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Open Access Highly Accessed Research article

Functional genomic analysis of bile salt resistance in Enterococcus faecium

Xinglin Zhang*, Damien Bierschenk, Janetta Top, Iacovos Anastasiou, Marc JM Bonten, Rob JL Willems and Willem van Schaik

Author Affiliations

Department of Medical Microbiology, University Medical Center Utrecht, Heidelberglaan 100; Room G04.527, Utrecht, 3584 CX, The Netherlands

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BMC Genomics 2013, 14:299  doi:10.1186/1471-2164-14-299

Published: 3 May 2013



Enterococcus faecium is a Gram-positive commensal bacterium of the mammalian intestinal tract. In the last two decades it has also emerged as a multi-resistant nosocomial pathogen. In order to survive in and colonize the human intestinal tract E. faecium must resist the deleterious actions of bile. The molecular mechanisms exploited by this bacterium to tolerate bile are as yet unexplored.


In this study we used a high-throughput quantitative screening approach of transposon mutant library, termed Microarray-based Transposon Mapping (M-TraM), to identify the genetic determinants required for resistance to bile salts in E. faecium E1162. The gene gltK, which is predicted to encode a glutamate/aspartate transport system permease protein, was identified by M-TraM to be involved in bile resistance. The role of GltK in bile salt resistance was confirmed by the subsequent observation that the deletion of gltK significantly sensitized E. faecium E1162 to bile salts. To further characterize the response of E. faecium E1162 to bile salts, we performed a transcriptome analysis to identify genes that are regulated by exposure to 0.02% bile salts. Exposure to bile salts resulted in major transcriptional rearrangements, predominantly in genes involved in carbohydrate, nucleotide and coenzyme transport and metabolism.


These findings add to a better understanding of the molecular mechanisms by which E. faecium responds and resists the antimicrobial action of bile salts.

Enterococcus faecium; Bile resistance; Transposon mutant library; Transcriptome