Prevalence of Escherichia coli O157:H7 from cull dairy cows in New York state and comparison of culture methods used during preharvest food safety investigations.

A number of protocols for the cultural detection of Escherichia coli O157:H7 in clinical fecal specimens have been proposed. In the present study direct plating of cattle feces was compared to three different broth enrichment protocols, i.e., a protocol with modified E. coli broth with novobiocin, a protocol with Trypticase soy broth with cefixime and vancomycin, and a protocol with Gram-Negative Broth with novobiocin, for their relative abilities to detect E. coli O157:H7 in feces. In all enrichment protocols, dilutions of the enrichment broths onto 150-mm sorbitol-MacConkey agar plates to which cefixime and tellurite were added were used along with reading of agar plates at both 24 and 48 h. Fecal samples came from a preharvest food safety project in which feces from New York cull dairy cattle from a northeastern packing plant along with experimentally inoculated adult dairy cow feces were tested. The performances of the broth enrichments were comparable to each other, but the broth enrichments were superior to direct plating in their ability to detect E. coli O157:H7. Regardless of the culture protocol used, recovery of E. coli O157:H7 is more likely from fresh fecal specimens than from frozen samples. An overall prevalence of E. coli O157:H7 fecal shedding by New York cull dairy cattle of 1.3% was found in specimens just before processing at the packing plant.