Fluorogenic assay for rapid detection of Escherichia coli in food

Abstract

An assay procedure to screen for Escherichia coli in foods by using 4-methylumbelliferyl-.beta.-D-glucuronide (MUG) incorporated into lauryl tryptose (LST) broth was evaluated. The .beta.-glucuronidase produced by E. coli cleaves the MUG substrate to yield a fluorescent end product, E. coli-negative samples can be identified by lack of fluorescence in LST-MUG within 24 h, MUG was not inhibitory to colliforms and E. coli. Over 1,400 food and dairy samples were tested to compare the standard three-tube most-probable-number procedure with the MUG-containing or non-MUG-containing LST procedure. LST-MUG testing detected a greater nubmer of E. coli, with a lower false-positive rate (1.4%) and in a shorter time, than did the standard procedure. All false-positive results in the LST-MUG testing were attributable to .beta.-glucuronidase-producing staphylococci. No fasle-negative result was encountered. Use of MUG in LST broth obviates the EC broth step, allowing a 2.5-day procedure to a completed E. coli test versus the present 4- to 6-day standard most-probable-number method.