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: 3.99). 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 resistance. From 2005 to 2010, we recovered 38 methicillin-susceptible Staphylococcus epidermidis (MSSE) isolates from endophthalmitis patients at our institute, including 15 (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 fluoroquinolone MICs based on Etests of 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
(MIC, 2 to 4 μg/ml) was determined for 53.3%. The MICs for ciprofloxacin, levofloxacin, and ofloxacin were >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 the 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 QRDRs of gyrA and parC that results in low- and high-level resistance to these agents.

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Available from: Harry W Flynn, Aug 18, 2014
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