Mutation in the rpoB gene of the rifampicin resistant M. avium complex strains from Thailand.

Forms of mutation never before described in the rpoB gene are reported for a sample of 20 rifampicin-resistant Mycobacterium avium Complex (MAC) strains isolated from AIDS patients in Thailand. All strains were analyzed by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and polymerase chain reaction-DNA sequencing (PCR-DNA sequencing). Sequence analysis of these strains revealed that only one strain (5%) has missense mutation at Lys-626 (Thr) and the rest of the strains had 15 different silent mutations within a 542 bp region of the rpoB gene. Five strains (25%) had a silent mutation at only one position, 7 (35%) at 2 positions, 7 (35%) at 3 positions, and 1 (5%) at 7 positions. The silent mutation at the Ala-630 codon occurred in the largest proportion of the strains (15 strains, 75%), followed by the Val-581 in 8 strains (40%), Tyr-578 and Thr-600 in 4 strains (20%), and Gly-597 in 3 strains (15%). This investigation demonstrates that mutation in the rpoB gene of MAC strains from Thailand are more varied than previously reported for RIF MAC strains. PCR-SSCP screening clearly separated RIFr strains from rifampicin-susceptible (RIFs) strains.

Mutations in the rpoB gene of rifampicin-resistant Mycobacterium tuberculosis strains from Thailand and its evolutionary implication.

Novel mutations in the rpoB gene are reported for 70 rifampicin-resistant (RIFr) M. tuberculosis strains from Thailand. Sequence analysis of these strains revealed mutations in a 435 base-pair region of the rpoB gene. Twenty-eight strains (40%) had single mutations, and 26 of those strains had mutations at positions never before reported, of which, just one had a substitution at Val-432 (Asp), and the remaining 25, a silent mutation at Gln-517. All other strains had multiple mutations, of which 24 (34%) had mutations at two positions; 9(13%), at three positions; 2(3%), at five positions; and 1(1%) at six positions. Five strains (7%), reported to have the RIFr phenotype, contained no mutation in the examined region of the rpoB gene. Surprisingly, one RIFr strain had silent mutations at 29 positions. By far the dominant mutation was the silent mutations at Gln-517 (86%). This investigation demonstrates that mutations in the rpoB gene of M. tuberculosis strains from Thailand are more varied than previously reported for RIFr M. tuberculosis strains. Screening by means of PCR-SSCP clearly separated RIFr strains from rifampicin-susceptible (RIFs) strains. There was no correlation between RIFr mutations and random amplified polymorphic DNA (RAPD) types.