Nonstandard Evaluation of the Efficacy of Gel- and Liquid-Alcohol-Based Hand Rubs against Staphylococcus aureus by Chemical and Biological Electronic Scanning Microscopic Techniques

Abstract

Alcohol sanitisers are the most commonly used disinfectants and antiseptics in health care settings. Their efficacy is affected by concentration and contact time. The contact time can be studied with chemical kinetics that relates concentration, time and temperature in the Arrhenius equation based on kinetic molecular theory. The main objective of this paper was to present experimentally obtained results of the evaporation kinetics of liquid and gel alcohol based-hand rub sanitisers at 30 °C. The evaporation reaction of alcohol-based hand rubs follows a first order reaction and the rate constant is equal to 0.00066 and 0.001615 for gel and liquid sanitisers, respectively. The half-life of the gel and liquid rubs were 17.5 and 7.12 hr, respectively. The low value of the rate constant and high half life time of the gel-form sanitiser are related to it porous structure. The high half life time value caused by the effect of the porous structure expected to increase the contact time to inhibit the Staphylococcus aureus activity. In contrast, the electronic scanning microscope study of the gel and liquid biofilms of the alcohol based-hand rubs showed that cells grown in the liquid alcohol-based hand rub (AHR) medium exhibited more indentation and produced more cell debris than cells grown in the gel AHR. These configurations suggest that liquid AHRs are more effective at destroying Staphylococcus aureus cells than gel AHRs. Therefore, liquid AHRs are more efficient sanitisers than gel AHRs.