Review of the Food-borne Zoonoses Research ... - ARCHIVE: Defra

Abstract of research
Projects OZ0706, OZ0710 and OZ0713 have run over the past ten years with VLA as the
lead organisation within a highly collaborative network involving numerous partners,
notably Bristol University and the Moredun, and more recently with the Defra Fellowship
at Edinburgh University, the IAH and Imperial College. The overall goal was to
understand the mechanisms of colonisation and persistence of Escherichia coli O157:H7
in sheep (the second most prevalent affected species) and other at risk food producing
animals. It is not possible to summarise these three highly successful projects within 250
words as the studies generated 40 peer reviewed papers (see section 9) to which the
reader has access, as all are in the public domain.
Various O157 strains have been used in deliberate oral inoculation studies in
conventionally reared ovines, porcines, caprines and poultry. All these animals are
susceptible to persistent colonisation.
In ovines, very young animals (six days old) are susceptible to colonisation by O157 by
intimate attachment as AE lesions were observed in the large intestine, although very
rare and very small. In older animals (six weeks and six months old) O157 induced
lesions were exceedingly rare and were only seen in the caecum. However, intimin
deficient mutants were cleared more quickly than wild type strains and interestingly a tir
mutant was cleared even more rapidly in the same models. These findings confirmed
persistent colonisation is dependent upon intimin and translocation of the Tir into host
cells.
In caprines, conventionally reared goats aged 6 days are susceptible to colonisation by
O157 by intimate attachment as AE lesions were observed ileum, caecum, colon and
rectum from all animals. Eight-week-old conventionally-reared goats were inoculated
orally in separate experiments with O157:H7 and an intimin deficient derivative.
Significantly fewer initimin deficient bacteria were shed only on days 2 (p=0.003) and 4
(p=0.014) whereas from day 7 to 29 days there were no differences. Tissues taken from
this study group were examined histologically. AE lesions were not observed at any
intestinal site of the animals except for one animal, which uniquely shed approximately, 1
x 10 7 O157:H7 per gram of faeces for the preceding three days and which showed a
heavy, diffuse infection with cryptosporidia and abundant, multifocal AE lesions in the
distal colon, rectum and at the terminal rectum and recto-anal junction. These AE lesions
were confirmed by immunohistochemistry to be associated with E. coli O157:H7. We
conclude that co-infection may be predisposing factor for colonization in caprines (and
therefore probably other at risk species). Five-year-old nannies with kids at foot were
dosed orally with O157:H7 at about six days after parturition. Faecal shedding was
variable up to day 11 after dosing (~1 x 10 4 E. coli O157:H7 cfu per gram faeces) but no
kids became positive for E. coli O157:H7 organisms. Thus, sucking kids are refractive to
colonisation by E. coli O157:H7 probably because the challenge dose was low and the
kids had access to milk that is known to be highly protective.
In porcines, we showed intimin was not required for persistence although in neonates AE
lesions were observed readily after oral inoculation. Indeed, intimin deficient mutants
adhered equally well to IPI-21 (porcine) cells and IVOC (all sections of the gut) as the
wild type. Also, histological analysis of pig tissues at post mortem examination revealed
that E. coli O157 specifically stained bacteria were associated with the mucosa of the
ascending and spiral colon but no AE lesions were detected.
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