Semi-automated antimicrobial susceptibility testing for VRE/VSE
Vancomycin-resistant Enterococcus faecium (VRE) is an increasingly important healthcare-associated pathogen. The mainstay for detection of VRE is phenotypic antimicrobial susceptibility testing (AST). In this study, we evaluated the performance of the two semi-automated systems BD Phoenix™ M50 (Becton Dickinson, Heidelberg, Germany) and VITEK®2 (bioMérieux, Nürtingen, Germany), and the EUCAST disk diffusion in detecting VRE, in comparison with vanA and vanB PCR. Sensitivity was 98.48 % for EUCAST disk diffusion, 92.37 %, for VITEK®2, and 86.36 % for BD Phoenix™ M50. 21 Twenty-one vanA or vanB positive isolates showed susceptible results in at least one phenotypic AST method in the presence of a vanA or vanB gene. Two isolates which showed susceptible results in disk diffusion and in semi-automated systems had a missing or incomplete vanS/vanR regulator system. 13Thirteen isolates had genotypic or phenotypic evidence for the presence of different strains with different susceptibility patterns within the clinical isolate. Using a mixed test inoculum of VSE and VRE, EUCAST disk diffusion was able to detect VRE at a proportion of 10 % within the total test inoculum, VITEK®2 required a proportion of 20 – 30 %, and BD Phoenix™ M50 was unable to detect VRE when there was a proportion of 10 % VSE within the total test inoculum. The VSE used in this experiment showed faster growth kinetics than the VRE. We conclude that EUCAST disk diffusion is the most reliable phenotypic AST method for detection of VRE, while semi-automated systems should be used in combination with other methods.
Vancomycin-resistant Enterococcus faecium (VRE) is an increasingly important healthcare-associated pathogen. The mainstay for detection of VRE is phenotypic antimicrobial susceptibility testing (AST). In this study, we evaluated the performance of the two semi-automated systems BD Phoenix™ M50 (Becton Dickinson, Heidelberg, Germany) and VITEK®2 (bioMérieux, Nürtingen, Germany), and the EUCAST disk diffusion in detecting VRE, in comparison with vanA and vanB PCR. Sensitivity was 98.48 % for EUCAST disk diffusion, 92.37 %, for VITEK®2, and 86.36 % for BD Phoenix™ M50. 21 Twenty-one vanA or vanB positive isolates showed susceptible results in at least one phenotypic AST method in the presence of a vanA or vanB gene. Two isolates which showed susceptible results in disk diffusion and in semi-automated systems had a missing or incomplete vanS/vanR regulator system. 13Thirteen isolates had genotypic or phenotypic evidence for the presence of different strains with different susceptibility patterns within the clinical isolate. Using a mixed test inoculum of VSE and VRE, EUCAST disk diffusion was able to detect VRE at a proportion of 10 % within the total test inoculum, VITEK®2 required a proportion of 20 – 30 %, and BD Phoenix™ M50 was unable to detect VRE when there was a proportion of 10 % VSE within the total test inoculum. The VSE used in this experiment showed faster growth kinetics than the VRE. We conclude that EUCAST disk diffusion is the most reliable phenotypic AST method for detection of VRE, while semi-automated systems should be used in combination with other methods.