[Evaluation of reasons of the MDR M. tuberculosis strains dissemination by analysis of the rifampicin and/or isoniazid resistant isolates].

During the last years in Novosibirsk region of Russia the rate of TB patients infected by MDR strains of M. tuberculosis has been constantly increasing. This increase may occur as a result of the spontaneously mutated mycobacterium selection during treatment of patients or as a result of primary infection by the resistant M. tuberculosis, or also, as a result of both reasons in combination. If the main reason of MDR strain dissemination is selection of resistant bacterium during patient treatment, the equal apportionment of the dominated mutation into the mycobacterium genotypes would be observed. If the main reason is the primary infection by resistant M. tuberculosis, the unequal apportionment would be revealed. For deeper understanding of the main reasons of the fast MDR strains spreading in the region, the distribution of the main mutations over genotypes of strains in Novosibirsk (170 isolates) and Tomsk prison (51 isolates) was investigated. Mutations in rpoB gene associated with the rifampicin resistance and in katG (isoniazid resistance) were detected by biochips. M. tuberculosis genotypings were carried out by IS6110 PCR typing or MIRU typing, in the last method the twelve loci (MIRU 2, 4, 10, 16, 20, 23, 24, 26, 27, 31, 39, 40) have been used. The most frequent mutation in the rpoB gene was Ser531-->Leu (60-70% of the rifampicin resistant strains) and Ser315-->Thr in gene katG (80% of the isoniazid resistant M. tuberculosis). Both in Novosibirsk and in Tomsk prison the rates of clustered cases transmissions were high (69 and 63% respectively). Analysis of the distribution of the dominated mutations Ser531-->Leu (rpoB) and Ser315-->Thr (katG) revealed that all of them were detected in each clusters, but in Novosibirsk there were only two clusters, in which the percentage of strains, containing mutation Ser531-->Leu (rpoB) were higher (85.7% and 77.7% respectively, P < 0.05), then in others. Among the Tomsk prison's clusters it was revealed one in which the proportion of the Ser3 15-->Thr mutation in katGwas higher (96.4%, P < 0.05). The nonuniform distribution of the dominated mutations highlighted that the epidemic spread of drug-resistant strains of M. tuberculosis in region resulted from the selection of them during patient treatment and the subsequent transmission by TB patients.