Overexpression of Stenotrophomonas maltophilia major facilitator superfamily protein MfsA increases resistance to fluoroquinolone antibiotics.

Abstract

Stenotrophomonas maltophilia is an opportunistic human pathogen causing nosocomial infections worldwide. S. maltophilia infection is of particular concern due to its inherent resistance to currently used antibiotics. Proton motive force-driven transporters of the major facilitator superfamily frequently contribute to the efflux of substances, including antibiotics, across cell membranes. An mfsA expression plasmid (pMfsA) was constructed and transferred into bacterial strains by electroporation. The antibiotic susceptibility levels of S. maltophilia strains were determined using standard methods. S. maltophilia MfsA is an efflux pump associated with paraquat resistance. We show here that plasmid-mediated overexpression of mfsA in WT S. maltophilia K279a increased resistance not only to paraquat but also to second-generation fluoroquinolone antibiotics, i.e. ciprofloxacin, norfloxacin, levofloxacin and ofloxacin. Ciprofloxacin was used as a representative drug. Addition of the proton motive force inhibitor carbonyl cyanide-m-chlorophenylhydrazone increases susceptibility to ciprofloxacin. Taken together these results suggest that MsfA is a novel fluoroquinolone efflux pump of S. maltophilia. Moreover, heterologous expression of mfsA in other Gram-negative pathogenic bacteria conferred resistance to paraquat as well as to fluoroquinolones. Thus, if this determinant was horizontally transferred, it could cause the spread of fluoroquinolone resistance among bacterial species.