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In Vitro Fluoroquinolone Resistance in Staphylococcal Endophthalmitis Isolates
Darlene Miller, DHSc, MPH;
Patrick M. Flynn;
Ingrid U. Scott, MD, MPH;
Eduardo C. Alfonso, MD;
Harry W. Flynn, Jr, MD
Arch Ophthalmol. 2006;124:479-483.
Objective To evaluate the in vitro susceptibility and cross-resistance of gatifloxacin and moxifloxacin vs older fluoroquinolones among coagulase-negative staphylococci recovered from patients with clinical endophthalmitis.
Methods A combination of E tests and disk diffusion methods was used to determine in vitro susceptibility and cross-resistance for 111 coagulase-negative staphylococci isolates recovered during a 15-year period (January 1, 1990, to December 31, 2004) against 5 fluoroquinolones.
Results In vitro susceptibilities (percentage sensitive) in descending order were as follows: gatifloxacin, 74.5%; moxifloxacin, 72.1%; levofloxacin, 69.3%; ciprofloxacin, 65.6%, and ofloxacin, 60.4%. More than 65% of the coagulase-negative staphylococci resistant to ciprofloxacin (n = 38) demonstrated in vitro cross-resistance to gatifloxacin (25 [65.8%] of 38) and moxifloxacin (27 [71.1%] of 38). During the initial 5 years (January 1, 1990, to December 31, 1994), 96.6% of the coagulase-negative staphylococci were sensitive to gatifloxacin and moxifloxacin, with minimal inhibitory concentration required to inhibit or kill 90% of the isolates of 0.19 µg/mL and 0.12 µg/mL, respectively. During the last 5-year period (January 1, 2000, to December 31, 2004), the percentage of sensitive coagulase-negative staphylococci declined to 65.4% for gatifloxacin and moxifloxacin (P=.02). Minimal inhibitory concentration required to inhibit or kill 90% of the isolates was 32 µg/mL or greater for both drugs.
Conclusions Gatifloxacin and moxifloxacin demonstrated an in vitro efficacy of less than 80% for coagulase-negative staphylococci endophthalmitis in the present study. Ciprofloxacin resistance may serve as a surrogate for concurrent in vitro resistance for gatifloxacin and moxifloxacin. Resistance increased significantly during the last 5 years. Declining in vitro susceptibility to gatifloxacin and moxifloxacin may have important implications for the prevention and treatment of postoperative endophthalmitis.
Author Affiliations: Departments of Ophthalmology, Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, Fla (Drs Miller, Alfonso, and Flynn and Mr Flynn), and Penn State College of Medicine, Hershey, Pa (Dr Scott).
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