Efficacy of Daptomycin on Experimental Methicillin-Resistant Staphylococcus aureus Keratitis in Rabbits

Purpose: We aimed to compare the efficacy of topical daptomycin (DAP) with that of vancomycin (VA) in the treatment of keratitis caused by methicillin-resistant Staphylococcus aureus (MRSA). Methods: One hundred colony-forming unit MRSA bacteria were injected intrastromally into both corneas of 28 rabbits. Sixteen hours after injection, the rabbits' eyes were treated with 1 drop of topical DAP (10 or 50mg/mL), VA (50mg/mL), or isotonic saline for 19 doses. Their eyes were examined for clinical severity before and after treatment. Results: The minimum inhibitory concentration values of VA and DAP against the bacterial strain were found to be 2 and 0.5g/mL, respectively. The mean pre- and post-treatment clinical scores of the eyes did not differ significantly among the groups. However, the mean difference between the post- and pretreatment clinical scores was significantly lower in the 50mg/mL DAP group than in the other groups (P=0.042). A marked decrease in bacterial load was detected in all treatment groups compared to the control group (P=0.002). Although there were no significant differences in bacterial load among the treatment groups, the 50mg/mL DAP group showed the greatest decrease. The mean % epithelial erosion rate tended to be higher in the 50mg/mL VA group than in the other groups (P=0.31). Conclusions: Topical DAP significantly reduced the bacterial load and showed activity against MRSA comparable to that of fortified VA in this experimental model.