THE GENETIC DIVERSITY OF MYCOBACTERIUM-TUBERCULOSIS STRAINS IN THAILAND STUDIED BY AMPLIFICATION OF DNA SEGMENTS CONTAINING DIRECT REPETITIVE SEQUENCES

OBJECTIVE: To develop and use a polymerase chain reaction (PCR) method for studying the genetic diversity of Mycobacterium tuberculosis. DES IGN: Two polymorphic DNA segments of M. tuberculosis H37Rv were identi fied and sequenced. Primers were then designed for simultaneous amplif ication of both polymorphic segments. The method was used for studying 179 clinical isolates of M. tuberculosis that had been previously cha racterized by Southern hybridization with IS6110. RESULTS: Both polymo rphic segments contained direct repetitive sequences. In one segment t he direct repetitive sequences were within the putative coding sequenc e of alpha-isopropylmalate synthase gene. After amplifying both segmen ts of the 179 isolates, 40 patterns of PCR products could be identifie d. The method was able to differentiate 38 IS6110-single-banded isolat es into 23 types. Most of the isolates belonging to the Beijing family had PCR products identical to the H37Rv strain. The PCR products of t he members of the Nonthaburi group were similar to each other. CONCLUS ION: These results agree with the hypothesis that the members of the B eijing family and the Nonthaburi group descended from two common ances tors. The PCR method might be useful for differentiating strains of M. tuberculosis that contain a single copy of IS6110.