EFFECT OF DIET ON THE SHEDDING OF ESCHERICHIA-COLI O157-H7 IN A SHEEPMODEL

The purpose of this study was to develop a sheep model to investigate reproduction, transmission, and shedding of Escherichia coli O157:H7 i n 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 se lective-enrichment protocol that detected E. coli O157:H7 at levels as low as 0.06 CFU per g of ovine feces was developed, Horizontal transm ission of infection occurred between the lambs and most of the nondose d mothers. When animals were kept in confinement and given alfalfa pel let feed, lambs receiving the higher dose shed the bacteria sooner and longer than all other animals. However, when the animals were release d onto a sagebrush-bunchgrass range, every animal, regardless of its p revious status (dosed at one of the inoculum levels tested or nondosed ) shed E. coli O157:H7 uniformly. Shedding persisted for 15 days, afte r which all animals tested negative. E. coli O157:H7 reproduction and transmission and the combined effect of diet change and feed withholdi ng were also investigated in a pilot study with experimentally inocula ted rams. Withholding feed induced animals to shed the bacteria either by triggering growth of E. coil O157:H7 present in the intestines or by increasing susceptibility to infection. Introduction of a dietary c hange with brief starvation caused uniform shedding and clearance of E . coli O157:H7, and all animals then tested negative for the bacteria. This work suggests that appropriate preharvest management to control diet may significantly reduce the risk of E. coli O157:H7-positive ani mals going to slaughter.