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)(μg/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 (bioMérieux, 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 μg/ml and interpretation of susceptibility or resistance.

Results

In vitro resistance rates and median MIC₅₀ in μg/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 (3%, 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.