become contaminated in food service establishments if workers do not wash their hands after using the toilet. Dishes displayed on display also run the risk of spoilage. After all, visitors may sneeze or cough while choosing their food.
Rodents, birds, and domestic animals often become carriers of diseases. When they come into contact with human food, they can contaminate it.
Pathogenic bacteria that cause poisoning multiply very quickly on the surface of tables, cutting boards, and knives. During the cooking process, crumbs remain on kitchen equipment, which are an excellent breeding ground for microbes, which causes food spoilage.
Protect yourself
Ideal conditions for bacterial growth are:
- moisture – required condition for life;
- heat - develops well at room temperature;
- time – the number doubles every 20 minutes.
Food left at room temperature for long periods of time is an ideal environment for microbes to feed and multiply. Heated dishes can be consumed within 2 hours without harm to health, but reheating them is not recommended.
Spoilage of dairy products is indicated by a bitter taste and increased gas formation. If storage rules are violated, putrefactive microbes actively work to decompose the protein. Do not consume spoiled products, and especially do not risk giving them to children.
To protect yourself from serious illness, store raw and prepared foods separately in the refrigerator. Don't forget that food should be stored in special food containers with lids. In the absence of such containers, you can simply cover the finished dishes with cling film.
Be sure to wash your hands before preparing food. Treat work surfaces and equipment with special disinfectant solutions or boiling water..jpg" alt=" hand washing" width="300" height="199" srcset="" data-srcset="https://probakterii.ru/wp-content/uploads/2015/08/istochnik-bakterij4-300x199..jpg 746w" sizes="(max-width: 300px) 100vw, 300px">!}
Food must be defrosted until completely thawed. Otherwise, they will not undergo complete heat treatment. This means that pathogenic bacteria can multiply unhindered.
Leftover food can be stored for no more than two days. And only in the refrigerator. When preparing salads, it is strictly forbidden to add yesterday's surplus to them.
We choose wisely
When choosing fermented milk products in a store, carefully study the label. It contains information about the amount of fats, carbohydrates, proteins, and vitamins.
Pay attention to the shelf life: if the product does not spoil for more than two days, then it most likely does not contain live bacteria.
Choose natural products made from whole milk, rather than vegetable fats and starch, which are harmful to the body. Of course, it also contains fats and carbohydrates, but there are definitely no beneficial microorganisms there.
Interaction with bacteria in Everyday life can bring great benefit to a person or irreparable damage. Therefore, you should never let your guard down. Don't be tempted to eat cream cakes sold right on the street under scorching heat. sun rays. Better go to the store and buy live yogurt (just wash your hands before eating!). And then your body will definitely thank you with excellent health and active life.
Microorganisms. At the ends of the sticks, inclusions in the form of beads and granules are usually visible. Chains of bacteria are often formed, sometimes branched. A characteristic property of mycobacteria is acid, alcohol and alkali resistance (see Acid-resistant bacteria), associated with the accumulation of wax-like substances in the cell and the special structure of the cell membrane. Mycobacteria are cultivated on enriched solid media with the addition of eggs, milk, potatoes and on liquid synthetic media with the addition of albumin. Mycobacteria include the causative agents of tuberculosis,.
According to Bergey (D. Bergey, 1957), pathogenic representatives of mycobacteria include seven species: M. tuberculosis hominis, M. tub. bovis, M. tub. avium, M. microti, M. para tuberculosis, M. leprae hominis, M. lep. murium. IN Lately The pathogenic group of mycobacteria includes the 8th species - M. ulcerans. Mycobacteria of this species grow at temperatures no higher than 33°, were isolated from ulcerative lesions of the lower extremities of humans, and experimentally cause skin lesions in mice and rats. A special potentially pathogenic group consists of mycobacteria isolated from skin lesions of humans, cattle, cold-blooded animals - fish, snakes, etc., and from soil. The main representatives of the group - M. fortuitum, M. marinum, M. thamnopheos, M. platypoecilus - grow at a temperature of 10-20-25°; not pathogenic for pigs, rabbits, mice.
