Detection of rifampicin resistance of Mycobacterium tuberculosis using multiplex allele specific polymerase chain reaction (MAS-PCR) in Pakistan.

Drug resistance in tuberculosis (TB) is a major public health challenge in developing countries such as Pakistan. Multiplex allele specific polymerase chain reaction (MAS-PCR) is a DNA amplification method that could contribute to rapid detection and control of drug resistant tuberculosis (DR-TB) in Pakistan. The purpose of this study was to test the utility of MAS-PCR to detect resistance in Pakistan. Drug susceptibility testing (DST) was used to identify rifampicin resistant and susceptible clinical isolates from TB cases in Pakistan. MAS-PCR was used to detect the most frequent mutations in the gene rpoB among 213 resistant and 37 susceptible isolates. Among 213 clinical isolates, MAS-PCR identified mutation D435Y (Asp435Tyr) in 24 (11.3%) cases, H445Y (His445Tyr) in 14 (6.6%), S450L (Ser450Leu) in 124 (58.2%) and S450W (Ser450Trp) in 18 (8.4%) cases. MAS-PCR did not detect known mutations in 33 (15.5%) cases. Among 12 cases, a novel mutation at codon 434 (Met434Ile) and a common variant at codon 435 (Asp435Tyr) was detected in rpoB gene which is indicative of double mutation. In 4 isolates, a novel mutation at codon 432 (Gln432Pro) was identified. In an additional 4 isolates, mutations Met434Val and His445Asn were identified. Moreover, a mutation in rpoB (Leu452Pro) was found in 5 isolates. DNA sequencing confirmed the absence of mutations in rpoB in the 8 remaining isolates. MAS-PCR had 88.3% sensitivity and 100% specificity using DST as the reference, which suggested that this method could be implemented as an initial marker for screening of multi-drug resistant tuberculosis (MDR-TB) in Pakistan.