Ciprofloxacin and levofloxacin resistance among methicillin-sensitive Staphylococcus aureus isolates from keratitis and conjunctivitis

PURPOSE: The majority of Staphylococcus aureus isolated from ocular infections are methicillin sensitive (MSSA). Fluoroquinolone resistance among methicillin-resistant Staphylococcus aureus is well known but not among MSSA. In this study we investigate the emergence of fluoroquinolone (ciprofloxacin, levofloxacin) resistance among methicillin-sensitive Staphylococcus aureus isolates from keratitis and conjunctivitis. DESIGN: Cross-sectional study. METHODS: Minimal inhibitory concentration susceptibility profiles for 1230 S. aureus isolates from keratitis and conjunctivitis were analyzed. Historical and current rates of emerging fluoroquinolone resistance for methicillin resistant (MRSA) and methicillin-sensitive isolates (MSSA) were evaluated. Sensitivity patterns for vancomycin and gentamicin were also documented. RESULTS: Ciprofloxacin resistance among corneal and conjunctival S. aureus isolates during the first 6 years after its introduction (baseline) (1990-1995) was 8% and ranged from 3% to 11%. The rate for the most recent 6 years (current) (1996-2001) was 20.7%. Baseline ciprofloxacin resistance for MSSA isolates was 2% vs 55.8% for MRSA. The current resistance rate for MSSA is 5% vs 83.7% for MRSA. The general resistance rate from January 2000 to December 2001 for levofloxacin was 25.5% vs 33.2% for ciprofloxacin (P =.13). The levofloxacin-resistance rate for MSSA was 4.7% vs 11.9% for ciprofloxacin (P =.05). In MRSA isolates, a higher resistance rate was found for ciprofloxacin (95.7%) vs levofloxacin (82.1%) (P =.04). No resistance for vancomycin was documented for any of the S. aureus isolates. Gentamicin susceptibility for MSSA was 99% and MRSA was 86%. CONCLUSIONS: Ciprofloxacin and levofloxacin resistance among methicillin sensitive S. aureus corneal and conjunctival isolates is increasing. This is of concern because it narrows treatment choices for the management of these common ocular infections. (C) 2004 by Elsevier Inc. All rights reserved.