evaluation of sensitivity of molecular methods for detection of rifampin-resistant strains amongst drug-resistant mycobacterium tuberculosis isolates

Background: resistance to rifampin in multidrug-resistant m. tuberculosis (mdr-tb) is one of the major threats to the global public health system. objectives: the aim of the present study was to explore the molecular characterization of resistance against rifampin amongst multidrug-resistant (mdr) and extensively drug-resistant (xdr) isolates obtained from patients. methods: in this study, we used xdr (n = 6), mdr (n = 9) and rifampin sensitive (n = 39) isolates whose drug susceptibility patterns were identified by proportion method. a simple single-step multiplex-allele specific-polymerase chain reaction (mas-pcr) assay was optimized to detect the three most frequent mutations in rifampin resistance-determining region (rrdr) fragment of rpob gene. additionally, single-strand conformational polymorphism (sscp)-pcr and sequencing were utilized. results: out of nine mdr isolates, five were detected by mas-pcr as rifampin resistant (sensitivity; 55.5%). in comparison with the proportion method, the sensitivity of sscp for xdr, mdr and rifampin sensitive isolates were 83.3%, 77.7% and 97.4%, respectively. the dna sequencing revealed that three of the 6 xdr isolates had several silent mutations, one isolate had one silent mutation, one strain had no mutations and only one isolate had mutations at codon 531. conclusions: in sum, although the molecular methods are rapid, they are not able to identify resistance against rifampin efficiently.