Meat Safety News Digests

Standard testing methods using stx, eae, and O serogroup–specific gene sequences for detecting the top six nonO157 STEC (i.e., O26, O103, O121, O111, O145, and O45) typically possess the disadvantage in which these genes may reside, independently, in different non-pathogenic organisms, leading to false-positive results. To this end, researchers from the U.S. explored the utility of the ecf operon as a single marker to detect eae-positive STEC from pure broth and primary meat enrichments. During the initial study, analysis of 501 E. coli isolates demonstrated a strong correlation (99.6%) between the presence of the ecf1 gene and the combined presence of stx and eae genes. Two subsequent studies were carried out to evaluate the potential use of an ecf1 detection assay to detect non-O157 STEC strains in enriched meat samples in comparison to the results using the U.S. Department of Agriculture Food Safety and Inspection Service (FSIS) method that detects stx and eae genes. It was evident in ground beef samples (n = 1,065) that the top six non-O157 STEC were detected in 4.0% of samples by an ecf1 detection assay and in 5.0% of samples by the stxand eae-based method. In contrast, in beef samples composed largely of trim (n = 1,097), the top six non-O157 STEC were detected at 1.1% by both methods. Estimation of false-positive rates among the top six non-O157 STEC revealed a lower rate using the ecf1 detection method (0.5%) than using the eae and stx screening method (1.1%). These results highlight that ecf1 detection assay has the potentials to be used as an alternative method for detection of nonO157 STEC to the standard methods.