Microbiological and genetic typing of atypical mycobacteria identified in the Novosibirsk region

Abstract

219 samples of biological material from animals and 54 samples of environmental objects from farms in the Novosibirsk region, which are free from bovine tuberculosis, were examined for isolation of the tuberculosis pathogen, microbiological and genetic typing of isolated cultures of atypical mycobacteria. Microbiologic diagnosis included culture method, biochemical tests and biological assay. During the treatment of animal biomaterial 50 cultures were isolated, and 20 cultures were isolated from the environmental objects. The isolated cultures were classified as mycobacteria on the basis of their culture and morphological properties and bacterioscopy. According to biochemical characteristics, out of 70 cultures studied, 27 isolates (38.6%) belonged to atypical mycobacteria of different species. Of these, 26 cultures (96.3%) were categorized as Group III and 1 culture (3.7%) as Group IV according to Runyon's classification. Next, a biological assay was performed by infecting nonlinear white mice with suspensions of 27 identified cultures of atypical mycobacteria. At autopsy and pathological-anatomical study of laboratory animals, changes in internal organs characteristic for tuberculosis were not found, which confirms that the cultures under study belong to atypical mycobacteria. Molecular systematization of the isolated cultures revealed the presence of Mycobacterium avium (20 cultures, 74%), M. nonchromogenicum (5 cultures, 18.5%), M. intracellulare (1 culture, 3.7%) and M. fortuitum (1 culture, 3.7%). Thus, based on the results of a comprehensive study of 70 cultures of atypical mycobacteria isolated from animal biomaterial and environmental objects from the territory of farms in the Novosibirsk region, free from bovine tuberculosis, 27 isolates belonging to atypical mycobacteria of groups III and IV were identified according to Runyon’s classification. On the basis of typing, it was found that the leading role among the identified pathogens is occupied by atypical mycobacteria of group III, in particular M. avium. The etiology of nonspecific tuberculin reactions in tuberculosis-free herds of cattle can be explained by the isolation of atypical Mycobacterium tuberculosis groups III and IV according to Runyon classification from environmental objects and their persistence in the organism of healthy animals.