State Research Center for Applied Microbiology, Russian Research Institute of Phthisiopulmonology (Ministry of Health, Moscow).
To analyze drug-resistant clinical isolates of Mycobacterium tuberculosis obtained from patients referred to the institute from different parts of Russia, and to study the mechanisms of their rifampicin resistance.
Fifty clinical isolates of M. tuberculosis were analysed. Polymerase chain reaction (PCR) and sequencing were used to study the mechanisms of rifampicin resistance in 25 isolates.
Among cultures isolated from 50 patients, drug resistance was detected in 33. Most of the isolates were resistant to rifampicin (25 isolates), isoniazid (14 isolates), and streptomycin (seven isolates). Only 6% of the isolates were resistant to one drug, while 14% were resistant to two, 32% to three, 40% to four, and 8% to five drugs. Susceptible isolates were derived from 17 patients. The following point mutations and deletions in the rpoB locus, responsible for high level rifampicin resistance (more than 50 microg/ml in egg-based medium), were detected: G-->A/395 (Arg-->Gln), C-->T/232 (His-->Tyr), C-->T/221 (Ser-->Leu), G-->T/202 (Asp-->Tyr), GA-->TT/202-203 (Asp-->Phe), deltaATGGACCAG/199-207 (Met, Asp, Gin), A-->T/91 (Met-->Leu), TG-->CC/227-228 (Leu-->Ser), GAG-->AGT/349-350-351 (Gln-->Ser), deltaGGG/354(Gly).
A number of previously unrecognised genetic modifications in the rpoB region were found in rifampicin-resistant strains isolated from patients from different parts of Russia.