Ex vivo efficacy of gemifloxacin in experimental keratitis induced by methicillin-resistant Staphylococcus aureus

In recent years, the emergence of methicillin-resistant Staphylococcus aureus (MRSA) strains has been observed in ocular infections. Resistance of MRSA to second- and third-generation fluoroquinolones has increased interest in the fourth-generation fluoroquinolones. In this study, the antibacterial activity of gemifloxacin against MRSA ocular isolates in vitro and in a modified ex vivo rabbit keratitis model was investigated. In vitro susceptibility test results indicated that the minimum inhibitory concentrations (MICs) of gemifloxacin were lower than the MICs of other fluoroquinolones, including moxifloxacin (MIC50 range, 0.016-0.032 µg/mL; MIC90 range, 0.047-0.094 µg/mL). Results from the ex vivo keratitis model showed a statistically significant decrease in MRSA counts (0.5-2 log10 CFU/g; P <0.05) in corneas treated with 0.3% gemifloxacin every 30 min for 7 h. Moreover, the dose-response effect of different concentrations of gemifloxacin (3-3000 µg/mL) demonstrated that a dose of 30 µg/mL had the same efficacy as the highest dose of 3000 µg/mL against all S. aureus strains. Possibly, gemifloxacin reached a steady-state level in the cornea, as the fourth-generation fluoroquinolones have better anterior chamber penetration. This study demonstrated that 0.3% gemifloxacin ophthalmic solution may be an effective topical therapy for the treatment of MRSA keratitis. In addition, this reproducible, ethical and economic ex vivo infection model can be used as a mechanistically-based alternative to in vivo animal testing, bridging the gap between in vitro and in vivo results.