Molecular snapshot of drug-resistant and drug-susceptible Mycobacterium tuberculosis strains circulating in Bulgaria.

We report results of the first study on the molecular basis of drug resistance in Mycobacterium tuberculosis strains currently circulating in Bulgaria. The study panel consisted of 133 (including 37 drug-resistant) isolates recovered from newly diagnosed, adult pulmonary TB patients from different regions of Bulgaria in 2005--2006. Three types of the rpoB mutations were found in 20 of 27 RIF-resistant isolates; rpoB S531L was the most frequent. Eleven (48%) of 23 INH-resistant isolates had katG S315T mutation. inhA -15C > T mutation was detected in one INH-resistant isolate (that also had katG315 mutation) and three INH-susceptible isolates. A mutation in embB306 was found in 7 of 11 EMB-resistant isolates. Comparison with spoligotyping and 24-VNTR locus typing data suggested that emergence and spread of drug-resistant and MDR-TB in Bulgaria are not associated with any specific spoligotype or MIRU-VNTR genotype.