| Approximately two million people succumb to tuberculosis (TB) each year. The emergence of multi-drug resistant (MDR) tuberculosis has further complicated treatment and control of the disease. MDR TB treatment requires use of second-line drugs such as capreomycin, kanamycin, amikacin and viomycin and cross-resistance among these is a concern during therapy. Mutations in the 16S rRNA gene ( rrs) have been associated with the cross-resistance; however, studies at the molecular level are limited and the results are variable. It is particularly concerning that relatively little is known about the mechanism of action or molecular basis of mono- or cross-resistance of capreomycin, an important second-line antibiotic.;The basis of capreomycin resistance was investigated by isolating and characterizing capreomycin-resistant strains of Mycobacterium smegmatis and Mycobacterium tuberculosis. Utilization of transposon-mutagenized M. smegmatis and M. tuberculosis identified the involvement of tlyA in capreomycin resistance. Disruption of tlyA was observed in spontaneous capreomycin-resistant mutants generated from M. smegmatis and M. tuberculosis wild type strains and in capreomycin-resistant clinical isolates. Complementation with wild-type tlyA restored susceptibility to capreomycin in M. smegmatis and M. tuberculosis tlyA mutants. Additionally, ribosomes from tlyA mutant but not tlyA+ strains resisted capreomycin inhibition of transcription-translation during in vitro studies. These data indicate that TlyA affects ribosomes and demonstrate that mutation of tlyA confers resistance to capreomycin in M. tuberculosis.;To investigate the molecular basis of cross-resistance among capreomycin, kanamycin, amikacin, and viomycin, M. tuberculosis laboratory-generated mutants and clinical isolates were examined. Three rrs mutations were found and each was associated with a particular cross-resistance pattern and drug minimal inhibitory concentration. Additionally, genotypic and phenotypic differences were seen among laboratory-generated mutants in the development of cross-resistance when M. tuberculosis bacteria were exposed to one versus two drugs.;Overall, this study identifies a tlyA involvement in capreomycin resistance. It additionally reveals an important role of 16S rRNA mutations in resistance to capreomycin as well as kanamycin, viomycin, and amikacin. The genotypic and phenotypic differences seen have implications for selection of drug treatment regimens. Finally, the data provide some insight into where and how these drugs may bind, which may be useful for future drug design studies. |
