Geographical profile of rpoB gene mutations in rifampicin resistant Mycobacterium tuberculosis isolates in Sri Lanka.

The nature and frequency of mutations in the rpoB gene of rifampicin (RIF) resistant Mycobacterium tuberculosis clinical isolates varies considerably between different geographical regions. The objective of the present study was the identification of rpoB gene mutations responsible for RIF resistance in M. tuberculosis isolates in Sri Lanka. Three regions of the rpoB gene of M. tuberculosis, one corresponding to a 437-bp region, including the rifampicin resistance-determining region (RRDR) and two other regions (1395 bp and 872 bp) spanning the RRDR, were polymerase chain reaction amplified, and were subjected to DNA sequencing. The two mutations found within the RRDR in the 31 RIF resistant strains isolated in this study were at codon 526 (n=15, 48.4%) CAC (His)→TAC (Tyr) and codon 531 (n=3, 9.7%) TCG (Ser)→TTG (Leu). A significant proportion (n=15, 48.3%) showed mutations spanning the RRDR, including two novel mutations at codon 626 (n=13, 41.9%) GAC (Asp)→GAG (Glu) and 184 (n=2, 6.4%) GAC (Asp)→GAT (Asp), a silent mutation. Two isolates revealed double mutations (codons 626+526 and 626+184). The presence of a high frequency of new mutations, and the different frequencies of the universally prevailing mutations, as reported here, emphasizes the need for expanding the geographical database of mutations for effective application of an rpoB-based diagnosis of multidrug resistant tuberculosis.