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

Abstract

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). 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 50 mg/mL), VA (50 mg/mL), or isotonic saline for 19 doses. Their eyes were examined for clinical severity before and after treatment. The minimum inhibitory concentration values of VA and DAP against the bacterial strain were found to be 2 and 0.5 μg/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 50 mg/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 50 mg/mL DAP group showed the greatest decrease. The mean % epithelial erosion rate tended to be higher in the 50 mg/mL VA group than in the other groups (P=0.31). Topical DAP significantly reduced the bacterial load and showed activity against MRSA comparable to that of fortified VA in this experimental model.