The genetic diversity of Mycobacterium tuberculosis strains in thailand studied by amplification of DNA segments containing direct repetitive sequences

Abstract

OBJECTIVE: To develop and use a polymerase chain reaction (PCR) method for studying the genetic diversity of Mycobacterium tuberculosis. DESIGN: Two polymorphic DNA segments of M. tuberculosis H37Rv were identified and sequenced. Primers were then designed for simultaneous amplification of both polymorphic segments. The method was used for studying 179 clinical isolates of M. tuberculosis that had been previously characterized by Southern hybridization with IS6110. RESULTS: Both polymorphic segments contained direct repetitive sequences. In one segment the direct repetitive sequences were within the putative coding sequence of α-isopropylmalate synthase gene. After amplifying both segments of the 179 isolates, 40 patterns of PCR products could be identified. The method was able to differentiate 38 IS6110- single-banded isolates into 23 types. Most of the isolates belonging to the Beijing family had PCR products identical to the H37Rv strain. The PCR products of the members of the Nonthaburi group were similar to each other. CONCLUSION: These results agree with the hypothesis that the members of the Beijing family and the Nonthaburi group descended from two common ancestors. The PCR method might be useful for differentiating strains of M. tuberculosis that contain a single copy of IS6110.