Escherichia coli O157:H7-persistence studies in experimentally infected chickens and pigs

Escherichia coli O157:H7, first implicated in human illness in 1982, is an emerging food borne pathogen currently accounting for 74,000 cases of illness in the United States which manifests itself as diarrhea illness, hemorrhagic colitis and in extreme cases hemolytic uremic syndrome, a severe complication of the disease seen in approximately 10% of infections which can lead to death. Beef products are most often implicated as sources for infections and studies have found carriage rates up to 28% for normal healthy cattle, with herd prevalence from 22-100%. Although several ruminant species have been implicated in outbreaks of illness, the role of other food production animals in the spread of the disease is unclear. Included here are experimental studies conducted to determine the ability of chickens and pigs to become persistently infected with E. coli O157:H7 and the possibility of these animals becoming potential reservoirs. Broiler chickens and feeder pigs were inoculated with five E. coli strains. The inoculum included two Shigatoxigenic E. coli (STEC) O157:H7 strains, two enterotoxigenic E. coli (ETEC) strains and one enteropathogenic E. coli (EPEC) strain. A high dose inoculum with all five strains at approximately 1010 cfu/animal and a low dose inoculum with the STEC strains at approximately 107 cfu/animal and the EPEC and ETEC strains remaining at approximately 1010 cfu/animal were used. All of the strains persisted in the feces of some chickens given the high dose inoculum at two weeks post inoculation (pi). However, none of the strains persisted in the alimentary tracts of chickens at two months. In contrast to the results with chickens, the STEC strains persisted in the alimentary tracts of some pigs at two months pi following inoculation with both the high and low dose inocula. When all strains were given at approximately 1010 cfu (high dose inoculum) the STEC strains persisted in greater numbers and in more pigs than did the other strains. The results of this study demonstrated that persistent ([Greater than or equal to symbol]2 months) E. coli O157:H7 infections can occur in pigs. These findings were similar to those reported from sheep inoculated with the same set of E. coli strains