What are the implications of increasing rates of oxacillin-resistant S aureus or MRSA isolates in both hospital and community settings?
Increasing rates of oxacillin-resistant S aureus or MRSA isolates in both hospital and community settings has complicated the treatment of S aureus IE. An increasing body of evidence suggests an association between high (but still susceptible on the basis of the Clinical and Laboratory Standards Institute definition) vancomycin MICs in S aureus and worse clinical outcome in both MRSA infections treated with vancomycin and MRSA bacteremia treated with antistaphylococcal penicillins. Importantly, this association between higher vancomycin MICs in infecting MSSA and worse clinical outcomes among patients treated with antistaphylococcal penicillins (not vancomycin) was externally validated in a large cohort of patients with MSSA IE. These data suggest that host- or pathogen-specific factors, rather than higher MICs of the infecting pathogen to vancomycin, contribute to the poor outcomes in these patients.