Comparison of topical antibiotics for treating Mycobacterium chelonae keratitis in a rabbit model

To investigate the effect of topical amikacin (25 mg/ml), imipenem (25 mg/ml), ciprofloxacin (3 mg/ml), clarithromycin (20 mg/ml), amikacin combined with ciprofloxacin, amikacin combined with imipenem, and amikacin combined with clarithromycin on Mycobacterium chelonae keratitis.

Ninety New Zealand albino rabbits were infected with a strain of M. chelonae for which minimum inhibitory concentration indicated in vitro sensitivity to the above antibiotics. The rabbits were treated for one or two weeks. The treatment efficacy was judged by the size of stromal infiltrate and quantitative culture of the infected corneas.

The size of the stromal infiltrate showed no significant difference in treated eyes compared to the untreated, control eyes. However, all treatments significantly reduced the number of organisms in treated eyes compared to untreated, control eyes (all p-values < 0.05). No significant difference in treatment efficacy was found between individual treatment groups. In none of the cases were organisms eliminated from the infected eyes, even after 2 weeks of treatment.

The results suggest that topical amikacin, imipenem, ciprofloxacin and clarithromycin had some therapeutic effect on M. chelonae keratitis; however, amikacin combined with imipenem, ciprofloxacin, and clarithromycin showed no increased efficacy over single agent therapy during 2 weeks of treatment. Long term treatment may be required to eradicate M. chelonae.