Fluoroquinolone therapy in a rabbit model of post-LASIK methicillin-resistant Staphylococcus aureus keratitis

Abstract

Purpose: To develop a rabbit model of post-laser in situ keratomileusis (LASIK) methicillin-resistant Staphylococcus aureus (MRSA) keratitis for studying fluoroquinolone prophylaxis and treatment.

Setting: Department of Microbiology, University of Mississippi Medical Center, Jackson, Mississippi, USA.

Methods: An MRSA keratitis isolate (5 microL, 500 colony forming units [CFU]) was inoculated underneath a corneal flap. Bacterial growth and pathology were determined by quantitative cultures (CFU) and slitlamp examination, respectively. The effectiveness of commercial moxifloxacin and gatifloxacin formulations was compared in 3 regimens: prophylaxis (4 drops before inoculation), early therapy (single drop hourly from 4 to 9 hours postinfection), and late therapy (single drop hourly from 10 to 15 hours postinfection). Zones of bacterial inhibition to known in vivo antibiotic concentrations were determined.

Results: Bacteria grew to a maximum of approximately 10(6) CFU/cornea within 10 hours postinfection. The slitlamp examination scores showed pathologic changes beginning 10 hours postinfection and progressed throughout the infection. For prophylaxis, eyes treated with moxifloxacin had significantly fewer CFU than gatifloxacin-treated eyes or untreated controls (both P < or = .0001). During early treatment, the antibiotics were equally effective in reducing CFU relative to untreated controls (P < or = .0001). In late treatment, gatifloxacin and moxifloxacin caused significant reductions in CFU relative to untreated controls (P < or = .0007 and P < or = .0001, respectively). Moxifloxacin produced zones of bacterial inhibition significantly larger than those produced by gatifloxacin.

Conclusions: Methicillin-resistant S aureus inoculation beneath a rabbit corneal flap produced an infection that was useful for quantitative microbiological studies. A significant advantage in using moxifloxacin relative to gatifloxacin was observed in prophylaxis of keratitis (P = .0001).