Characterization of rifampicin-resistant Mycobacterium tuberculosis in Taiwan

Sixty-three rifampicin-resistant (Rif(r)) isolates of Mycobacterium tuberculosis from Kaohsiung, Taiwan, were analysed for mutations in the core region (69 bp, codons 511-533) of the rpoB gene. Some 84.1 % (53/63) of the resistant isolates showed mutations in this region, especially in codons 531 (41.5 %), 526 (18.9 %), 516 (15.1 %) and 533 (7.5 %). Five novel alleles of a total of 16 different types of mutations were identified in Rif(r) isolates. Ten Rif(r) isolates (15.9 %) exhibited no mutations in the core region of rpoB. Also, they did not show mutations in another 365 bp fragment (codons 99-220) of rpoB. The agar proportion method was used to determine the relationship between the degree of rifampicin resistance and alterations in the core region of rpoB. The results revealed that the mean MIC was 92.38 micro g ml(-1) for the 53 isolates with a mutation in the core region, whereas the mean MIC of the other 10 isolates without mutations was only 24.8 micro g ml(-1). This indicates that the isolates with mutations in the core region had higher levels of resistance than those without mutations in this region. IS6110 restriction fragment length polymorphism (RFLP) was used for typing of 55 Rif(r) M. tuberculosis isolates. Isolates contained two to 19 copies of IS6110, with sizes ranging from 600 to 16 000 bp. The majority (85 %) contained six to 16 copies. No strains lacking IS6110 were found. A total of 54 of 55 RFLP types were defined at the 90 % similarity level. The observation of varied IS6110-associated banding patterns indicates that an outbreak of drug-resistant tuberculosis did not occur in this area.