Evaluation of 5′ nuclease based detection assays to detect Escherichia coli O157:H7 from food products

Two 5' nuclease-based PCR methods (PCR-LS-50B and PCR-7200) were evaluated to determine their sensitivity for detecting Escherichia, coli O157.H7 from pure cultures and in food samples enriched in different media and after different incubation periods. The PCR-7200 method was able to detect E. coli O157:H7 at greater than or equal to 10(2) CFU/mL in pure culture in both mECB and EEB. In spiked meat samples, the PCR-7200 procedure was capable of detecting the eaeA gene at lower concentrations than the PCR-LS-50B procedure, regardless of the meat type or enrichment medium. Escherichia coli O157:H7 spiked at 0.3 CFU/mL was detectable after 9 h in EEB, but it was not detected in mECB within 24 h. An enrichment time of 4 h in mECB was needed to detect E. coli O157:H7 when spiked at higher levels (41 CFU/mL). ne detection levels reported in this study are similar with other reported PCR-based detection techniques for E. coli O157:H7, however, the 5' nuclease-based assays are less labor intensive and capable of higher sample throughput because of their automated detection and analysis steps.