Contribution of the multidrug efflux pump LfrA to innate mycobacterial drug resistance

Multidrug resistance (MDR) in bacteria has been associated with efflux pump s that export structurally unrelated compounds and decrease cytoplasmic dru g accumulation. To investigate MDR in mycobacteria, we studied the Mycobact erium smegmatis mutant mc(2)11, which is resistant to doxorubicin, tetracyc line, rhodamine, ethidium bromide and the hydrophilic fluoroquinolones. A g enomic library constructed from this mutant was used to select clones confe rring resistance to doxorubicin. Surprisingly, the clone selected encodes t he efflux pump LfrA, which has been reported to confer resistance to hydrop hilic fluoroquinolones, ethidium bromide, rhodamine, and acriflavine. To de fine the contribution of LfrA to the innate mycobacterial drug resistance a nd to the MDR phenotype in mc(2)11, the lfrA gene was disrupted in both the mc(2)11 mutant and the mc(2)155 wild-type parent. LfrA disruption of the w ild-type strain decreased resistance to ethidium bromide and acriflavine, a nd increased accumulation of ethidium bromide. However, disruption of lfrA gene results only in a 2-fold decrease in minimal inhibitory concentrations (MICs) for ciprofloxacin, doxorubicin, rhodamine, and accumulation of [C-1 4]ciprofloxacin was unchanged. LfrA disruption of the MDR strain mc(2)11 pr oduced a similar phenotype. Thus, LfrA contributes significantly to the int rinsic MICs of M. smegmatis for ethidium bromide and acriflavine, but not f or ciprofloxacin, doxorubicin or rhodamine. (C) 2000 Federation of European Microbiological Societies. Published-by Elsevier Science: B.V. All rights reserved.