Detailed description of the study
The study aims to diagnose respiratory tuberculosis, a multisystem disease with multiple manifestations that is the most common cause of infectious disease mortality worldwide. According to WHO, in 2015 there were 1.4 million deaths from tuberculosis, of which 0.4 million people had HIV.
Russia is one of the countries with the highest prevalence of tuberculosis, although over the past 10 years a positive trend has been observed in this direction: the number of new cases of infection and the proportion of carriers out of the total number of patients are decreasing. As a rule, this disease affects the lungs (85% of cases), but can also affect other organs, including bones. Sources of infection are sick people with an open form of the disease - releasing the pathogen into the environment with saliva.
Symptoms of the disease are:
- Weight loss/anorexia;
- Loss of appetite;
- Profuse sweating at night;
- Heat;
- General weakness.
If we are talking about the pulmonary form of the disease, symptoms may include:
- Cough;
- Hemoptysis (coughing up blood);
- Chest pain.
In the extrapulmonary form, symptoms will depend on the area of the lesion.
Mycobacterium tuberculosis complex is the common name for closely related bacteria that cause tuberculosis. They have many pathogenicity factors that allow them to survive for a long time in the environment and evade the immune response. Mycobacterium tuberculosis is an intracellular parasite, thus, being absorbed by the cells of the immune system, the pathogen inactivates the enzymes of these cells, remaining viable. Thanks to these properties, Mycobacterium tuberculosis is a rather dangerous disease, especially for people with weakened immune systems. Infection usually occurs through airborne droplets when an infected person sneezes or coughs; in rare cases, even a conversation with a sick person is enough for infection. Also, tuberculosis can be transmitted even from a pregnant woman to her fetus while still in the womb.
Polymerase chain reaction (PCR) is a research method that allows you to detect pathogen DNA in biomaterial even in small quantities. PCR for M. Tuberculosis, according to international clinical guidelines, is not the standard for diagnosing this disease. This test is used as an additional test. “Gold standard”: Mantoux test, T-SPOT, Diaskin or Quantiferon test.
MYCOBACTERIA
MYCOBACTERIA
(
Mycobacterium
, singular; Greek, mykes fungus + bacteria) - gram-positive acid- and alkali-resistant bacteria belonging to the genus Mycobacterium (Lehmann, Neumann 1896), family. Mycobacteriaceae, order Actinomycetales. N. A. Krasilnikov (1938, 1949) to the seventh. Mycobacteriaceae includes the genus Mycococcus; in Bergey's Guide to Bacteria (D. Bergey, 1974) it is assigned to other families. The genus Mycobacterium includes St. 100 species of M., widely distributed in nature (soil, water, manure, cereals, food products); Among them there are species that are pathogenic for humans and animals. M. cells are rod-shaped, 0.2-0.6 microns wide and 1.0-10 microns long, or granular, sometimes in the form of branching threads, which are easily fragmented into rods or cocci; at certain stages of growth, they are acid- and alkali-resistant, gram-positive, immobile, and do not form spores or capsules. Strains of saprophytes grow on simple nutrient media; pathogenic M. require complex media; some M. are characterized by intracellular parasitism. M. are characterized by a high lipid content. They differ in amidase, catalase and other types of enzyme activity; They are aerobes, but can grow deep in nutrient media. They form different types of colonies (B- and S-forms) of white, cream, yellow or orange color due to carotene pigment, the appearance of which may be associated with the action of light. Fast-growing M. form colonies up to 7-14 days, slow-growing ones - up to 8 weeks. at t° 30-40°. Individual saprophytes grow at a temperature of 52° or 10°. Pathogenic M. include: M. tuberculosis, M. bovis, M microti, M. paratuberculosis, M. africanum, M. leprae, M. lepraemurium.
