Int. J. Mol. Sci. 2012, 13(4), 4101-4123; doi:10.3390/ijms13044101
Article

Subminimal Inhibitory Concentrations of the Disinfectant Benzalkonium Chloride Select for a Tolerant Subpopulation of Escherichia coli with Inheritable Characteristics

Received: 1 December 2011; in revised form: 20 January 2012 / Accepted: 19 March 2012 / Published: 28 March 2012
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: Exposure of Escherichia coli to a subminimal inhibitory concentration (25% below MIC) of benzalkonium chloride (BC), an antimicrobial membrane-active agent commonly used in medical and food-processing environments, resulted in cell death and changes in cell morphology (filamentation). A small subpopulation (1–5% of the initial population) survived and regained similar morphology and growth rate as non-exposed cells. This subpopulation maintained tolerance to BC after serial transfers in medium without BC. To withstand BC during regrowth the cells up regulated a drug efflux associated gene (the acrB gene, member of the AcrAB-TolC efflux system) and changed expression of outer membrane porin genes (ompFW) and several genes involved in protecting the cell from the osmotic- and oxidative stress. Cells pre-exposed to osmotic- and oxidative stress (sodium chloride, salicylic acid and methyl viologen) showed higher tolerance to BC. A control and two selected isolates showing increased BC-tolerance after regrowth in BC was genome sequenced. No common point mutations were found in the BC- isolates but one point mutation in gene rpsA (Ribosomal protein S1) was observed in one of the isolates. The observed tolerance can therefore not solely be explained by the observed point mutation. The results indicate that there are several different mechanisms responsible for the regrowth of a tolerant subpopulation in BC, both BC-specific and general stress responses, and that sub-MIC of BC may select for phenotypic variants in a sensitive E. coli culture.
Keywords: Escherichia coli; quaternary ammonium compounds; benzalkonium chloride; selection of subpopulation; efflux pump; osmotic and oxidative stress response
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MDPI and ACS Style

Moen, B.; Rudi, K.; Bore, E.; Langsrud, S. Subminimal Inhibitory Concentrations of the Disinfectant Benzalkonium Chloride Select for a Tolerant Subpopulation of Escherichia coli with Inheritable Characteristics. Int. J. Mol. Sci. 2012, 13, 4101-4123.

AMA Style

Moen B, Rudi K, Bore E, Langsrud S. Subminimal Inhibitory Concentrations of the Disinfectant Benzalkonium Chloride Select for a Tolerant Subpopulation of Escherichia coli with Inheritable Characteristics. International Journal of Molecular Sciences. 2012; 13(4):4101-4123.

Chicago/Turabian Style

Moen, Birgitte; Rudi, Knut; Bore, Erlend; Langsrud, Solveig. 2012. "Subminimal Inhibitory Concentrations of the Disinfectant Benzalkonium Chloride Select for a Tolerant Subpopulation of Escherichia coli with Inheritable Characteristics." Int. J. Mol. Sci. 13, no. 4: 4101-4123.

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