Non-tuberculous mycobacteria
Last reviewed: 23.04.2024
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Non-tuberculosis mycobacteria are independent species widely distributed in the environment, such as saprophytes, which in some cases can cause serious diseases - mycobacteriosis. They are also called environmental mycobacteria (environmental micabacteria), mycobacteriosis pathogens, opportunistic and atypical mycobacteria. The essential difference between non-tuberculosis mycobacteria and mycobacterium tuberculosis complex is that they are practically not transmitted from person to person.
Non-tuberculosis mycobacteria are divided into 4 guppies by a limited number of signs: growth rates, pigment formation, colony morphology, and biochemical properties.
Group 1 - slowly growing photochromogenic (M. Kansasii, etc.). The main sign of representatives of this group is the appearance of pigment in the light. They form colonies from S to RS forms, contain carotene crystals, which color them in yellow. The growth rate from 7 to 20 days at 25, 37 and 40 ° C, catadase-positive.
M. Kansasii - yellow bacilli, live in water, soil, most often affect the lungs. These bacteria can be identified due to their large size and cross-shaped arrangement. An important manifestation of infections caused by M. Kansasii is the development of disseminated disease. Possible lesions of the skin and soft tissues, the development of tenosynovitis, osteomyelitis, lymphadenitis, pericarditis and infections of the urogenital tract.
2 nd group - slow growing scotochromogenic (M. Scrofulaceum, M. Matmoense, M. Gordonae, etc.). Microorganisms form II dark yellow, and in light orange or reddish colonies, usually S-form colonies, grow at 37 ° C. This is the largest group of nontuberculous mycobacteria. They stand out from contaminated reservoirs and soil a and have little pathogenicity for humans and animals.
M. Scrofulaceum (from English scrofula - scrofula) - one of the main causes of cervical lymphadenitis in children under 5 years. In the presence of severe concomitant diseases, they can cause damage to the lungs, bones and soft tissues. In addition to water and soil, microbes are isolated from raw milk and other dairy products.
M. Maimoense - microaerophiles, form grayish-white smooth shiny opaque dome-shaped round colonies.
Primary isolates grow very slowly at 22-37 ° C. Their exposure to light does not cause the production of pigment, If necessary, the exposure continues up to 12 weeks. In humans, they cause chronic lung diseases.
M. Gordonae - the most common recognized saprophytes, scotochromogens of water-propellant water, mycobacteriosis is extremely rare. In addition to water (known as M. Aquae), they are often isolated from soil, gastric washings, bronchial secretions or other material from patients, but in most cases they are non-pathogenic to humans. At the same time, there are reports of cases of meningitis, peritonitis and skin lesions caused by this type of mycobacteria.
The third group is slow growing nonchromogenic mycobacteria (M. Avium complex, M. Gaslri M. Terrae complex, etc.). They form colorless S- or SR- and R-forms of colonies, which can have light yellow and cream shades. They stand out from sick animals, from water and soil.
M. Avium - M. Inlracellulare are combined into one M. Avium complex because their interspecific differentiation presents certain difficulties. Microorganisms grow at 25-45 ° C, pathogenic for birds, less pathogenic for cattle, pigs, sheep, dogs and are not pathogenic for guinea pigs. Most often, these microorganisms cause a lung injury in a person. Defects of the skin, muscle tissue and bone skeleton, as well as disseminated forms of diseases are described. They are among the causative agents of opportunistic infections complicating the acquired immunodeficiency syndrome (AIDS). M. Avium subspecies of paratuberculosis is the causative agent of Jones disease in cattle and, possibly, Crohn's disease (chronic inflammatory disease of the gastrointestinal tract) in humans. The microbe is present in meat, milk and feces of infected cows, and is also found in water and soil. Standard water purification methods do not inactivate this microbe.
M. Xenopi causes lung damage in humans and disseminated forms of AIDS-related diseases. They are separated from frogs of the genus Xenopus. Bacteria form small, smooth, shiny surfaces that are not pigmented colonies, which are subsequently colored in a bright yellow color. Thermophiles do not grow at 22 ° C and give good growth at 37 and 45 ° C. At a bacterioscopy look like very thin sticks, tapering from one end and located parallel to each other (and a kind of palisade). They are often isolated from cold and hot tap water, including drinking water stored in hospital tanks (nosocomial outbreaks). Unlike other conditionally pathogenic mycobacteria, they are sensitive to the action of most anti-tuberculosis drugs.
