This study reports two novel selective differential media. A first differential medium can be applied in methods for the isolation of non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes (O26, O103, O111 and O145) from food or faeces. A second differential medium was designed for both sorbitol-positive and -negative O157 STEC strains. Selective differential media are based on a chromogenic compound to signal beta-galactosidase activity and one or more fermentative carbon sources. The chromogenic marker and carbohydrates were combined with a pH indicator and several inhibitory components, which resulted in highly specific differentiation media. Consecutive use of a serotype-dependent choice of confirmation media resulted in a very low incidence of false-positive isolates when comparing clinical STEC strains with a collection of commensal E. coli strains.

In October 2007, an outbreak of verocytotoxin-producing Escherichia coli (VTEC) O145 and E. coli O26 occurred among consumers of ice cream produced and sold in September 2007 at a farm in the province of Antwerp (Belgium). The ice cream was consumed at two birthday parties and also eaten at the farm. Five children, aged between two and 11 years, developed haemolytic uraemic syndrome (HUS), and seven other co-exposed persons contracted severe diarrhoea. In three of the five HUS cases VTEC O145 infections were laboratory confirmed, one in association with VTEC O26. Identical isolates of E. coli O145 and O26 were detected with PCR and PFGE in faecal samples of patients and in ice cream leftovers from one of the birthday parties, in faecal samples taken from calves, and in samples of soiled straw from the farm at which the ice cream was produced. Ice cream was made from pasteurised milk and most likely contaminated by one of food handlers.

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Aims:  A range of new differential and confirmation plating media for some non‐O157 Shiga toxin producing Escherichia coli (STEC) serotypes (O26, O103, O111, O145) and both sorbitol‐positive and ‐negative O157 were evaluated using artificially contaminated samples. Methods and Results:  Dairy products (raw milk, cheese made from pasteurized milk and raw milk), meat (ground beef, fermented meat) and cattle faeces were artificially contaminated using clinical STEC strains. Isolation efficiency was 100%, 82·3%, 88·5%, 65·9%, 64·3% and 15·8%, respectively, for an inoculum size of ≤100 CFU 25 g−1. The consecutive use of differential and confirmation media limited the incidence of false positive isolates from 0% for raw milk samples, cheese made from pasteurized milk and for fermented meat to 2·1% for cheese made from raw milk, and to 8·9% for ground beef. Conclusions:  Data presented in this paper indicated that the efficiency of the applied isolation method was dependent on sample‐to‐sample variation but not on the inoculum size. Significance and Impact of Study:  Data in this paper indicated that isolation of low levels of non‐O157 and sorbitol‐positive O157 STEC from food samples is possible.

In September-October 2007, a mixed-serotype outbreak of verocytotoxin-producing Escherichia coli (VTEC) O145:H28 and O26:H11 occurred in the province of Antwerp, Belgium. Five girls aged between 2 and 11 years developed hemolytic uremic syndrome, and seven other coexposed persons with bloody diarrhea were identified. Laboratory confirmation of O145:H28 infection was obtained for three hemolytic uremic syndrome patients, one of whom was coinfected with O26:H11. The epidemiological and laboratory investigations revealed ice cream as the most likely source of the outbreak. The ice cream was produced at a local dairy farm using pasteurized milk. VTEC of both serotypes with indistinguishable pulsed-field gel electrophoresis patterns were isolated from patients, ice cream, and environmental samples. Quantitative analysis of the ice cream indicated concentrations of 2.4 and 0.03 CFU=g for VTEC O145 and O26, respectively. Virulence typing revealed that the repertoire of virulence genes carried by the O145:H28 outbreak strain was comparable to that of O157 VTEC and more exhaustive as compared to the O26:H11 outbreak strain and nonrelated clinical strains belonging to these serotypes. Taken together, these data suggest that O145:H28 played the most important role in this outbreak.