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Avinash Pathengay, Darlene Miller, Harry W. Flynn, Jr.; In Vitro Vancomycin Concentrations Required To Inhibit Methicillin Resistant Coagulase Negative Staphylococci Recovered From Endophthalmitis Isolates. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2972.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the increase in vitro vancomycin’s minimum inhibitory concentrations (MIC) required to inhibit methicillin resistant Coagulase negative staphylococcus (MRCNS) isolates recovered from endophthalmitis.
We reviewed and compared MICs distributions and inhibition percentages for MRCNS isolated from endophthalmitis during 1990-1999 (baseline) versus isolates recovered during 2000-June 30, 2010.
Methicillin resistance among CNS increased from 36% (86/285) in 1990-1999 to 46%,(100/217) in 2000-2010. The vancomycin (MIC90) for all MRCNS isolates (N=186), 1990-2010 was 2 µg/ml, with 57% (N=106) of the isolates inhibited at a vancomycin concentration of ≤ 1 µg/ml. The MIC90 for isolates recovered during 1990-1999 (N=86) was 1 µg/ml with 95% of the isolates inhibited at this value. MIC90 for the most recent period (2000-2010 N=100)) increased to 2 µg/ml with only 25% of isolates inhibited at a concentration of ≤ 1 µg/ml.Among aqueous isolates (N=39), MIC90 for all aqueous isolates increased from 1 to 2 µg/ml with 95% of isolates inhibited by a vancomycin concentration of ≤1 µg/ml for the period 1990-1999 (N=19) versus only 30% of isolates for 2000-2010 (N=20).Among vitreous isolates (N=147), MIC90 for vitreous isolates also doubled between periods ( 1 vs2 µg/ml). At baseline, 95% of vitreous isolates were inhibited by a MIC of ≤ 1 µg/ml, but was reduced to 22% for 2000-2010.
In the current study vancomycin MIC creep occurred among MRCNS isolates recovered from endophthalmitis over a 20 year period. An elevated vancomycin MIC within the susceptible range may reduce vancomycin in vitro efficacy, and impact clinical outcomes. Clinical laboratories should adopt methods to monitor changes in vancomycin MIC distributions.
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