Detection of vancomycin resistance in enterococci by the Vitek AMS system

The ability of the Vitek AMS system to detect vancomycin resistance in enterococci was evaluated by comparing the results to an agar dilution screen method. Of 100 strains tested, 43 were resistant and 51 were susceptible by both tests. Two strains were intermediate by Vitek but susceptible by agar screen, one was intermediate by Vitek but resistant by agar screen, and four were susceptible by Vitek but resistant by agar screen. When the Vitek intermediate and resistant results were combined, the false resistant rate was 4.4% and false susceptible rate was 8.5%. In its current format, the Vitek system appears not to have acceptable accuracy for the detection of vancomycin resistance in enterococci.