ASSOCIATION OF BORDERLINE OXACILLIN-SUSCEPTIBLE STRAINS OF STAPHYLOCOCCUS-AUREUS WITH SURGICAL-WOUND INFECTIONS

Staphylococcus aureus isolates which produce type A staphylococcal bet a-lactamase have been associated with wound infections complicating th e use of cefazolin prophylaxis in surgery. To further evaluate this fi nding, 215 wound isolates from 14 cities in the United States were cha racterized by antimicrobial susceptibility and beta-lactamase type and correlated with the preoperative prophylactic regimen. Borderline-sus ceptible S. aureas isolates of phage group 5 (BSSA-5), which produce l arge amounts of type A beta-lactamase and exhibit borderline susceptib ility to oxacillin, comprised a greater percentage of the 120 wound is olates associated with cefazolin prophylaxis than they did of the 95 i solates associated with other prophylactic regimens (25% versus 12.6%, respectively; P < 0.05). In contrast, methicillin-resistant S, aureus isolates were distributed evenly between the two groups (8.3% versus 11.6%, respectively). In vitro assays demonstrated that cefazolin was hydrolyzed faster by BSSA-5 strains than by other beta-lactamase-produ cing, methicillin-susceptible strains (1.54 versus 0.50 mu g/min/10(8) CFU, respectively; P < 0.0001). These data demonstrate that BSSA-5 st rains are a distinct subpopulation of methicillin-susceptible S, aureu s which frequently cause deep surgical wound infections. Cefazolin use in prophylaxis is a risk factor for BSSA-5 infection.