Ruminant reservoirs and invertebratevectors for transfer of human pathogens to vegetable crops and ready-to-eat foods

Abstract

This was a study to determine if invertebrate vectors (i.e. flies and slugs) were able to acquire human pathogens from local ruminant faeces and potentially transfer them to vegetables or ready-to-eat food. A field survey revealed that slugs are able to acquire pathogenic strains of E. coli O.157 that were indistinguishable from those isolated from local sheep faeces. Laboratory experiments demonstrated that commensal E. coli had relatively long survival rates on and in slugs, where the slugs were able to transfer E. coli by direct contact or excretion. Escherichia coli had a slow decline rate in excreted slug faeces with a decimal reduction time of 13.9 days. The results suggest that slugs have the potential to transfer pathogenic E. coli to vegetables. The second part of this work aimed at identifying temporal or host related relationships in the Campylobacter population of cattle and sheep. The Multi-locus sequence typing (MLST) technique was used in addition to quantifying the prevalence and concentrations of Campylobacter excreted by cattle and sheep present on the same farm. Statistically significant temporal variations were identified in addition to differences between the two hosts. During the faecal sampling, flies were also collected. Flies were found to carry identical sequence types (STs) to those present in local ruminant faecal samples. However, despite the relatively low Campylobacter prevalence in flies, certain STs were over represented, suggesting some degree of host restriction. A low number of slugs were also sampled where the Campylobacter ST isolated, had not been identified on this farm or elsewhere. Flies and slugs are able to acquire E. coli O157 and Campylobacter strains, thus posing a potential risk of transfer to vegetable crops.EThOS - Electronic Theses Online ServiceGBUnited Kingdo