Fecal Escherichia coli O157 : H7 shedding patterns of orally inoculated calves

To assess the duration of fecal shedding upon initial infection, the durati on of shedding after subsequent re-infection and the effects of dietary res triction and antibiotic treatment on shedding recrudescence, four, one-week -old calves were orally inoculated on three separate occasions with 5 x 10( 8) cfu of Escherichia coli O157:H7 strain 86-24 Nal-R. Fecal shedding was f ollowed by serial culture three times weekly. Following the first inoculati on, the calves shed E. coli O157:H7 in their feces for a mean of 30 days, w ith a range of 20 to 43 days. Following the second and third inoculations, the calves shed E. coli O157:H7 in their feces for 3-8 days. In each of the three inoculations, feed was withheld from the calves for 24 h after they had become fecal culture negative. Two calves resumed shedding, one for 1 d ay and the other for 4 days, after food was withheld after the third inocul ation, but not in the first two inoculations. In the third inoculation, one calf resumed shedding for one day after treatment with oxytetracycline. No E. coli O157:H7 strain 86-24 Nal-R was found in the calves at necropsy, Th ese calves did not exhibit persistent low-level shedding, and did not appea r to be persistently colonized with E. coli O157:H7. (C) 1999 Elsevier Scie nce B.V. All rights reserved.