Purpose: This study determined the range of counts of pSTEC serotypes O157, O26, and O111 in the feces of beef cattle at slaughter, which were previously deemed positive for pSTEC and assessed whether a relationship existed between pathogen counts and production systems or animal attributes.
Methods: The pSTEC counts were determined for cattle fecal samples (n=111) using a combined most probable number and real-time PCR approach. Analysis was conducted by comparing animal class (veal, dairy, and beef), carcass weight, plant processing volume, or production system (grass, grain, and dairy) with the frequency of counts, which fell into a range that was either greater or less than a single log MPN g-1 value. The values used were one, two, three, four, and five log MPN g-1. Comparisons were performed in contingency tables using chi-squared or Fisher’s exact tests and relationships were deemed significant if P<0.01.
Results: Counts of pSTEC ranged from <-0.52 to 6.89 log MPN g-1 feces. At a P value of <0.01, the only association observed was in production systems where pSTEC counts of <one log MPN g-1 were more frequent in grass-fed (62.5% of 48) than in grain-fed animals (7.7% of 13). The study found no evidence of a relationship between the frequency of count (at any given log range) and animal class, carcass weight, or plant processing volume.
Significance: Previous studies suggest that an increased risk of pathogen transmission during processing is most likely to occur when the concentration of pSTEC exceed three log cfu g-1 feces. At this threshold, none of the factors investigated would indicate an increased risk of carcass contamination during processing.