Responses of tolerant and nontolerant Staphylococcus aureus strains to methicillin treatment in an experimental infection in mice.

Staphylococcus aureus strains can be divided into tolerant and nontolerant strains on the basis of their survival in vitro in the presence of high concentrations of methicillin (greater than or equal to 64 micrograms/ml). A strain is defined as tolerant if more than 2% of the inoculum survives under these conditions. The response of five susceptible and five tolerant S. aureus strains to treatment with methicillin was studied in an experimental thigh infection in mice. Animals were treated with one and two injections of methicillin (2.5 mg per mouse). At the end of treatment, the number of CFUs in the thigh muscles infected with the susceptible strains was found to be significantly lower than that in the thigh muscles infected with the tolerant