Microbiology: Oxacillin-Resistant Phenotypes of Staphylococcus aureus

Infections caused by oxacillin-resistant Staphylococcus aureus are a growing problem in the United States, accounting for considerable morbidity, mortality, and expense. The increasing incidence of these infections has led to frequent empiric use of broader spectrum antibiotics to treat these more resistant pathogens, contributing to further worsening of the resistance among gram-positive organisms. Three main mechanisms of oxacillin resistance in S aureus are described: (1) classic resistance, (2) modified S aureus phenotype, and (3) hyper-^-lactamase production. Correctly identifying the mechanism of resistance in S aureus isolates should lead to substantial changes in antibiotic use and in infection control protocols. These modifications in clinical practices could lead to cost savings, as well as a decreased potential for further antibiotic resistance.