Kinetics of Killing of Ocular Isolates of Staphylococcus aureus and Staphylococcus epidermidis by Moxifloxacin

Abstract

Abstract: : Purpose:The Gram-positive staphylococci are the most frequently recovered bacteria from superficial ocular infections. Moxifloxacin is a fourth-generation fluoroquinolone antibiotic with superior activity against Staphylococcus aureus and Staphylococcus epidermidis . The purpose of this study was to define the kinetics of kill of moxifloxacin against ocular isolates of S. aureus and S. epidermidis. Methods:The kinetics of kill was measured in vitro by the reduction in CFU/ml as a function of time at 35°C. The two ocular staphylococcal isolates were susceptible to moxifloxacin and other quinolone antibiotics. Moxifloxacin was tested at two concentrations, 50 and 500 µg/mL. Results:At 50 µg/mL, moxifloxacin killed 3 logs (99.9%) of S. aureus in 30 minutes and 4 logs (99.99%) in 120 minutes. At the higher concentration level [500µg/mL] moxifloxacin killed 3 logs in 45 minutes and 4 logs in 180 minutes. Against S. epidermidis, moxifloxacin killed 3 logs in 50 minutes at 50 µg/mL and 4 logs in 180 minutes. Moxifloxacin at 500 µg/mL killed 3 logs in 85 minutes and 4 logs in 180 minutes. Conclusions: These in vitro kinetics of kill studies demonstrate that moxifloxacin rapidly kills two important Gram-positive bacterial pathogens, Staphylococcus aureus and Staphylococcus epidermidis . The speed of kill observed for moxifloxacin is faster than that for second-generation quinolones under the same test conditions.

Keywords: antibiotics/antifungals/antiparasitics • microbial pathogenesis: experimental studies • Staphylococcus