THE EPIDEMIOLOGY OF RESISTANCE TO OFLOXACIN AND OXACILLIN AMONG CLINICAL COAGULASE-NEGATIVE STAPHYLOCOCCAL ISOLATES - ANALYSIS OF RISK-FACTORS AND STRAIN TYPES

Coagulase-negative staphylococci are important nosocomial pathogens th at increasingly are resistant to oxacillin and fluoroquinolones. To de termine predictors of acquisition of oxacillin and ofloxacin resistanc e, we prospectively identified 150 patients from whose clinical specim ens coagulase-negative staphylococci were isolated that differed in su sceptibility to oxacillin and ofloxacin. In multivariate analysis, iso lation of ofloxacin-resistant coagulase-negative staphylococci was ass ociated with receipt of aminoglycosides (odds ratio [OR] = 8.45; 95% c onfidence interval [CI] = 2.10-34.1; P = .001) and fluoroquinolones (O R = 11.50; 95% CI = 4.15-31.6; P < .001) within 30 days; oxacillin res istance was associated with prior receipt of beta-lactam agents (OR = 5.99; 95% CI = 2.91-12.3; P < .001), Among oxacillin-resistant strains , there was heterogeneity of pulsed-field gel electrophoresis (PFGE) t ypes, and no type was common between ofloxacin-resistant and ofloxacin -susceptible strains. Thus ofloxacin resistance may have emerged de no vo among diverse oxacillin-resistant strains following the selection p ressures of antimicrobial therapy, In contrast, 50% of patients with o xacillin susceptible/ofloxacin-resistant strains had one of two PFGE t ypes, a finding suggesting that person-to-person transmission resulted in the dissemination of some of these strains.