Investigation into the colonisation and excretion of Escherichia coli O157 in cattle

Brett Stone (2010). Investigation into the colonisation and excretion of Escherichia coli O157 in cattle MPhil Thesis, Veterinary Science and Animal Production, The University of Queensland.

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Author Brett Stone
Thesis Title Investigation into the colonisation and excretion of Escherichia coli O157 in cattle
School, Centre or Institute Veterinary Science and Animal Production
Institution The University of Queensland
Publication date 2010-10
Thesis type MPhil Thesis
Supervisor Dr Ian Wilkie
Total pages 129
Total colour pages 18
Total black and white pages 111
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary ABSTRACT This study involved the microscopic examination of the bovine rectoanal junction (RAJ) collected from a total of 62 slaughter cattle at an abattoir in South East Queensland, Australia. These tissues were examined via an immunohistochemical technique, initially developed as part of this study, for visual confirmation and evaluation of E. coli O157 colonisation and specific histopathological criteria were also evaluated to determine if microscopic changes were present within the RAJ mucosa as a result of E. coli O157 colonisation. Microbial culture results (performed by Dr. Narelle Fegan, Food Science Australia, Cannon Hill) were also obtained from these and other animals with culture results then compared with those obtained via microscopy. In the first instance, this was performed as a double-blinded study whereby bacterial culture and microscopic examination were performed independently without knowledge of the results obtained by other detection methods. Attaching and effacing (A/E) lesions were not observed along the RAJ mucosa of any of the cattle sampled, regardless of colonisation status and level of faecal E. coli O157 excretion. There was no significant difference in the numbers of lymphocytes, neutrophils, plasma cells or eosinophils within the RAJ mucosa between colonised and non colonised cattle indicating that E. coli O157 colonisation of the bovine RAJ does not induce a host inflammatory response. Random sampling of a group of cattle presenting for slaughter revealed an overall prevalence of E. coli O157 culture positive animals of 10%. In this group of cattle, and in another group of cattle with a known positive shedding status, a single high shedding animal was present with this animal being responsible for over 99% of the E. coli O157 shedding within each group. The presence of one of these animals was associated with a prevalence of 30% culture-positive cattle within the batch of animals sampled on that particular visit. The immunohistochemical technique developed and utilised in this study was highly specific for E. coli O157 with no cross-reaction with either of E. coli O26:H11 (EC 473), E. coli O111:H- (EC26) and E. coli O91:H21 (EC21) serotypes. Utilising an E. coli O157-spiked agar gel, it was estimated that this technique allowed for the visual detection of E. coli O157 bacteria at a minimum concentration of approximately 3.85 x 103 bacteria/ml. Mucosal-associated bacterial colonies were only observed in one animal, with this animal also shedding the largest faecal concentration of E. coli O157 (4.6 x 105 CFU/g faeces) of all cattle within the study. Colonisation of this animal was multifocal rather than diffuse, a total of only 14 bacterial colonies were observed and no colonies were observed in regions immediately overlying mucosal-associated lymphoid follicles. All bacterial colonies were adherent to enterocytes in regions heavily concentrated with submucosal lymphoid follicles, and the number of bacteria per colony varied between 1 and 40.
Keyword E. coli O157, cattle, intestinal, colonisation, recto-anal-junction, immunofluorescence
Additional Notes Colour Page Numbers: 57, 62, 67, 68, 69, 70, 74, 80, 87, 88, 89, 93, 95, 98, 99, 100, 101, 102.

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Created: Tue, 09 Nov 2010, 20:28:48 EST by Mr Brett Stone on behalf of Library - Information Access Service