Prevalence and genotypic structure of mixed cultures of <i>Mycobacterium tuberculosis</i> among patients with HIV-associated tuberculosis in St. Petersburg

The aim of the study was to assess the frequency of mixed infections caused by several strains (mixed culture) of Mycobacterium tuberculosis among patients with HIV-associated generalized tuberculosis in St. Petersburg, and to conduct a comparative analysis of the genotypic diversity of strains in mixed cultures and among “pure” cultures of the tuberculosis pathogen. Materials and methods. A total of 173 M. tuberculosis isolates obtained from autopsy specimens of 70 patients with HIV-associated generalized tuberculosis between 2012 and 2018 were analyzed. The Beijing genotype and its subtypes were determined using PCR and IS6110-RFLP typing. Non-Beijing isolates were spoligotyped, and their genetic families were identified using the international SITVIT2 database. Genotypic resistance to rifampicin and isoniazid was detected using the Amplitub-MDR-RV test system. Results. Mixed infections were detected in 15 of 70 patients with HIV-associated multidrug-resistant tuberculosis. The same M. tuberculosis genotypes—Beijing, LAM, Ural, Haarlem, and X—were identified in the mixed cultures as in the pure cultures. Beijing strains, primarily subtypes B0/W148 (60%) and CAR (53.3%), were detected in all mixed cultures. The proportions of B0/W148 and LAM strains were significantly higher among mixed cultures (p 0.05). Strains from mixed cultures had more than one mutation in different codons in the rpoB gene. Mixed cultures were more common in patients serving sentences in penal institutions (p = 0.0007). Conclusions. The proportion of mixed infections among patients with HIV-associated tuberculosis was 21.4%; all mixed cultures contained strains of the Beijing genotype. A history of imprisonment was a significant risk factor for developing mixed infections.