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

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Abstract

Purpose

The majority of Staphylococcusaureus isolated from ocular infections are methicillin sensitive (MSSA). Fluoroquinolone resistance among methicillin- resistant Staphylococcusaureus is well known but not among MSSA. In this study we investigate the emergence of fluoroquinolone (ciprofloxacin, levofloxacin) resistance among methicillin-sensitive Staphylococcusaureus 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.

Section snippets

Design

A retrospective, cross-sectional study to evaluate resistance to fluoroquinolones (ciprofloxacin and levofloxacin) among methicillin-sensitive SA isolates.

Methods

The Microbiology Laboratory Database was searched to identify SA isolates recovered from bacterial conjunctivitis and keratitis during the 12-year period 1990 to 2001. Corneal and conjunctival cultures were performed in all cases according to standard microbiologic protocols.21 Specimens for culture were obtained by scraping with a blade or spatula. The following media were inoculated: blood agar, chocolate agar, Sabouraud agar, and thioglycollate broth. The criteria used to consider a culture

Results

During the twelve-year study period from 1990 through 2001, 1230 cultures positive for SA from keratitis and conjunctivitis were identified. Staphylococcus aureus isolates constituted 62% (500/806) of the total corneal pathogens for the first 5 years of the study (1990–1994). In the last 2 years (2000–2001), the rate was 65% (181/276). The number of SA isolates seen each year was similar, ranging from 80 to 120 isolates, (103 ± 11.5 isolates). The percentage of MSSA seen each year declined

Discussion

Methicillin-sensitive isolates account for the majority of SA ocular infections. At least 80% of MSSA in this study period remained susceptible to the quinolones. The decline in susceptibility to the quinolones is of concern because it narrows treatment choices for the management of these common and often debilitating ocular infections.

Although we have witnessed a significant increase in the resistance to the fluoroquinolones, Tuft and Matheson from London reported in 2000 that ofloxacin was

Supplementary files

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