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D. Miller, E. Alfonso, M. Diaz, E. Perez; Reduced Glycopetide and Mupirocin Susceptibility Among Ocular Staphylococci. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1989.
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Gram positive isolates are the most common pathogens recovered from ocular infectious diseases. Glycopeptides remain antibiotics of last resort for the treatment of these infections. The focus of this study was to report reduced in vitro susceptibility to glycopeptide antibiotics among ocular staphylococci from keratitis and endophthalmitis and to evaluate the in vitro susceptibility of mupirocin to inhibit or kill these isolates.
Vancomycin susceptibility MIC distribution data for Staphylococcus aureus, Coagulase Negative Staphylococci (CoNS), were collected and compared for time periods 1990-1994, 1995-1999, 2000-2004, and 2005-11-30, 2007. MICs were determined using the Vitek Auto Microbial System and E tests. MIC concentrations ranged from 0.25 ug-32 ug/ml (vitek) and 0.016-256 ug/ml for the E tests. Susceptible MICs were ≤2 ug/ml for S. aureus and ≤4 ug/ml for Coagulase Negative Staphylococci. Staphylococci isolates were also screened for hetero ( 1-4 ug/ml), intermediate (8-16 ug/ml) and high level glycopeptide resistance (≥ 32) using the E test macromethod (EMAC) (N=96) and glycopeptide resistance detection strips (EGRD, n=94). E tests were used to detected mupirocin resistance ( ≥ 512,n=91).
Modal MIC (MIC50)-≤1 ug/ml and MIC90 (2 ug/ml) for S. aureus remain stable from baseline (1990-1994, N=634) to the current period (N=515). At baseline 98% of isolates were susceptible to a vancomycin concentration of ≤1 ug/ml, but declined to 62% for the current period. At baseline 94% of CoNS isolates (N=125) were inhibited by <1 ug/ml, but only 20% were susceptible during 2005-November 2007 (N=67). Low level resistance was detected in 80% of the staphylococci isolates with both screening methods. Hetero-resistance ranged from 2.1% (EMAC) to 4.2% (EGRD) and were highest for CoNS (43.7) and MRSA (5.3%). High level mupirocin resistance was detected in 27.5% of the staphylococcal isolates, 41.9%-CoNS, 32.1%-MRSA and 9.4%-MSSA.
. Reduced glycopeptide susceptibility was confirmed in at least 80% of evaluated staphylococcal isolates. The impact of these results on clinical outcomes needs investigation.
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