Evaluation of a Novel Phage Protein Ligand Method with Immunomagnetic Separation and PCR GENE-UP® to Detect and Isolate the Top 7 Shiga-Toxin-Producing Escherichia coli (STEC) Serogroups in Meat and Raw Milk Cheeses

Introduction: Shiga toxin-producing Escherichia coli (STEC) are an important cause of foodborne illness. This pathogen can be responsible for gastrointestinal diseases ranging from diarrhea to haemorrhagic colitis and haemolytic uremic syndrome. As a result, the food industry needs fast, sensitive, and complete methods for STEC detection to ensure a safe food supply.

Purpose:  A comprehensive method, combining immune concentration (IC) and PCR, has been developed to detect and isolate the top 7 STEC (O157, O26, O103, O111, O145, O45 and O121) in foods at risk. The performance of this method was evaluated with the ISO 13136 horizontal method, in artificially inoculated foods.

Methods:   This method included two steps: automated IC with VIDAS^® ESPT prior to the GENE-UP PCR assays for stx, eae, and serogroup markers. If there are positive results for these markers, another IC is used to isolate presumptive colonies on specific plates agar. A total of 40 STEC strains were inoculated onto 22 different meats and raw milk cheeses. For test method evaluation, the sample size was 375g meat or 25g cheese. For the ISO 13136 horizontal method, the sample size was 25g for both matrices.

Results:  A total of 110 food enrichment were tested. The results obtained for both methods are comparable under the experimental conditions described.

Significance:   This study has demonstrated that the VIDAS ESPT combined with the GENE-UP PCR is a promising tool for screening and isolating STEC strains from food enrichments. This automated method will provide technical improvement and time savings in routine testing for the food industry.