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Paulo J. Bispo, Darlene Miller; Heterogeneous Vancomycin-Intermediate Staphylococci Isolates from Endophthalmitis. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6197.
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To investigate the frequency of heterogeneous vancomycin-intermediate (hVI) staphylococci among endophthalmitis isolates.
A total of 121 isolates (vancomycin MICs of 0.75 to 2 µg/ml for S. aureus and 0.75 to 3 µg/ml for coagulase-negative staphylococci) collected between 2005-2010 were screened using brain heart infusion agar containing 4 µg/ml of vancomycin for selection of isolates with reduced susceptibility. Isolates selected by agar screening were further evaluated using the modified vancomycin population analysis profile (PAP) - area under curve (AUC) ratio method. PAP-AUC ratio of ≥ 0.9 between isolates and the control heterogeneous vancomycin-intermediate S. aureus - hVISA (Mu3) was used as criteria for confirmation of hVIS staphylococci isolates. Vancomycin and teicoplanin MICs for the parents and subpopulation isolates were determined by reference microbroth dilution. Accessory gene regulator (agr)-typing was also performed for the hVISA isolates.
In total, 22 out 121 isolates (18.2%) with reduced vancomycin susceptibility were selected by agar screening including 17 S. epidermidis, 2 S. warneri, and 1 isolate of each following species, S. aureus, S. haemolyticus and S. saprophyticus. Vancomycin susceptibility for parents and subpopulation isolates was similar (all susceptible). For teicoplanin, 3 parents and 9 subpopulations of S. epidermidis isolates were intermediate-resistant. Using the PAP-AUC ratio criteria, the overall prevalence of hVI staphylococci isolates was 5% (6 out 121). Those isolates included 5 S. epidermidis (out 17 tested) and 1 methicillin-susceptible S. aureus. The heterogeneous vancomycin-intermediate S. epidermidis (hVISE) isolates were all resistant to ciprofloxacin and belonged to the agr groups II (n=4) and I (n=1).
Our results show that heterogeneous intermediate-resistance to vancomycin has emerged among S. aureus and S. epidermidis from endophthalmitis. These isolates were also co-resistant to fluoroquinolones. Such a combination of resistance phenotypes could lead to poorer patient outcomes and may constitute an emerging concern for the management of staphylococcal endophthalmitis.
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