Molecular characterization of Escherichia coli O157H7 hide contamination routes - feedlot to harvest

Abstract

This study was conducted to identify the origin of Escherichia coli O157:H7 contamination on steer hides at the time of harvest by sampling the feedlot, transport trailers, packing plant holding pens, and colons of feedlot steers in conjunction with the hides. A total of 50 positive hide samples were collected in two geographical locations: the Midwest (n = 25 positive hides) and Southwest (n = 25 positive hides). At the feedlot, sample locations included: water troughs, pen floors, feed bunks, and loading chutes. Transport trailer samples were obtained from the inner walls and floors of trailers. At the packing plant, the following samples were collected: packing plant holding pen floors, side rails, drinking water, and restrainer boxes. Hide samples were screened and confirmed for presence of E. coli O157:H7. When at least one hide sample tested positive for E. coli O157:H7, all corresponding companion samples were screened and confirmed for presence of E. coli O157:H7. Identification of E. coli O157:H7 isolates was conducted by fingerprinting all positive samples using Pulsed Field Gel Electrophoresis after digestion with Xanthomonas badrii (XbaI). Furthermore, isolates were analyzed using multiplex Polymerase Chain Reaction for the known E. coli O157:H7 gene markers: stx1, stx2, eaeA, and hlyA. Feedlot water troughs, pen floors, feed bunks, loading chutes; truck trailer side walls, floors; packing plant holding pen floors, side rails, and packing plant cattle drinking water samples tested positive for presence of E. coli O157:H7. Data was analyzed by stratifying isolates by gene markers present and by packing plant using Pulsed Field Gel Electrophoresis. Isolates that had greater than 7 differences in banding patterns were not considered to be related. In this study hide samples were traced to other hide, colon, feedlot pen floor fecal, packing plant holding pen drinking water, and transport trailer side wall samples. Links were determined between packing plant side rails, feedlot loading chutes and feedlot pens; and between truck trailer, different feedlots, and colons of multiple cattle. The current study is the first to identify genotypic matches between transport side walls and cattle hide samples within the packing plant.