PROBLEMS IN THE RECOVERY AND IDENTIFICATION OF ENTEROPATHOGENIC ESCHERICHIA COLI FROM FOODS

Abstract

During a recent outbreak of gastroenteritis associated with serogroup 0124:B17 of Escherichia coli, various problems complicated recovery and identification of the pathogen. Standard methods for E. coli were of limited value because of atypical behavior of isolates. Two modified recovery procedures have been presented. For rapid lactose fermenters, pre-enrichment in MacConkey broth with subsequent transfer to lauryl sulfate tryptose broth and incubation at 44 C is recommended. For slow lactose fermenters, pre-enrichment in nutrient broth with subsequent transfer to Mossel's enteric enrichment broth and incubation at 41.5 C is tentatively proposed. Isolation agars include Levine's eosin methylene blue for lactose fermenters and MacConkey agar for non-lactose fermenters. The merits of a direct streak are considered. To facilitate rapid differentiation of E. coli from closely related Enterobacteriaceae within 3 days a modified Lundbeck procedure is offered. Isolates are first screened for H2S formation, indole production, arabinose fermentation, urease and ONPG-ase. Secondary characterization based on results of the indole and TSI reactions includes Voges-Proskauer test (22 C), lysine decarboxylase activity, KCN tolerance, and fermentation of adonitol, cellobiose, sorbitol, or glucose. Confirmation by gram-reaction nitrate reduction, and cytochrome oxidase activity is required to differentiate from members of other families. Critical factors of serological analysis are stressed. Prospects for future research are discussed.