M. tuberculosis - M. human tuberculosis (M. tuberculosis Lehmann, Neumann 1896; synonym: M. tuberculosis typus humanus Lehmann, Neumann 1907, M. tuberculosis var. hominis Bergey 1934). Burgee's Guide to Bacteria (1974) provides a description of the strain H37 Rv. Strictly acid and alkali resistant. Growth is slow at t° 37°, possible at t° 30-34°. Optimum pH 6.4-7.0. More abundant and rapid growth on media with glycerol. Causes a reduction of nitrates, niacin-positive, catalase activity is lost when heated to t° 68°. M. tuberculosis causes tuberculosis in humans and great apes, as well as in animals that come into contact with humans.
A dose of the pathogen of 0.01 mg is highly pathogenic for guinea pigs and hamsters, less pathogenic for rabbits, cats, goats, cattle and poultry. To infect mice, doses of the pathogen of 0.001 - 1 mg are used. M. with lower virulence are isolated from patients with tuberculous lupus and genitourinary tuberculosis. Infected animals, as well as humans, exhibit delayed hypersensitivity to tuberculin obtained from tuberculosis pathogens and less sensitivity to tuberculin preparations from other types of M. - sensitins. The antigenic structure of M. tuberculosis is close to M. bovis, M. microti and M. kansasii.
M. bovis—M. bovine tuberculosis (M. bovis Karlson, Lessel 1970); synonym: M. tuberculosis typus bovinus Lehmann, Neumann 1907, M. tuberculosis var. bovis Bergey et al. 1934). Primary isolated cultures grow poorly on media with glycerol, colonies are without pigments, the test for niacin is negative. Strains resistant to isoniazid lack catalase activity, some of them are resistant to para-aminosalicylic acid. They cause tuberculosis in cattle, people, carnivores, pigs, parrots and some birds of prey. Highly pathogenic for rabbits, guinea pigs, calves; moderately pathogenic for hamsters and mice; weakly pathogenic for dogs, cats, horses and rats; non-pathogenic for most birds. Certain strains isolated from patients with lupus and scrofuloderma have low pathogenicity for animals. Tuberculins prepared from M. tuberculosis and M. bovis are almost identical in their action. Bacteria Calmette-Guérin (BCG) have the same properties as M. bovis, but are more attenuated and grow well on media containing glycerol.
M. microti - M. vole mice (M. microti Beed 1957; synonym: M. tuberculosis var. muris Brooke 1941, Vole bacillus Wells 1937). They grow on glycerin media at a temperature of 37° for 28-60 days. They cause generalized tuberculosis in voles, local lesions in guinea pigs, rabbits, and calves. According to immunol, the characteristics are closest to M. tuberculosis and M. bovis.
M. paratuberculosis - M. paratuberculosis of cattle (M. paratuberculosis Bergey et al. 1923, syn. Johne's bacillus). Require special growth factors. For the first time, it was possible to obtain growth on media with killed acid-fast bacteria. They are also cultivated on synthetic media. Causes hypertrophic enteritis in cattle. Non-pathogenic for guinea pigs, rats, mice; Only in very large doses can they cause minor local nodular lesions. They have four antigens in common with M. avium and five with M. tuberculosis.
M. africanum - Mycobacterium africanum (M. africanum Castets, Rist, Boisvert 1969). They grow at a temperature of 37° on egg and agar media with bovine serum. Isolated from tuberculosis patients in tropical Africa. Pathogenic to guinea pigs, mice and partly rabbits.
M. leprae - M. human leprae (M. leprae Lehmann, Neumann 1896; synonym: Leprosy bacillus, Hansen's bacillus). An obligate intracellular parasite of humans, does not grow on nutrient media, and is strictly acid-resistant. A leprosy-like disease was induced using an immunosuppressive mouse model.
M. lepraemurium - M. rat lepra (M. leprae murium Marchoux, Sorel 1912). They do not grow on nutrient media; in experiments they are transferred to rats, mice, and hamsters. They cause endemicity among rats and cutaneous nodular lesions in other animals.
In nature, there is an extensive group of opportunistic M., which cause mycobacteriosis. Specific therapy for tuberculosis and mycobacteriosis is different, and therefore identification of the pathogen is of particular importance. If for the purposes of taxonomy and identifying genetic relationships between representatives of the genus M. more than 100 tests and their complexes have been proposed, then the classification version developed by Runyon (E. Runyon, 1959, 1965) is convenient for practical use. Conditionally pathogenic and saprophytic M., called atypical by the author, are divided into 4 groups according to a limited number of characteristics - growth rate, pigment formation, colony morphology, some cultural-biochemical. indicators.
