First report of mefA and msrA/msrB multidrug efflux pumps associated with blaTEM-1 β-lactamase in Enterococcus faecalis

Objectives: Enterococcus faecalis is thought to possess a great deal of intrinsic resistance to several antimicrobial agents. In this study we identified ampicillin-and erythromycin-resistant clinical isolates of E. faecalis and sought to identify the resistance mechanisms among these isolates. Methods: Twelve isolates of E. faecalis were collected from 12 different patients. Identification of the isolates and their susceptibility patterns were determined using the Phoenix automated phenotypic identification criteria. PCR amplification and sequencing were used to detect beta-lactamase production. Colony blotting was performed in order to screen for multidrug efflux pump production. Extraction and N-terminal sequencing of the multidrug efflux pumps was carried out. Results: The E. faecalis isolates showed high resistance to erythromycin and ampicillin, with minimum inhibitory concentrations of >16 mu g/ml. PCR amplification and sequencing showed that isolates produced TEM-1 beta-lactamase. Colony blotting showed that these isolates harbored multidrug efflux pump genes. Multidrug efflux pump extraction, purification, and sequencing showed the distribution of mefA and msrA/msrB efflux pumps. Conclusion: Two resistance mechanisms among E. faecalis are described - the production of TEM beta-lactamase and mefA and msrA/msrB efflux pumps. These results are of great interest because this is the first report of the co-existence of these resistance mechanisms among E. faecalis strains. (C) 2011 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.