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Frank A Bucci, Christine M Sanfilippo, Heleen H DeCory, Loretta Amico, Ruth E Evans, Timothy L Comstock; Antibacterial Susceptibility of Coagulase Negative Staph Before and After Prophylactic Use of Besifloxacin and Moxifloxacin. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1489.
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We previously reported that prophylactic use of besifloxacin 0.6% (BESI) or moxifloxacin 0.5% (MOXI) QID for 3 days led to significant reductions in lid CFUs of commensal bacteria, but only BESI produced significant reductions in lid CFUs 1 hr after a single treatment. BESI also led to more rapid and significant elimination of methicillin resistant (MR) Staphylococcus epidermidis. Here we report in vitro susceptibilities to BESI and comparator antibacterials of commensal coagulase negative staphylococci (CoNS) from this study before and after treatment.
Patients were randomized to BESI or MOXI QID for 3 days prior to cataract surgery in their surgical eye, and 1 hr prior to a final culture in their non-surgical eye, on the day of surgery. Lid and conjunctival cultures were obtained from both eyes before (V1) and after treatment (V2). Samples were submitted to a central laboratory for enumeration, species identification, and susceptibility testing. Minimum inhibitory concentrations (MICs) were determined by broth microdilution for a panel of comparator antibacterials including BESI and MOXI.
Data from 63 patients were analyzed. Prior to treatment, the predominant bacteria on both conjunctiva and lids were CoNS. BESI had the lowest MIC90 against CoNS (0.5 µg/mL), lower than that of vancomycin (2 µg/mL). Against MR-CoNS, the MIC90 of BESI was 8- to 64-fold lower than that of other fluoroquinolones (MOXI, gatifloxacin, levofloxacin, ciprofloxcin). Fewer BESI-treated eyes harbored CoNS at V2 compared to MOXI-treated eyes, with a significant difference between treatments for lids (P<0.05). In BESI-treated eyes, nearly all V2 isolates were either a new colonizing CoNS not present at V1 or the V1 CoNS species present at reduced CFUs. In several MOXI-treated eyes, the V2 CoNS was the same species as the V1 isolate at unchanged or increased CFUs—in many of these cases (n=11 isolates, 8 patients) the isolate had an MIC predictive of intermediate/full resistance to MOXI.
BESI demonstrated the strongest in vitro potency against commensal CoNS in this study and was more effective than MOXI in decreasing the bacterial load on the lids and conjunctiva. Several MOXI-treated eyes had unchanged or increased bacterial loads attributable to the presence of MOXI-resistant CoNS.
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