Loss of vancomycin bactericidal activity against accessory gene regulator (agr) dysfunctional Staphylococcus aureus under conditions of high bacterial density

The impact of accessory gene regulator (agr) dysfunction and high bacterial density on vancomycin killing and resistance was evaluated among 10 clinical methicillin-resistant Staphylococcus aureus bloodstream isolates using time kill experiments. Under conditions of high inocula and agr dysfunction, vancomycin activity was markedly attenuated, amplifying resistant mutants by 72 h.