M. Ukerans - etiological agent of mycobacterial cutaneous N (Buruli ulcer), grows only at 30-33 ° C, Colony growth occurs only after 7 weeks. Excretion of the pathogen also occurs when the mice are infected in the flesh of the sole of the foot. This disease is common in Australia and Africa. The source of infection is the tropical environment and vaccination with BCG vaccine from this mycobacteriosis.
The 4th group is fast-growing mycobacteria (M. Fortuitum complex, M. Phlei, M. Xmegmatis, etc.). Their growth is noted in the form of R- or S-forms of colonies for 1-2 to 7 days. They are found in water, soil, sewage and are representative of the normal microflora of the human body. Bacteria of this group are rarely isolated from pathological material from patients, but some of them are of clinical importance.
M. Fortuitum complex includes M. Fortuitum and M. Chcionae, which consist of subspecies. They cause disseminated processes, skin and postoperative infections, lung diseases. The microbes of this complex are highly resistant to anti-tuberculosis drugs.
M smegmatis - a representative of normal microflora, stands out from the smegma in men. It grows well at 45 ° C. As a causative agent of human diseases, it ranks second among fast-growing mycobacteria after the M. Fortuitum complex. It affects the skin and soft tissues. The causative agents of tuberculosis must be differentiated from M. Smegmatis in the study of urine.
The most common mycobacteriosis is caused by representatives of the 3rd and 1st groups.
[Epidemiology of Mycobacterioses
Mycobacteriosis pathogens are widespread in nature. They can be found in soil, dust, peat, mud, water of rivers, reservoirs and swimming pools. They are found in mites and fish, cause diseases in birds, wild and domestic animals, are representatives of the normal microflora of the mucous membranes of the upper respiratory tract and the urinary tract in humans. Infection with non-tuberculosis mycobacteria occurs from the environment aerogenously, by contact with damage to the skin, as well as food and waterways. The transfer of microorganisms from person to person is uncharacteristic. This conditionally pathogenic bacteria, so the great importance in the emergence of the disease have a decrease in the resistance of the macroorganism, its genetic predisposition. In the affected areas, granulomas are formed. In severe cases, phagocytosis is incomplete, bacteremia is expressed, and in the organs are determined macrophages filled with nontuberculous mycobacteria and resembling leprosy cells.
Symptoms of Mycobacterioses
Symptoms of mycobacteriosis are diverse. Most often the respiratory system is affected. The symptomatology of pulmonary pathology is similar to that of tuberculosis. However, cases of extrapulmonary localization of the process involving skin and subcutaneous tissue, wound surfaces, lymph nodes, genitourinary organs, bones and joints, as well as meninges are not uncommon. Organ damage can begin both acutely and secretly, but almost always proceed painfully,
It is also possible to develop a mixed infection (mixt-infection), in a number of cases they can cause the development of a secondary endogenous infection.
Microbiological diagnosis of mycobacteriosis
The main method of diagnosis of mycobacteriosis bacteriological. Material for the study is taken, based on the pathogenesis and clinical manifestations of the disease. Initially, the question of the belonging of the isolated pure culture to the causative agents of tuberculosis or non-tuberculous mycobacteria is solved. Then a set of studies is used to determine the type of mycobacteria, the degree of virulence, and the Runyon group. Primary identification is based on such characteristics as growth rate, ability to form pigment, morphology of colonies and the ability to grow at different temperatures. To identify these signs, no additional equipment and reagents are needed, so they can be used in the basic laboratories of TB dispensaries. Final identification (reference-identification) with the use of complex biochemical studies is carried out in specialized moratoriums of scientific institutions. In most cases, preference is given to their identification by biochemical facts, such as modern molecular genetic methods are labor-intensive, have many preparatory stages, require special equipment, expensive. Of great importance for baking is the definition of sensitivity to antibiotics. Critical to the diagnosis of mycobacteriosis is the criterion of the simultaneous appearance of clinical, radiological, laboratory data and the isolation of a pure culture of non-tuberculosis mycobacteria, conducting multiple studies in dynamics.
An auxiliary value in diagnosis is the definition of antitheses with the help of RNGA, RP, immunoelectrophoresis, RNIF and ELISA, as well as the setting of skin allergic tests with sensitins.
Treatment and specific prevention of mycobacteriosis
All types of nontuberculous mycobacteria, with the exception of M. Xenopi, are resistant to isoniazil, streptomycin and thiosemicarbazone. Treatment of mycobacteriosis with anti-tuberculosis and antibacterial drugs should be long (12-13 months) and combined. Usually, it is ineffective with MAC-infectious disease and diseases caused by fast-growing mycobacteria. In some cases, surgical treatment is used. Preparations for specific prevention of mycobacteriosis have not been developed.