Evidence that phosphate specific transporter is amplified in a fluoroquinolone resistant Mycobacterium smegmatis

We reported in an earlier study that active efflux of drug has a predominan t role in conferring resistance in a laboratory-generated ciprofloxacin-res istant mutant of Mycobacterium smegmatis. This mutant exhibited mRNA level overexpression, as well as chromosomal amplification, of the gene pstB, enc oding the putative ATPase subunit of phosphate specific transport (Pst) sys tem. We demonstrate here that this mutant shows enhanced phosphate uptake a nd that inactivation of pstB in the parental strain results in loss of high affinity phosphate uptake and hypersensitivity to fluoroquinolones. These findings suggest a novel role of the Pst system in active efflux, in additi on to its involvement in phosphate transport.