Three novel highly charged copper-based biocides: safety and efficacy against healthcare-associated organisms

Abstract

We investigated three novel highly charged copper-based inorganic biocidal formulations for their activity against organisms highly relevant to healthcare-associated infection. The three copper-based formulations were tested: (i) against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), Legionella pneumophila, Acinetobacter calcoaceticus/baumannii (ACCB), glycopeptide-resistant Enterococcus and spores of Clostridium difficile in time-kill assays; (ii) for their ability to decontaminate ultramicrofibre (UMF) cloths; and (iii) for their cytotoxicity to human skin and intestinal epithelial cells. All three copper-based formulations were potently biocidal down to concentrations of 1 ppm for both stationary- and log-phase organisms, and they were all active against C. difficile spores. At 150 ppm, they achieved a complete (>6 log10) kill of MRSA and ACCB mostly within 1 h. This biocidal activity was not achieved by copper sulphate or the inorganic binders used in the formulations. All three copper-based formulations completely decontaminated UMF cloths containing MRSA, ACCB or C. difficile spores, suggesting that any of these copper-based formulations would be highly beneficial in the healthcare environment. All three copper-based formulations and copper sulphate were not cytotoxic to human epithelial cells up to concentrations of 100-200 ppm. All three of the novel copper-based biocidal formulations, but not their components (copper sulphate and inorganic binders), have potent activity against organisms highly relevant to healthcare-associated infections.