Ocular Bacteria From Conjunctivitis Patients: Susceptibility to Gatifloxacin and Older Fluoroquinolones

Abstract

Abstract: : Purpose:To evaluate susceptibility of ocular isolates from bacterial conjunctivitis patients to gatifloxacin, a new ophthalmic fluoroquinolone, using levofloxacin and ciprofloxacin as comparator antimicrobials. Methods:Conjunctival swabs were taken prior to any antibacterial therapy from patients diagnosed with bacterial conjunctivitis participating in a clinical trial of gatifloxacin. MICs for independent bacterial isolates from the swabs were classified using NCCLS susceptibility breakpoints. Results:All Gram-positive ocular isolates (n=170) were susceptible to gatifloxacin, except for a single strain of Staphylococcus haemolyticus which displayed intermediate resistance. In contrast, 2.9% of Gram-positive isolates were resistant to levofloxacin and 7.6% were resistant to ciprofloxacin. All isolates of Staphylococcus epidermidis (n=38), a species frequently encountered in ocular infections, were susceptible to gatifloxacin. However, 10.5% of S. epidermidis ocular isolates were resistant to levofloxacin and 15.8% to ciprofloxacin. Another 5.3% showed intermediate resistance to levofloxacin. The gatifloxacin MIC₉₀ for S. epidermidis ocular isolates was 2.0 µg/mL, compared to 8.0 µg/mL for levofloxacin and 32 µg/mL for ciprofloxacin. For Streptococcus pneumoniae (n=30), the gatifloxacin MIC₉₀ was 0.25 µg/mL, compared to 1.0 µg/mL for levofloxacin and ciprofloxacin. All Gram-negative isolates (n=65) were susceptible to all 3 antibacterials. Conclusions:Substantial percentages of Gram-positive species isolated from bacterial conjunctivitis patients in this study were resistant or intermediately resistant to levofloxacin and ciprofloxacin; however, the same isolates were susceptible to gatifloxacin. MIC₉₀ values for the most commonly encountered species of Gram-positive ocular pathogens favored gatifloxacin by 4-fold to 16-fold. Compared to older fluoroquinolones, gatifloxacin displays clearly improved activity against Gram-positive ocular bacteria in vitro.

Keywords: antibiotics/antifungals/antiparasitics • clinical (human) or epidemiologic studies: tre • conjunctivitis