Acceptable performance of VITEK 2 system to detect extended-spectrum beta-lactamases in clinical isolates of Escherichia coli: a comparative study of phenotypic commercial methods and NCCLS guidelines.

The disk approximation method, Etest (AB Biodisk, Solna, Sweden), and VITEK 2 system (bioMérieux, Marcy l'Etoile, France) were used to study 399 extended-spectrum beta-lactamase (ESBL)-producing (115 strains) and non-ESBL-producing (284 strains) clinical isolates of Escherichia coli after recommended procedures. Comparative study of the phenotypic findings yielded data on the sensitivity, specificity, and positive and negative predictive values and performance of each method. The sensitivity (100% using 2 substrates), specificity (99.3-100%), and predictive values of the disk approximation, Etest, and VITEK 2 methods were similar.