PCR-BASED DETECTION OF VEROTOXIN-PRODUCING ESCHERICHIA-COLI (VTEC) IN-GROUND BEEF

Pathogenic strains of Escherichia coli producing verotoxins (VTs) have been recognized as a cause of human disease, and rapid and sensitive detection tests are urgently needed to ensure the safety of food, espe cially ground beef. We applied two nested polymerase chain reaction (P CR) assays to detect the genes encoding VT1 and VT2 irrespective of th e bacterial serotype, In combination with a direct sample preparation protocol, we were able to uncover the presence of about 110 CFU of ver otoxinogenic E. coli (VTEC) in 10 g of ground beef. When a six-hour en richment was included, we found the detection limit to be in the range of 1 to 10 bacterial cells per 10 g of ground beef. To evaluate our d etection system, we tested 30 ground beef samples originating from but cher shops in Berne, Switzerland. One sample yielded positive PCR resu lts for both the VT1 and VT2 genes, indicating the presence of verotox inogenic E. coli. Finally, 20 food homogenates, shown to contain E. co li strains by standard culture, were analysed with our method, and the gene encoding VT2 was detected in one cheese sample. The results sugg est that the described PCR method can serve as a valuable tool for the surveillance of VTEC contamination of foods.