Characterization of intrinsic efflux activity of Enterococcus faecalis ATCC29212 by a semi-automated ethidium bromide method

Gabriella Spengler, Ana Martins, Zsuzsanna Schelz, Liliana Rodrigues, Lone Aagaard, Marta Martins, Sofia Santos Costa, Isabel Couto, Miguel Viveiros, Séamus Fanning, Jette E. Kristiansen, Joseph Molnar, Leonard Amaral

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


Enterococcus faecalis is recognized as a multidrug-resistant nosocomial pathogen. The phenotypic basis for this is largely uncharacterized. The intrinsic efflux system of the antibiotic-susceptible E. faecalis ATCC29212 strain was studied using a semi-automated method that assesses accumulation and efflux of the universal efflux pump substrate ethidium bromide (EB). The results show that the intrinsic efflux system of this Enterococcus strain is controlled by energy derived from the catabolism of glucose and the proton concentration of the medium. At pH 5, agents that inhibit efflux pumps in Gram-positive organisms and the proton gradient un-coupler CCCP do not increase accumulation nor inhibit efflux of EB. In contrast, at pH 8, where the proton concentration is 1,000-fold lower, these agents increase accumulation and efflux of EB. These results are relevant to infections produced by E. faecalis and subsequent antibiotic therapy with antibiotics to which the organism is known to be intrinsically resistant.

Original languageEnglish
Pages (from-to)81-87
Number of pages7
JournalIn Vivo
Issue number1
Publication statusPublished - 1 Jan 2009


  • Carbonyl Cyanide m-Chlorophenyl Hydrazone
  • Cell Survival
  • Drug Resistance, Multiple, Bacterial
  • Enterococcus faecalis
  • Ethidium
  • Glucose
  • Membrane Transport Proteins
  • Microbial Sensitivity Tests
  • Reserpine
  • Thioridazine
  • Uncoupling Agents
  • Journal Article
  • Research Support, Non-U.S. Gov't


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