COMPARATIVE EFFICACY OF TOPICAL CIPROFLOXACIN FOR TREATING MYCOBACTERIUM-FORTUITUM AND MYCOBACTERIUM-CHELONAE KERATITIS IN AN ANIMAL-MODEL

Mycobacterium fortuitum and M. chelonae are the two most common causes of nontuberculous mycobacterial keratitis, and they may be difficult to differentiate at diagnosis. Mycobacterium fortuitum is generally mo re sensitive to ciprofloxacin in vitro than is M. chelonae. Using a ra bbit model, we compared the efficacy of topical ciprofloxacin (3 mg/ml ) against M. chelonae keratitis to its efficacy against M. fortuitum k eratitis. After four days of therapy, ciprofloxacin significantly redu ced the number of both organisms in treated eyes compared to Untreated control eyes (both P values < .001). Mean culture ratios (colony-form ing,units in treated eye divided by colony-forming units in untreated eye for each rabbit) were used to compare efficacy between groups. Whe n all treated animals were considered, no significant difference was f ound between groups (P = .13). When outlier values were exclude;ii cip rofloxacin was more effective against M. fortuitum than M. chelonae (P = .01). When treated and untreated eyes were compared after therapy i n the M. fortuitum group, ciprofloxacin treatment was associated with a reduction in mean stromal infiltrate area (P = .03) and in the tende ncy to form satellite lesions (P = .07). A clinical effect was not obs erved in the M. chelonae group. Although ciprofloxacin is effective ag ainst both organisms, it appears to be less effective against M. chelo nae than M. fortuitum in vivo.