Warnes, S.L. and Keevil, C.W.
Mechanism of copper surface toxicity in vancomycin-resistant enterococci following wet or dry surface contact
Applied and Environmental Microbiology, 77, (17), . (doi:10.1128/AEM.00597-11). (PMID:21742916).
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Contaminated touch surfaces have been implicated in the spread of hospital-acquired infections and the use of biocidal surfaces could help to reduce this cross contamination. In a previous study we reported the death of aqueous inocula of pathogenic Enterococcus faecalis or Enterococcus faecium isolates, simulating fomite surface contamination, in 1 hour on copper alloys compared to survival for months on stainless steel. In our current study we observed an even faster kill of over 6-log reduction of viable enterococci in less than 10 minutes on copper alloys with a ‘dry’ inoculum equivalent to touch contamination. We investigated the effect of copper (I) and (II) chelation and quenching reactive oxygen species on cell viability assessed by culture and their effect on genomic DNA, membrane potential and respiration in situ on metal surfaces. We propose that copper surface toxicity in enterococci involves direct or indirect action of released copper ionic species and generation of superoxide resulting in arrested respiration and DNA breakdown as the first stages of cell death. Fenton reaction generation of hydroxyl radicals does not appear to be the dominant instrument of DNA damage. The bacterial membrane potential is unaffected in the early stages of ‘wet’ and ‘dry’ surface contact suggesting that the membrane is not compromised until post cell death. These results also highlight the importance of correct surface cleaning protocols to perpetuate copper ion release and prevent chelation of ions by contaminants which could reduce surface efficacy
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