JAC Advance Access originally published online on September 26, 2008
Journal of Antimicrobial Chemotherapy 2008 62(6):1273-1276; doi:10.1093/jac/dkn407
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Original research |
SmvA, and not AcrB, is the major efflux pump for acriflavine and related compounds in Salmonella enterica serovar Typhimurium
1 Laboratorio de Microbiología, Departamento de Ciencias Biológicas, Universidad Andrés Bello, Santiago, Chile 2 Programa de Microbiología y Micología, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
Received 1 August 2008; returned 19 August 2008; revised 2 September 2008; accepted 3 September 2008
* Corresponding author. Tel: +56-2-661-8374; Fax: +56-2-661-8069; E-mail: gmora{at}unab.cl
Objectives: The aim was to study the role played by SmvA pump in the efflux of quaternary ammonium compounds (QACs) in Salmonella enterica serovar Typhimurium (Salmonella Typhimurium).
Methods: Mutants in the smvA, acrB and tolC genes were constructed by the red swap method. P22 was used to transduce tolC to acrB and smvA mutant strains. The susceptibility of these strains to acriflavine and a variety of QACs was determined by MIC assays.
Results: In comparison with the Salmonella Typhimurium wild-type strain, the smvA mutant was more susceptible to QACs than the acrB mutant strain. A tolC single mutant was more susceptible than an acrB mutant to QACs, acriflavine, ethidium bromide, malachite green and pyronin B. The tolC–acrB double mutant was as susceptible as the single tolC mutant to QACs. Additionally, the smvA mutant strain was more susceptible to acriflavine than the acrB mutant (MICs = 31.3 versus 125 mg/L, i.e. 4-fold). Finally, the tolC–smvA double mutant (3.9 mg/L) was approximately 10 times more susceptible to acriflavine than either smvA (31.3 mg/L) or tolC (31.3 mg/L) single mutants.
Conclusions: It is the SmvA efflux pump, and not AcrB, that plays the major role in the efflux of acriflavine and other QACs from Salmonella Typhimurium. This apparently conflicting report is due to the fact that in Escherichia coli the smvA gene does not exist. Our results suggest that tolC and smvA genes encode components of two different efflux systems with overlapping specificities that work in parallel to export acriflavine and other QACs.
Keywords: multidrug resistance , quaternary ammonium compounds , TolC , enteric bacteria
Present address. Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY, USA.