In vitro activity of fluoroquinolones, vancomycin, and gentamicin against methicillin-resistant Staphylococcus aureus ocular isolates

PURPOSE: To determine the antibacterial activity of fluoroquinolones, vancomycin, and gentamicin against methicillin,resistant Staphylococcus aureus (MRSA) ocular surface isolates. DESIGN: Retrospective review. METHODS: MRSA isolates were obtained from 21 patients. The MIC50 (mean inhibitory concentration) (mu g/ml) values of 31 MRSA ocular surface isolates were determined for gatifloxacin, moxifloxacin, ciprofloxacin, ofloxacin, vancomycin, and gentamicin using the Etest (AB Biodisk, Solna, Sweden) or the VITEK system (bioMerieux, Inc, Durham, North Carolina, USA). Susceptibility data were interpreted based on criteria specified by the Clinical and Laboratory Standards Institute (CLSI). MAIN OUTCOME MEASURES: MIC50 values in mu g/ml and interpretation of susceptibility or resistance. 0 RESULTS: In vitro resistance rates and median MIC50 in mu g/ml for the MRSA isolates were: gatifloxacin (71%, 8.0), moxifloxacin (68%, 8.0), ciprofloxacin (94%, 8.0), ofloxacin (94%, 8.0), vancomycin (0%, 1.0), and gentamicin 0%, 0.5). CONCLUSIONS: MRSA ocular isolates exhibited a relatively high rate of in vitro resistance to all fluoroquinolones tested, including the fourth generation. In contrast, MRSA isolates were found to be highly sensitive to vancomycin and gentamicin.