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Rapid sample preparation method for PCR-based detection of Escherichia coli O157:H7 in ground beef
S Cui1, C M Schroeder, D Y Zhang
1Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA. jm332@umail.umd.edu
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 103 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.