Evaluation of errors during susceptibility reporting of glycopeptide antibiotics for enterococcal isolates on sole basis of widely used disk diffusion test

Abstract

In resource limited settings, very often susceptibility reports glycopeptide antibiotics are released only on the basis of disk diffusion test. Determination of MIC by either E-strips or microbroth dilution tests can be of paramount importance in checking the errors that may have incurred with the singular use of disk diffusion tests. Distribution of errors in Vancomycin and Teicoplanin susceptibility reporting by disk diffusion test was evaluated in comparison with MIC determination with reference method of E-strip. A total of 40 isolates of Enterococcus species were obtained during the study period. In vancomycin susceptibility reporting, very major errors, major errors and minor errors were observed in 33.3%, 5.4% and 5% instances respectively. For teicoplanin, major errors were observed in 5.3% of instances. E test can be used in conjunction with disk diffusion where resources are limited. We have observed that by using a combination of both disk diffusion and MIC determination by E-strip methods for glycopeptide antibiotics, a majority of reporting errors can be addressed.