Rapid identification of Escherichia coli with a fluorogenic beta-glucuronidase assay

We evaluated three fluorogenic methods (MUG; Remel, Lenexa, KS) for the rapid (less than 1 hr) identification of E. coli by detecting beta-glucuronidase activity. The methods included: direct disk inoculation test, tube test, and liquid spot reagent test. Fluorogenic tests were performed on pure cultures of lactose fermenters and compared with identification by Enterotube II (Roche Diagnostics; Nutley, NJ). Organisms yielding disparate results were further analyzed by API 20E (Analytab Products Inc.; Plainview, NY). The tube test was evaluated with isolates subcultured on both MacConkey and blood agars; the direct disk and liquid spot reagent methods were tested with isolates subcultured on blood agar only. All methods were highly specific (greater than 97%). Sensitivity of the beta-glucuronidase tests were method and media dependent, but exceeded 85% in all cases. The direct disk and tube tests also permitted detection of indole formation; results of indole testing, however, contributed little to accurately identifying E. coli.