Comparative in Vitro Activity of Levofloxacin, Ofloxacin, and Ciprofloxacin Against Ocular Streptococcal Isolates

Objective: To determine the in vitro efficacy of levofloxacin, ofloxacin, and ciprofloxacin against Streptococcus pneumoniae and Streptococcus viridans isolates recovered from clinical cases of keratitis and endophthalmitis. Methods: Streptococcal isolates recovered from keratitis and endophthalmitis cases between 1990 and 2001 were identified and extracted from the Microbiology Data Bank of the Bascom Palmer Eye Institute, Miami, FL. Comparative in vitro minimal inhibitory concentration (MIC₉₀) susceptibility profiles for levofloxacin, ofloxacin, and ciprofloxacin against a select group (n = 65) of streptococcal isolates were documented using the E test methodology. Penicillin susceptibility profiles were also evaluated. χ² 2 × 2 tables and McNemar's Paired-Sample Tests were used to established statistical significance. Results: MIC₉₀ values for levofloxacin, ofloxacin, and ciprofloxacin against pneumococcal isolates were 1.5, 6, and 3 μg/mL. The corresponding values for the S. viridans group were 2, 8, and 24 μg/mL. Levofloxacin was 4 times more active in vitro than ofloxacin and 2 times more active in vitro than ciprofloxacin against S. pneumoniae. Levofloxacin was 4 times more active in vitro than ofloxacin and 12 times more active than ciprofloxacin for S. viridans group. Sixty-three percent of the S. pneumoniae and 57.9% of the S. viridans group isolates were intermediate or resistant to penicillin. Levofloxacin provides 100% coverage for penicillin-intermediate and penicillin-resistant isolates versus 33.8% for ofloxacin and 29.2% for ciprofloxacin. Conclusion: Levofloxacin is highly active in vitro against streptococcal isolates recovered from keratitis and endophthalmitis patients, including penicillin-intermediate and penicillin-resistant strains.