Screening bovine carcass sponge samples for Escherichia coli O157 using a short enrichment coupled with immunomagnetic separation and a polymerase chain reaction-based (BAX) detection step

A bovine carcass sponge sample screening protocol for detecting Escherichia coli O157:H7 was composed of a short selective enrichment followed by an i mmunomagnetic separation (IMS) and target detection using the BAX E. coli O 157 polymerase chain reaction assay. This screening protocol was compared t o a culture-based method for detection of the organism in carcass sponge sa mples. Enriched samples were subjected to IMS; the bead suspension was divi ded and plated on selected media or stored at -20 degreesC, then subjected to BAX analysis. The results showed a high degree of agreement between the plating method and the BAX system. Fifty-two of the 59 culture-positive sam ples were also positive using the BAX system (88.1% sensitivity). Of the 76 samples that appeared negative for the presence of E. coli O157:H7 by the culture method, 66 were determined as negative using the BAX system (86.8% specificity). Four of the 10 samples found negative by the initial culture method and positive by the BAX method were subsequently found to be culture positive upon reanalysis. Based on these data, the BAX system combined wit h a short, selective enrichment and IMS may be a rapid, reliable, and simpl e method to screen for E. coli O157:H7 in carcass sponge samples. Our data indicate that optimization and subsequent testing of this protocol for use as a carcass screening tool are warranted.