True saprophytes are morphologically and tinctorially similar to pathogenic mycobacteria, but they are more polymorphic, relatively acid-resistant, and weakly alkali- and alcohol-resistant. They grow quickly on regular and special media at a temperature of 10-20°. The main representatives of saprophytes: M. phlei (Timothy grass stick) - grows at a temperature of 28-52° in the form of a soft grayish or yellow color, forming folds during aging; M. smegmatis - polymorphic, relatively short rods, grow for 2-4 days on all media at a temperature of 28-45° in the form of a juicy, oily creamy coating, sometimes dry. Both species are not pathogenic for experimental animals.
A special heterogeneous group consists of the so-called atypical, or abnormal, unclassified mycobacteria. Their nature and significance in human pathology have not been precisely clarified. They are isolated relatively rarely from material from people suffering from tuberculosis or clinically similar diseases (“mycobacteriosis” of the lungs, pleura, lymph nodes, joints, etc.). The division of “anonymous” mycobacteria into 4 groups has been temporarily accepted: 1) photochromogenic mycobacteria (Kansas type); their cultures, usually without pigment, when grown in the dark, even with short exposure to light, acquire a lemon-yellow color; 2) scotochromogenic mycobacteria - cultures orange color when growing in the dark; 3) non-photochromogenic, non-pigmented mycobacteria - grayish, pale yellow, do not produce pigment when exposed to light; 4) growing quickly at room temperature. On solid media, atypical mycobacteria form a smooth, finely folded, often oily coating; on liquid media, they grow at the bottom in the form of flakes, and on the surface of the medium - in the form of a thin oily film. The cells of atypical mycobacteria are polymorphic, grow on different nutrient substrates at a temperature of 20-37-38°, and do not form “bundles”. Most strains are neither pathogenic nor virulent for guinea pigs and rabbits, some, especially photochromogenic ones, are virulent in significant doses for white mice when administered intravenously (0.5-1 mg) and for golden hamsters when administered intraperitoneally (1-10 mg). Acid resistant; are stained red according to Ziehl-Neelsen. They have pronounced catalase activity, for the most part are primarily resistant to such anti-tuberculosis drugs (see) as tubazide, sodium para-aminosalicylate. Tuberculin reactions in humans and experimental animals suffering from “mycobacteriosis” are inconsistent.
Mycobacterium tuberculosis - see Tuberculosis.
Mycobacteria.
In the genus Mycobacterium families Mycobacteriaceae included acid- and alcohol-resistant aerobic immobile gram-positive straight or curved rod-shaped bacteria. Sometimes they form filamentous or mycelial structures. Characterized by a high content of lipids and waxes (up to 60%). Catalase- and arylsulfatase-positive, resistant to lysozyme. They grow slowly or very slowly.
Mycobacteria are widespread in the environment - water, soil, plants and animals.
On the basis of pathogenicity they distinguish themselves pathogenic, causing specific diseases ( 5 groups - M. Tuberculosis, M. leprae, M.bovis, M. Miccroti, M. Lepraemurium) and atypical mycobacteria.
Pathogenic mycobacteria.
Mycobacterium Tuberculosis (Koch's wand). The causative agent of human tuberculosis is a chronic infectious disease characterized by damage to the respiratory system, bones, joints, skin, genitourinary and some other organs. The disease has been known since ancient times. The pulmonary form of tuberculosis was described by ancient authors (Arteus of Cappadocia, Hippocrates, etc.) However, the ancient authors did not consider it as an infection; Ibn Sina considered it a hereditary disease. Fracastoro was the first to directly point out its infectious nature, and Silvius noted the connection of pulmonary tubercles with consumption. The variety of clinical manifestations of tuberculosis led to many erroneous ideas: de Laaeneck attributed pulmonary tubercles to malignant neoplasms, Virchow did not connect caseous necrosis with the tuberculous process. The growth of cities, crowded population and low sanitary standard of living led to the fact that in the 18th and 19th centuries. tuberculosis was gathering a bountiful harvest among different segments of the population: just remember Mozart, Chopin, Nekrasov, Chekhov and others.
