Screening of food raw materials for the presence of Shiga toxin-producing Escherichia coli O91:H21.

Aims:  To provide information on the prevalence and detection, in foods, of Shiga toxin-producing Escherichia coli (STEC) O91:H21. Methods and Results:  Seven hundred fifteen minced beef meats and 205 raw milk samples were analysed by stx-specific PCR-ELISA. Samples positive for stx were subsequently tested for the presence of wzy-O91, fliC-H21 and the adhesin-encoding gene saa. For minced meat, 16 (2·2%) and 11 (1·5%) samples were found positive for (stx, wzy-O91, fliC-H21) and (stx, wzy-O91, fliC-H21, saa) combinations, respectively. For raw milk, seven (3·4%) samples were found positive for the (stx, wzy-O91, fliC-H21) combination but none of these contained saa. Two STEC O91:H21 saa-positive strains and three STEC O91 H21– and saa-negative strains were isolated by colony hybridization. Conclusions:  A low prevalence of potentially pathogenic STEC O91:H21 in food products was found using a combination of PCR assays targeting stx, wzy-O91, fliC-H21 and saa. Significance and Impact of the Study:  The PCR-based approach described here represents a valuable method for rapid screening of food samples contaminated by STEC O91:H21.