Effect of diet on the shedding of Escherichia coli O157:H7 in a sheep model.

The purpose of this study was to develop a sheep model to investigate reproduction, transmission, and shedding of Escherichia coli O157:H7 in ruminants. In addition, we investigated the effect of diet change on these parameters. Six groups of twin lambs given oral inoculations of 10(5) or 10(9) CFU of E. coli O157:H7 and their nondosed mothers were monitored for colonization by culture of fecal samples. A modified selective-enrichment protocol that detected E. coli O157:H7 at levels as low as 0.06 CFU per g of ovine feces was developed. Horizontal transmission of infection occurred between the lambs and most of the nondosed mothers. When animals were kept in confinement and given alfalfa pellet feed, lambs receiving the higher dose shed the bacteria sooner and longer than all other animals. However, when the animals were released onto a sagebrush-bunchgrass range, every animal, regardless of its previous status (dosed at one of the inoculum levels tested or nondosed) shed E. coli O157:H7 uniformly. Shedding persisted for 15 days, after which all animals tested negative. E. coli O157:H7 reproduction and transmission and the combined effect of diet change and feed withholding were also investigated in a pilot study with experimentally inoculated rams. Withholding feed induced animals to shed the bacteria either by triggering growth of E. coli O157:H7 present in the intestines or by increasing susceptibility to infection. Introduction of a dietary change with brief starvation caused uniform shedding and clearance of E. coli O157:H7, and all animals then tested negative for the bacteria.(ABSTRACT TRUNCATED AT 250 WORDS)