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Journal of Bacteriology, November 2008, p. 7357-7366, Vol. 190, No. 22
0021-9193/08/$08.00+0 doi:10.1128/JB.00485-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Department of Molecular Microbiology,1 Department of Molecular Genetics, Groningen Biomolecular Sciences and Biotechnology Institute and the Kluyver Centre for Genomics of Industrial Microorganisms, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands2
Received 9 April 2008/ Accepted 2 September 2008
Upon prolonged exposure to cholate and other toxic compounds, Lactococcus lactis develops a multidrug resistance phenotype that has been attributed to an elevated expression of the heterodimeric ABC-type multidrug transporter LmrCD. To investigate the molecular basis of bile acid resistance in L. lactis and to evaluate the contribution of efflux-based mechanisms in this process, the drug-sensitive L. lactis NZ9000
lmrCD strain was challenged with cholate. A resistant strain was obtained that, compared to the parental strain, showed (i) significantly improved resistance toward several bile acids but not to drugs, (ii) morphological changes, and (iii) an altered susceptibility to antimicrobial peptides. Transcriptome and transport analyses suggest that the acquired resistance is unrelated to elevated transport activity but, instead, results from a multitude of stress responses, changes to the cell envelope, and metabolic changes. In contrast, wild-type cells induce the expression of lmrCD upon exposure to cholate, whereupon the cholate is actively extruded from the cells. Together, these data suggest a central role for an efflux-based mechanism in bile acid resistance and implicate LmrCD as the main system responsible in L. lactis.
Published ahead of print on 12 September 2008.
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