Determine the length of time of E. coli O157:H7 survival on the hide of living cattle. Explore factors affecting E. coli O157:H7 survival on cattle hides.
Approach: Cattle from multiple pens at the MARC feedlot will be screened for colonization by E. coli O157:H7. Animals from pens with a high prevalence of E. coli O157:H7 will be randomly sorted into two groups. One group will stay in the feedlot while the other group will be isolated in individual pens. The hides and feces of both groups will be periodically sampled to determine the presence of E. coli O157:H7. In the individual pens, recontamination of the hides by fecal matter will be minimized by treating the animals with Neomycin and by frequent cleaning of the pens. No such measures will be taken in the feedlot. E. coli O157:H7 isolates will be genotyped using pulsed field gel electrophoresis. Sample collection. Hide samples will be obtained using Speci-Sponges (Nasco, Fort Atkinson, WI) moistened with 20 ml of buffered peptone water (BPW, Difco Laboratories, Becton Dickinson Microbiology Systems, Sparks, MD). Sponges will be wrung out in the bag, then removed from the bag and used to swab the hide or carcass. The hide sample will be collected from a 1000-cm2 area over the flank. Ten grams of feces will be obtained from rectal grab and placed into a filtered stomacher bag. Sample processing. Sponge bags will be massaged thoroughly and 80 ml of tryptic soy broth will be added. To the fecal samples will be added 90 ml of TSB-phosphate. All samples will be incubated at 25 deg C for 2 h, 42 deg C for 6 h, and then held at 4 deg C overnight. E. coli O157 detection. All sample bags will be subjected to immuno-magnetic separation and plated onto ctSMAC and ntChromagar. After the plates are incubated, up to three suspect colonies will be picked and tested by latex agglutination (DrySpot E. coli O157; Oxoid, Basingstoke, England).