Intrinsic Resistance of Mycobacterium smegmatis to Fluoroquinolones May Be Influenced by New Pentapeptide Protein MfpA

Abstract

ABSTRACT The fluoroquinolones (FQ) are used in the treatment of Mycobacterium tuberculosis , but the development of resistance could limit their effectiveness. FQ resistance (FQ R ) is a multistep process involving alterations in the type II topoisomerases and perhaps in the regulation of efflux pumps, but several of the steps remain unidentified. Recombinant plasmid pGADIV was selected from a genomic library of wild-type (WT), FQ-sensitive M. smegmatis by its ability to confer low-level resistance to sparfloxacin (SPX). In WT M . smegmatis , pGADIV increased the MICs of ciprofloxacin (CIP) by fourfold and of SPX by eightfold, and in M . bovis BCG it increased the MICs of both CIP and SPX by fourfold. It had no effect on the accumulation of 14 C-labeled CIP or SPX. The open reading frame responsible for the increase in FQ R , mfpA , encodes a putative protein belonging to the family of pentapeptides, in which almost every fifth amino acid is either leucine or phenylalanine. Very similar proteins are also present in M . tuberculosis and M . avium . The MICs of CIP and SPX were lower for an M . smegmatis mutant strain lacking an intact mfpA gene than for the WT strain, suggesting that, by some unknown mechanism, the gene product plays a role in determining the innate level of FQ R in M . smegmatis .