Activity of four antimicrobial cocktails for tissue allograft decontamination against bacteria and Candida spp. of known susceptibility at different temperatures
T. L. Pitt,
C. P. McDonald
National Bacteriology Laboratory, National Transfusion Microbiology Laboratory, National Health Service Blood and Transplant, Charcot Road, London, NW9 5BG, UK.
Several antimicrobial cocktail solutions of differing composition and concentrations are widely used to decontaminate viable banked tissue allografts at different temperatures and times of exposure. We compared the efficiency of four cocktails comprising nine antimicrobials to kill suspensions of a panel of 27 strains of 13 bacterial species, and 3 Candida spp. at 4, 22 and 37 °C for 24 h. All but one bacterial strains were susceptible to one or more of the agents tested individually at concentrations at least fourfold below the recommended susceptibility breakpoint minimum inhibitory concentrations for drug/species combinations. Candida lusitaniae was resistant to nystatin and amphotericin. The concentrations of several of the cocktail constituents were often greatly in excess (50–1,000-fold) of that required to inhibit the growth of susceptible strains. All cocktails were ineffective against a pan-resistant strain of Enterococcus faecium and one of the four cocktails failed to kill two strains of methicillin resistant Staphylococcus aureus. Each cocktail was most efficient at 37°C, less so at 22°C, and poorly active at 4°C. We conclude that the practice of decontamination of tissues with antimicrobials at low temperatures is not supported by in vitro susceptibility tests.