Article

Emerging 8-Methoxyfluoroquinolone Resistance among Methicillin-Susceptible S. epidermidis Endophthalmitis Isolates.

Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami-Miller School of Medicine, Miami, FL 33136, USA.
Journal of clinical microbiology (Impact Factor: 4.23). 07/2013; 51(9). DOI: 10.1128/JCM.00846-13
Source: PubMed

ABSTRACT Fluoroquinolones remain the most commonly used antimicrobials for the prevention and management of bacterial endophthalmitis. Coagulase negative Staphylococci are the most frequently recovered pathogens. Increasing resistance among this group has paralleled the presence of methicillin resistant. From 2005 to 2010, we recovered 38 methicillin-susceptible Staphylococcus epidermidis (MSSE) from endophthalmitis cases at our Institute, including15 (39.5%) isolates resistant to gatifloxacin and moxifloxacin members of the C-8-methoxyfluoroquinolones family. Mutations in the quinolone resistance determining regions (QRDR) of gyrA and parC were determined and correlated with fluoroquinolones minimal inhibitory concentrations using Etests for these 15 MSSE isolates. High-level resistance (MIC >32 μg/ml) to gatifloxacin and moxifloxacin was documented for 46.7% of the MSSE isolates and low-level resistance (MICs 2 to 4 μg/ml) for 53.3%. MIC for ciprofloxacin, levofloxacin and ofloxacin was >32 μg/ml for all isolates. The amino acid substitution Ser84Phe in gyrA was found among all isolates. A second mutation in gyrA (Glu88Lys) resulted in high-level resistance to moxifloxacin and gatifloxacin. Almost all (92.8%) isolates presented double point mutations in parC gene at codons 80 and 84 with different combinations. Eighty seven percent of the patients had prior exposure to topical 8-methoxyfluoroquinolones. Prior exposure to the 8- methoxyfluoroquinolones may contribute to the selection of MSSE strains containing multiple mutations in the QRDR of gyrA and parC that results in low- and high-level resistance to these agents.

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