Group I - photochromogenic: M. kansasii, var. luciflavum, var. aurancicum, var. album. The main sign is the appearance of pigment in the light. Colonies from S- to RS-form contain carotene crystals, coloring them yellow; There are cultures lacking pigment. Growth rate from 7 to 20 days at t° 37°; usually strictly catalase positive. Isolated from people with lung lesions similar to tuberculosis.
Group II - scotochromogenic: M. marianum, M. aqua, M. flavescens.
Acid-resistant sticks; form yellow colonies in the dark and orange or reddish colonies in the light, usually S-form; growth is slow at t° 37°. The scotochromogenic opportunistic species M. gordonae and M. scrofulaceum according to the indicated characteristics are close to the saprophytes of this group - M. flavescens and M. aqua, differ from them in resistance to 5% NaCl solution, Tween-80 hydrolysis, and nitrate reduction . Pathogenicity for humans and lab. animals is insignificant. Sometimes they cause lymphadenitis in children. Isolated from contaminated water bodies and soil.
Group III - non-chromogenic: M. avium (intracellulare, battey, Bataglini ulcerans), M. gastri, M. terrae, M. xenopi. Acid-fast rods, S- or SR- and R-form colonies; usually colorless. M. avium and M. intracellulare are distinguished by serological characteristics; there are 23 serotypes in this complex. M. avium gives a negative test for arylsulfatose, while M. intracellulare and other representatives of this group test positive. Opportunistic species differ from saprophytes in their resistance to 5% sodium chloride solution and Tween-80 hydrolysis. Pathogenic for birds, less pathogenic for cattle, pigs, sheep, dogs. They are isolated from sick animals, water and soil.
Group IV - fast growing: M. marinum, M. fortuitum, M. phlei, M. smegmatis, M. borstelense, M. vaccae, M. thamnopheos. Growth from 1-2 to 14 days, possible at temperatures above 45° (M. smegmatis), R- or S-form colonies. Scotochromogenic and photochromogenic strains of this group are rarely isolated from patol, patient material, but some of them have a wedge, significance.
The role of atypical M. as pathogens became known at the beginning of the century. In different regions of the world, their isolation from people ranges from a few cases to 20-42% (M. P. Zykov, 1966, etc.). OK. 1/3 of mycobacteriosis is caused by M. kansasii (group I), then M. avium and M. intracellulare (group III) and representatives of group IV (M. fortuitum, M. borstelense, etc.). Group II has the least pathogenetic significance. Non-tuberculous M. can be isolated from healthy individuals and from patients with tuberculosis. To diagnose mycobacteriosis, as well as to study the infection of the population with opportunistic M., allergy tests with sensitins are used. Due to the resistance of many M. to antibiotics and other medicinal substances, the use of this criterion for identifying strains is considered unreliable, as well as virulence tests for labs. animals.
See also Leprosy, etiology; Tuberculosis, etiology.
Bibliography:
Zykov M. P. and Ilyina T. B. Potentially pathogenic mycobacteria and laboratory diagnosis of mycobacteriosis, M., 1978, bibliogr.; Lazovskaya A. L. and Blokhina I. N. Pathogenic and opportunistic mycobacteria, Gorky, 1976, bibliogr.; Yablokova T. B. et al. Assessment of the diagnostic value of sensitins in experiment and clinic, Problems, tub., No. 7, p. 62, 1977, bibliogr.; A typical mycobacteria, ed. by JG Weiszfeiler, Budapest, 1973; Bergey's manual of determinative bacteriology, ed. by RE Buchanan a. NE Gibbons, Baltimore, 1975; R un on E.N. Typical mycobacteria, Their classification, Amer. Rev. resp. Dis., v. 91, p. 288, 1965.
T. B. Yablokova.
References
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