Vancomycin mic changes in methicillin-resistant staphylococcus aureus (MRSA) blood culture isolates

Abstract

AimVarious levels of reduced susceptibility to glycopeptides are emerging with increasing frequency in Staphylococcus aureus (S. aureus) strains. We aimed to determine Vancomycin minimum inhibitory concentration (MIC)s for Methicillin-resistant S. aureus (MRSA) strains isolated from blood cultures between 2012-2015 and to evaluate changes in Vancomycin MIC levels over the years (2007-2015) at our institution.MethodA total of 45 MRSA blood culture isolates between 2012 and 2015 were studied. MIC de-terminations for Vancomycin were performed using Etest method. The mean MIC and geometric mean MIC were calculated for each year and the differ-ences between the years were analyzed. These results were then evaluated together with the results of our previous study performed between 2007 and 2011.ResultsThere was no Vancomycin-resistant S. aureus (VRSA) or Vancomycin-intermediate S. aureus (VISA) among the isolates. Only one strain was evaluated as hetero-resistant Vancomycin-intermediate S. aureus (hVISA). When compared, there were significant differences between the years (2012-2015) for the mean MICs (p=0.027) and the trend in the increase in the Vancomycin mean MICs over the years was found to be significant (p=0.005). When the results of both studies were evaluated together, there were significant differences between the years (2007-2015) for the mean MICs (p=0.001) and the upward trend in the Vancomycin mean MICs over the years was found to be significant (p<0.001).ConclusionWe observed an increase in Vancomycin MICs for MRSA blood culture isolates over the years at our hospital. It is important to monitor local Vancomycin MICs in invasive MRSA isolates systematically.

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