Rapid sample preparation method for PCR-based detection of Escherichia coli O157:H7 in ground beef

Aim: To develop an improved, rapid and sensitive sample preparation method for PCR-based detection of Escherichia coli O157:H7 in ground beef. Methods and Results: Fresh ground beef samples were experimentally inoculated with varying concentrations of E. coli O157:H7. PCR inhibitors were removed and bacterial cells were concentrated by filtration and centrifugation, and lysed using enzymatic digestion and successive freeze/thaw cycles. DNA was purified and concentrated via phenol/chloroform extraction and the Shiga toxin 1 gene (stx1) was amplified using PCR to evaluate the sample preparation method. Without prior enrichment of cells in broth media, the detection limit was 10(3) CFU g(-1) beef. When a 6 h enrichment step was incorporated, the detection limit was 1 CFU g(-1) beef. The total time required from beginning to end of the procedure was 12 h. Conclusions: The sample preparation method developed here enabled substantially improved sensitivity in the PCR-based detection of E. coli O157:H7 in ground beef, as compared to previous reports. Significance and Impact of the Study: Superb sensitivity, coupled with quick turn-around time, relative ease of use and cost-effectiveness, makes this a useful method for detecting E. coli O157:H7 in ground beef.