The infectious nature of the disease was proven by Wilmain (1865), and the most important stage in the study and improvement of measures to combat tuberculosis was Koch’s short report at a meeting of the Berlin Physiological Society on March 24, 1882 on the etiology of tuberculosis, in which he outlined the main postulates-criteria for assessing the pathogenicity of any microorganism
Epidemiology. Storage tank Mycobacterium Tuberculosis - a sick person, the main route of infection is aerogenic, less often through the skin and mucous membranes. In rare cases, transplacental infection of the fetus is possible.
A) The penetration of mycobacteria does not always cause the development of a pathological process; unfavorable living and working conditions play a special role. Currently, there is an increase in morbidity, which is associated with an obvious decrease in the standard of living of the population and the accompanying imbalance in nutrition on the one hand, and the “activity” of the pathogen is increasing, apparently due to the displacement of natural competitors as a result of the use of antimicrobial agents.
b) Of no less importance are the “aging” of the population around the world and the increase in the number of people with chronic diseases accompanied by impaired immunity.
V) special role in infection Mycobacterium Tuberculosis The overcrowding of the population plays a role: in the Russian Federation there are pre-trial detention centers, refugee camps, and “homeless” people.
Morphology and tinctorial properties.
Thin, straight or slightly curved rods measuring 1-10 * 0.2-0.6 µm, with slightly curved ends, contain granular formations in the cytoplasm. Morphology varies depending on the age of the culture and cultivation conditions - in young cultures the rods are longer, and in old ones they tend to simple branching. Sometimes they form coccoid structures And L-forms, retaining infectiousness, as well as filterable forms.
Motile, do not form spores, lack capsules, but have a microcapsule separated from the cell wall by an osmiephobic zone. Acid resistant which is due to the high content of lipids and mycolic acid in the cell wall, and also form acid-stable granules, predominantly consisting of metaphosphate ( Mucha grains), located freely or in the cytoplasm of rods.
Gram-positive, aniline dyes are poorly perceived, according to Ziehl-Neelsen they are colored bright red, according to Muh-Weiss - violet (iodophilicity).
Cultural properties. Aerobes, but are able to grow in facultative anaerobic conditions, 5-10% CO2 content promotes faster growth. They reproduce by division, the process occurs very slowly, on average in 14-18 hours. Temperature optimum 37-38 degrees C, pH 7.0-7.2
(grows within 4.5–8.0).
For growth, it requires the presence of a protein substrate and glycerol, as well as carbon, chlorine, phosphorus, nitrogen, growth factors (biotin, nicotinic acid, riboflavin), and ions (Mg, K, Na, Fe).
For cultivation, dense egg media (Lewinstein-Jensen, Petragnani, Doce), synthetic and semi-synthetic liquid media (Soton's medium) are used. In liquid media, growth is observed on days 5-7 in the form of a dry, wrinkled film (R - shape) rising to the edges of the test tube; the medium remains transparent. In media containing detergent (Tween-80) they produce uniform growth throughout the thickness of the medium. In liquid media and during intracellular development, a characteristic cord factor ( trehalose-6,6-dimikolate), which causes the convergence of bacterial cells in microcolonies, their growth in the form of serpentine braids and is related to the virulence of the pathogen. On solid media, growth is noted on days 14-40 in the form of a dry, wrinkled, cream-colored coating; colonies with a raised center, reminiscent of cauliflower, are crumbly, poorly wetted with water and have a pleasant aroma. Cultures are difficult to remove from the medium, and when pierced they crack. Under the influence of antibacterial drugs, they can dissociate to form soft, moist S-colonies or grow in the form of smooth or pigmented colonies. Distinctive feature Mycobacterium Tuberculosis - ability to synthesize a significant amount of nicotinic acid (niacin), which is used for its differential diagnosis with other mycobacteria (niacin test), one of the conditions is the need to inoculate on Levinstein-Jensen medium, which does not contain malachite green) because the dye reacts with the reagents used). On media with bile it forms a grayish, oily coating formed by elongated branching rods.
