[Evaluation of a new disk containing indoxyl-beta-D-glucuronide for rapid identification of Escherichia coli]

To establish a simple identification procedure for Escherichia coli, we developed a disk containing indoxyl-beta-D-glucuronide, the chromogenic substrate of beta-D-glucuronidase. Of 188 isolates of Enterobacteriaceae, 101 (97%) of 104 strains of E. coli and two (67%) of three strains of Shigella species were positive for beta-glucuronidase. We also tested 495 strains (466 strains of E. coli and 29 of Citrobacter freundii) that might be considered lactose-fermenting E. coli under routine conditions, and 458 strains of E. coli showed beta-glucuronidase activity: the sensitivity of the disk method was 92%, specificity was 100%, and the negative predictive value was 44%. Our results suggest that for routine identification of E. coli on primary isolation plates, the disk method is sufficiently rapid (within 3h), simpler, and far less costly than identification methods using commercially available kits.