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Title: The immune response in cattle to virulence factors of enterohaemorrhagic Escherichia coli
Author: Gibbs, Richard
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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E. coli 0157:H7 causes serious human disease including haemolytic uraemic syndrome and haemorrhagic colitis. Cattle are a known reservoir for E. coli 0157:H7, but despite often-large levels of carriage, appear unaffected by the organism. Two important factors in the ability of E. coli 0157 to cause disease are i) the possession of a 35Kbp pathogenicity island known as the locus of enterocyte effacement (LEE) and ii) the production of verotoxin. The products of the LEE interact bringing about intimate attachment to gut eneterocytes via the formation of attaching and effacing (AE) lesions. The role of the bovine intestinal microbiota and immune system in protection against E. coli 0157 associated disease is unclear. PCR and monoclonal antibodies were used to compare the distribution of the five E. coli LPS core types (R1-R4 + K12) within two populations of faecal isolates from healthy humans and cattle. To study the immune response in cattle LPS antigens were prepared and recombinant Intimin280 and EspB were cloned into the pGEX-4t2 expression vector. The GST tagged proteins were purified by affinity chromatography. ELISA and immunoblot were used to examine the sera of healthy and experimentally infected cattle for antibodies reactive to antigens from E. coli 0157:H7. E. coli possessing R1 core LPS were most frequently detected in both human and cattle populations (50% and 40% respectively). Compared to the human isolates a significantly higher level of bacteria with R3 core LPS was detected among the bovine commensal E. coli (p < 0.05). In each population the highest level of antibody detected was reactive to the R4 core. In cattle the level of anti- R3 core antibody was significantly higher than the level of anti-R1, R2 and K12 antibody (p < 0.01). This was not observed in humans. Healthy adult cattle were found to have little or no antibody reactive to Int280. Prior to experimental challenge with E. coli 0157, a number of calves had little or no detectable antibody to either Int280 or EspB; all other calves had detectable levels. The period of experimental infection did not alter the level of response in these animals. LPS was the only antigen found to elicit a response in any of the calves. The ability of the E. coli 0157 inoculum to colonise the calves appeared unaffected by the levels of anti-lnt280, EspB and LPS antibody detected. The antibodies present in the sera of the experimentally infected calves did not prevent the formation of AE lesions on HeLa cell monolayers Antibody detected in calves prior to experimental infection may have been acquired from colostrum. However the lack of systemic responses to Int280 observed in healthy adult cattle would suggest that the response detected in calves originates from exposure to these antigens at birth. It is possible that the maturation of the commensal flora and local mucosal immunity in the calf reduces the level of systemic exposure to antigens such as Int280 and EspB and as a result the systemic response diminishes. Despite the presence of antibodies reactive to Int280, EspB and LPS, E. coli 0157 is still able to colonise calves yet disease is not recognised. The role of the bovine immune system in protection against E. coli 0157 disease remains unclear.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available