JAC Advance Access published online on October 14, 2009
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkp369
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Original research |
The Enterococcus faecalis superoxide dismutase is essential for its tolerance to vancomycin and penicillin
Laboratoire de microbiologie de l'environnement, EA956, USC INRA 2017, Université de Caen, Caen, France
Received 31 August 2009; returned 16 September 2009; revised 18 September 2009; accepted 22 September 2009
* Corresponding author. Tel: +33-2-31-56-54-04; Fax: +33-2-31-56-53-11; E-mail: Axel.Hartke{at}unicaen.fr
Objectives: Enterococcus faecalis is a human commensal that has the ability to become a pathogen. Because of its ruggedness, it can persist in the hospital setting and cause serious nosocomial infections. E. faecalis can acquire multiple drug resistance determinants but is also intrinsically tolerant to a number of antibiotics, such as penicillin or vancomycin, meaning that these usually bactericidal drugs only exhibit a bacteriostatic effect. Recently, evidence has been presented that exposure to bactericidal antibiotics induced the production of reactive oxygen species in bacteria. Here, we studied the role of enzymes involved in the oxidative stress response in the survival of E. faecalis after antibiotic treatment.
Methods: Mutants defective in genes encoding oxidative stress defence activities were tested by time–kill curves for their contribution to antibiotic tolerance in comparison with the E. faecalis JH2-2 wild-type (WT).
Results: In killing assays, WT cultures lost 0.2 ± 0.1 and 1.3 ± 0.2 log10 cfu/mL after 24 h of vancomycin or penicillin exposure, respectively. A deletion mutant of the superoxide dismutase gene (
sodA) exhibited a lack of tolerance as cultures lost 4.1 ± 0.5 and 4.8 ± 0.7 log10 cfu/mL after 24 h of exposure to the same drugs. Complementation of sodA re-established the tolerant phenotype. Bacterial killing was an oxygen-dependent process and a model is presented implicating the superoxide anion as the mediator of this killing. As predicted from the model, a mutant defective in peroxidase activities excreted hydrogen peroxide at an elevated rate.
Conclusions: SodA is central to the intrinsic ability of E. faecalis to withstand drug-induced killing, and the superoxide anion seems to be the key effector of bacterial death.
Key Words: oxidative stress , bactericidal effect , reactive oxygen species
Present address: Institute of Microbiology, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland.