Second-line anti-tuberculosis drug resistance and its genetic determinants in multidrug-resistant Mycobacterium tuberculosis clinical isolates

Abstract Background Mutations in several genetic loci have been implicated in the development of resistance to second-line anti-tuberculosis (TB) drugs (SLDs). The purpose of this study was to investigate the prevalence of resistance to SLDs and its association with specific mutations in multidrug-resistant (MDR) Mycobacterium tuberculosis clinical isolates. Materials and methods The study included 46 MDR-TB isolates. Mutation profiling was performed by amplifying and sequencing the following six genes: gyrA / gyrB , rrs , tlyA , and ethA / ethR , in which mutations are implicated in resistance of tubercle bacilli to ofloxacin (OFX), amikacin (AMK), capreomycin, and ethionamide (ETH), respectively. Results Of the strains analyzed, 14 (30.4%) showed resistance to at least one of the four SLDs tested. Mutations in the gyrA gene occurred in 34 (73.9%) strains, with the most common amino acid change being Ser95Thr. The Asp94Asn and Ala90Val substitutions in the gyrA were present exclusively in OFX-resistant strains, yet represented only 40% of all OFX-resistant strains. The only mutation in the gyrB gene was substitution Ser447Phe, detected in one OFX-resistant isolate. None of the AMK-resistant strains carried a mutation in the rrs gene. Mutations in the ethA / ethR loci were found in one ETH-resistant and 11 ETH-susceptible strains. Conclusions The results of this study challenge the usefulness of sequence analyses of tested genes (except gyrA ) for the prediction of SLD resistance patterns and highlight the need for searching other genetic loci for detection of mutations conferring resistance to SLDs in M. tuberculosis .