Experimental infection of calves and adult cattle with Escherichia coli O157:H7

Abstract

Preweaned calves and adult cattle were inoculated with 10 10 CFU of Escherichia coli O157:H7 strain 3081, a calf isolate which produces Shiga-like toxin, to define the magnitude and duration of fecal shedding of E. coli O157:H7 for each age group. Fecal samples of eight of eight, eight of eight, three of eight, and two of eight calves were positive at 2, 7, 14, and 20 weeks, respectively. In contrast, nine of nine, two of nine, and one of nine steers were positive at 2, 7, and 14 weeks, respectively. The magnitude of shedding (CFU per gram) by individual animals at any one time postinoculation varied widely within each age group but was greater for calves as a group. The differences in shedding patterns between adults and calves were statistically significant. After inoculation, 25 of 29 animals remained healthy and 4 of 17 calves had transient diarrhea. Histologic sections of the brain, kidney, jejunum, ileum, cecum, and colon taken at necropsy from nine calves either 3, 14, or 18 days postinoculation or three adults either 2, 3, or 4 days postinoculation were normal. E. coli O157:H7 was recovered from the alimentary tracts of all of the animals necropsied, and there was no evidence of spread to the liver, spleen, or kidneys. Four calves that had ceased shedding were reinfected when inoculated again with the same strain. E. coli O157:H7 was recovered from none of five and two of five adults inoculated with 10 4 and 10 7 CFU, respectively. If one assumes that the E. coli strain and cattle used in this study are representative of the larger populations encountered in the field, then these observations suggest the following conclusions. (i) Fecal shedding of toxigenic E. coli O157:H7 varies widely among animals of the same age group but persists longer in calves than in adults. (ii) E. coli O157:H7 does not spread from the alimentary tract to other organs. (iii) Previous infection does not prevent reinfection by the same strain of E. coli O157:H7. (iv) The infectious dose of in vitro-grown E. coli O157:H7 for normal adult cattle is high (>10 4 and probably Ն10 7 CFU). (v) Most cattle infected with E. coli O157:H7 remain clinically normal.

Attaching-effacing Bacteria in Animals

“…Only some of these putative AEEC strains are demonstrably pathogenic, suggesting that the maintenance of the LEE in the wider E. coli population confers a survival advantage. One AEEC strain, the human pathogen EHEC O157:H7, is normally non-pathogenic but persists in a proportion of cattle and sheep (Cray and Moon, 1995;Kudva et al, 1995;Cornick et al, 2000;Wray et al, 2000;Conedera et al, 2001;Cookson et al, 2002a), pigs and possibly other non-human species. The LEEmediated capacity of E coli O157:H7 to adhere to epithelial cells may play a role in its persistence in animals (Gyles, 1998).…”

Attaching-effacing Escherichia coli Infections in Cattle

“…In the second study, 54 A/E lesions were demonstrated in 3-and 5-month-old experimentally infected calves, and the same 12-month-old naturally infected steer as the one reported previously. 53 The identification of the terminal rectum as the principal site for EHEC O157:H7 bacterial colonization and A/E lesion formation may explain why, with few exceptions, 51,55-57 these lesions were not detected in intestinal tissue in studies involving 5-day-old gnotobiotic 58 or conventional neonates and young (2-8-week-old) calves, [59][60][61] or cattle older than this infected with EHEC O157:H7. 60 In only one other study 51 had rectal tissue from an older (in this case 3-4-month-old) inoculated animal been examined, and in only one study had tissue from the rectum from adult cattle been shown to be susceptible to E coli O157:H7induced A/E lesions; and this was in explants, not live animals.…”

“…53 The identification of the terminal rectum as the principal site for EHEC O157:H7 bacterial colonization and A/E lesion formation may explain why, with few exceptions, 51,55-57 these lesions were not detected in intestinal tissue in studies involving 5-day-old gnotobiotic 58 or conventional neonates and young (2-8-week-old) calves, [59][60][61] or cattle older than this infected with EHEC O157:H7. 60 In only one other study 51 had rectal tissue from an older (in this case 3-4-month-old) inoculated animal been examined, and in only one study had tissue from the rectum from adult cattle been shown to be susceptible to E coli O157:H7induced A/E lesions; and this was in explants, not live animals. 55 Hence, the studies by Naylor and colleagues 53,54 were the first to show A/E lesions in a live, naturally infected adult (12-month-old) bovine, and first to show they were limited to the terminal rectum.…”

“…These findings are consistent with the results of previous experimental inoculation studies. 60,61 Other studies have demonstrated that small intestinal (ileal) tissue of conventional calves older than neonates is susceptible to A/E lesions with E coli O157:H7 when inoculated into ligated loops. The age of the calves in most of these studies ranged from 28 to 38 days 57,62,63 ; however, as noted previously, ligated ileal loops of conventional neonatal (2-to 6-day-old) calves 44 also support these lesions.…”

Clinical signs, reproduction of attaching/effacing lesions, and enterocyte invasion after oral inoculation of an O118 enterohaemorrhagic in neonatal calves

“…Coexistence between EPEC/EHEC strains and other diarrhoeagenic agents has already been noticed in field studies and may be related to the severity and persistance of diarrhoea in farms [5]. The age of the animal is also important: with strains of serotypes O157:H7 and O26:H11 clinical signs could not be reproduced in calves aged one to two weeks but could be reproduced well in newborn calves [1,6,7,18]. The opposite situation may exist for strains belonging to other serotypes, mimicking the situation of EPEC in rabbits [21,26].…”