Koch stick It is quite resistant to various influences, it dies in milk after 15-20 minutes at a temperature of 60 degrees C, at a similar temperature it persists in sputum for up to an hour, and when boiled it dies after 5 minutes. Direct sunlight kills Koch's wand in 45-55 minutes, diffused light - in 8-10 days. Keeps well when dried (up to several weeks). Conventional chemical disinfectants are relatively ineffective; a 5% phenol solution kills Mycobacterium Tuberculosis only after 5-6 hours, the pathogen is also able to quickly develop resistance to many antibacterial agents.
Pathogenesis of lesions and clinical manifestations.
A) Most often, infection occurs through inhalation of an aerosol containing mycobacteria, or through consumption of contaminated products (penetration through the skin and mucous membranes is possible). Inhaled mycobacteria phagocytose alveolar and pulmonary macrophages and transport them to regional lymph nodes; phagocytic reactions are incomplete and the pathogen survives in the cytoplasm of macrophages. The ability to reduce the activity of phagocytes is determined by sulfatides, which enhance the toxic effect of cord factor and inhibit phagosomal-lysosomal fusion. The inflammatory response is usually not expressed, which is largely mediated by the ability of the cord factor to inhibit the migration of polymorphonuclear phagocytes. At the site of penetration it may develop primary affect. In dynamics, along the regional lymphatic tracts and nodes, a primary complex is formed, characterized by the development of granulomas in the form of tubercles (hence tubercle, or tuberculosis).
the formation of granulomas has no characteristic features and is a cellular reaction of DTH. Sensitization of the body is caused by the action of a number of mycobacterial products known as old Koch tuberculin, which exhibits local and systemic effects. To a certain extent, the formation of granulomas is promoted by the formation of lactic acid, low pH, and high CO2 concentration. In the center of each tubercle there is an area of cheesy necrosis, where the Koch bacillus is located. The area of necrosis is surrounded by epithelioid and Pirogov-Langhans giant cells. The center is surrounded by epithelioid cells, and along the perimeter there are lymphocytes, plasma cells and mononuclear cells; the primary focus is most often observed in the lungs (Ghon's focus). In granulomas, the reproduction of the pathogen usually slows down or stops altogether.
Quite characteristic " period of latent microbiism"- a condition in which infiltrated mycobacteria do not cause the development of inflammatory reactions and freely disseminate throughout the body.
In most cases, primary lesions heal completely
degradation of the contents, its calcification and fibrosis
parenchyma.
Clinical manifestations are usually absent or resemble a flu-like syndrome; sometimes the primary focus or enlarged bronchopulmonary lymph nodes can be detected x-ray.
Primary tuberculosis is characterized by high tissue sensitivity to mycobacterial metabolites, which contributes to their sensitization during healing of the affect increased sensitivity disappears and the severity of immune reactions increases. However, under these conditions, it is possible for the pathogen to disseminate from primary foci and form screening foci; they are usually localized in the lungs, kidneys, genitals and bones.
b) When the body's immunity is weakened, the lesions become more active and progress with the development of a secondary process. A certain contribution to the pathogenesis is made by sensitization of the body, causing a variety of toxic-allergic reactions in the patient.
reactivation occurs 20-25 years after the initial infection. It is usually provoked by stress, nutritional disorders and general weakening of the body. Cavities form in the lungs, bronchi and small vessels, from which necrotic curd masses containing significant amounts of the pathogen are actively expectorated.
Clinically, reactive tuberculosis is manifested by cough, frequent hemoptysis, weight loss, profuse night sweats, and chronic low-grade fever.
