Delayed antimicrobial effects of skin disinfection by alcohol

Abstract

SUMMARY: Aqueous suspensions of Staphylococcus aureus were deposited on a Millipore filter and then exposed for a few seconds to 70 % ethyl alcohol. Viable counts of bacteria extracted from the filter immediately after exposure to alcohol, and, in replicate experiments, after a further period of 3 h, showed that the mean immediate reduction of 97·6 % in viable counts after treatment with alcohol was followed by a further mean reduction of 67· 1 % in the further 3 h holding time; the same bacterial suspensions allowed to dry on Millipore filters without exposure to alcohol showed a significantly smaller mean reduction in viable counts (34·3 %) during a further 3 h holding time. These findings support the view that the reported further fall in numbers of bacteria on hands while wearing gloves for 3 h after alcohol disinfection can be explained by sublethal damage to some of the bacteria, from which they can recover only if promptly inoculated on culture medium.