This paper reports investigations on the mode of action of AHR on Staphylococcus aureus. The results suggest that a better understanding of the survival mechanisms of the less susceptible isolates is important to identify, to ensure that AHR formulations achieve lethality against all bacterial isolates. In terms of mechanisms of action, the bactericidal efficacy of AHR is more likely to be the result of denaturation of bacterial cell proteins leading to loss of structural integrity and disruption of cellular function. Journal of Hospital Infection. 2010;76;264–79