V) In more rare cases, in weakened adolescents and adults, as well as in patients with immunodeficiencies, it is observed disseminated (miliary) tuberculosis, characterized by the formation of granulomas in various organs.
the development of generalized lesions often occurs after the contents of the granuloma break through into the bloodstream.
General manifestations are similar to those of secondary tuberculosis, but they are often accompanied by lesions of the brain and its membranes; the prognosis of this form is the most unfavorable.
The variety of forms made its classification difficult.
Currently, the clinical classification identifies three main forms:
Tuberculosis intoxication in children and adolescents.
Tuberculosis of the respiratory system, including the primary complex, damage to the internal lymph nodes, pleura, upper respiratory tract, focal, infiltrative, cavernous, fibrous-cavernous, cirrhotic pulmonary tuberculosis, tuberculoma, etc.
Tuberculosis of other organs and systems, including lesions of the meninges, eyes, joints and bones, intestines and peritoneum, skin and subcutaneous tissue. Organs of the genitourinary system, etc.
Laboratory diagnostics.
Includes methods included in the mandatory diagnostic minimum and additional research methods.
A). In case of illness – microscopy of pathological material(sputum, fistula discharge, urine, lavage water from the bronchi) in Ziehl-Neelsen stained smears, red acid-fast bacilli can be detected. (In recent years, the Murahashi-Yoshida method has been introduced, which allows differentiating dead and living bacteria).
when the pathogen content is insignificant, the Ulengut accumulation method is used - the material is mixed with an equal or double volume of NaCl and NaOH, shaken and incubated for 30 minutes at a temperature of 21 degrees C. Then cell detritus and foreign bacteria are removed by centrifugation, the sediment is neutralized with a 30% acetic acid solution, and smears are prepared and stained using Ztlu-Neelsen or Kinyon.
The flotation method is more effective - a solution of NaOH, distillate, xylene (benzene) is added to the material and shaken vigorously, the resulting foam floats up and captures mycobacteria, it is sucked off and smears are prepared.
Quantitative assessment of the mycobacteria population by the Haffka-Steenken method (counting bacteria on calibrated glasses in certain fields of view) has a certain value in assessing the severity of the process, the effectiveness of treatment and the prognosis of the disease.
The most effective bacterioscopic method is fluorescence microscopy, because staining with a fluorochrome (for example, auramine-rhodamine) makes it possible to detect even a small amount of mycobacteria (stained white-yellow), as well as forms with altered cultural and tinctorial properties.
B) Isolation of the pathogen. Before sowing, the test material can be treated according to Ulengut or Sumiyoshi (15-20% solution of HCl or H2SO4), the test samples are centrifuged, washed with saline and inoculated, thoroughly rubbed onto solid nutrient media (usually Levinstein-Jensen). For simplicity, samples can be treated with various antibiotics that inhibit the growth of contaminating flora.
The disadvantage of the method is the duration of obtaining results – from 2 to 12 weeks.
The advantage is the possibility of obtaining a pure culture, which allows it to be identified, virulent properties assessed, and sensitivity to drugs determined.
Accelerated methods for isolating the pathogen have been developed (Price), the material is placed on a glass slide, treated with H2SO4, washed with saline and added to a nutrient medium supplemented with citrated blood. The glass is removed after 3-4 days and stained according to Ziehl-Neelsen.
- “Gold standard” - in the diagnosis of tuberculosis - biological test on guinea pigs, infected subcutaneously or intraperitoneally with 1 ml of material obtained from the patient. Animals develop a generalized infection leading to death after 1-2 months, but the disease can be recognized earlier by testing with tuberculin - after 3-4 weeks, and lymphadenitis already after 5-10 days. The paragraphs contain them a large number of bacteria. However, the emergence of resistant and modified mycobacteria has reduced the sensitivity of this test. To increase it, intratesticular infection is used, or the immunity of animals is suppressed by introducing glucocorticoids.
