Characterization of RPO B gene for detection of rifampicin drug resistance by SSCP and sequence analysis

Because of the emergence of multidrug-resistant tuberculosis in recent times, the rapid detection of resistance to the first-line anti-tuberculosis drug rifampicin was felt worldwide. Accordingly, this study was conducted to evaluate the diagnostic potential of polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) for checking its utility as a rapid screening test for determination of rifampicin drug resistance.

A total of 34 isolates of Mycobacterium tuberculosis (M. tuberculosis) (22 rifampicin resistant, 11 rifampicin sensitive and one control H37Rv) strains were analysed by PCR-SSCP and DNA sequencing within the 157-bp region of the rpo B gene (Ala 500-Val 550).

Rifampicin resistance was detected successfully by PCR-SSCP in 20/22(90.90%) of rifampicin-resistant strains showing a total of nine different mutations in seven codon positions: codon 513 (CAA-->CCA), 516 (GAC-->GTC), 507 (GGC-->GAC), 526 (CAC-->GAC, TAC), 531 (TCG-->TTG, TGG), 522 (TCG-->TGG) and 533 (GTG-->CCG). Two rifampicin-resistant strains showed an identical PCR-SSCP pattern with the wild type H37Rv; 77.27% rifampicin-resistant strains showed a single point mutation and 9.09% had no mutation. Three rifampicin-resistant strains showed characteristic double mutations at codon positions 526 and 531. Sensitivity and specificity were calculated as 90.90% and 100%.

Rifampicin-resistant genotypes were mainly found in codon positions 516, 526 and 531. PCR-SSCP seems to be an efficacious method of predicting rifampicin resistance and substantially reduces the time required for susceptibility testing from 4 to 6 weeks to a few weeks.