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Title: Assessing the risk of leafy green vegetables as a transmision pathway of verocytotoxigenic Escherichia coli to consumers
Author: Merget, Bernhard
ISNI:       0000 0004 6498 0861
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2017
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Verocytotoxigenic Escherichia coli (VTEC) is a major cause of diarrheal infections. It is increasingly associated with the consumption of fresh produce and responsible for several international outbreaks with severe sequelae. Quantitative risk assessment (QRA) aim to evaluate the risk of contamination, quantify uncertainties and identify potential mitigation steps. Current published QRA focus on post-harvest process steps without consideration of pre-harvest factors. This study aimed to identify preharvest knowledge gaps and quantify the potential for growth of VTEC in plant tissue prior to harvest. Risk factors were used to develop a QRA for VTEC O157:H7 in ready-to-eat (RTE) salad from farm-to-fork. Plant host metabolites were analysed by mass spectrometry and chromatography. Further plant and bacteria derived factors involved in pre-harvest colonisation were determined and implemented into a QRA. The burden of disease was estimated as the probability of illness by consuming RTE salad in the United Kingdom (UK). VTEC was shown to frequently internalise into lettuce and spinach to high concentrations. There, it can persist, evade surface decontamination and crosscontaminate equipment and produce during processing. The probability of illness was estimated to be 2.66 * 10-5 for lettuce and 1.51 * 10-5 for spinach. Internalisation was determined as the driving factor for 1820 illnesses per year in the UK associated with the consumption of lettuce and 950 with spinach, respectively. Mitigation steps had limited impact on internalised VTEC O157:H7 and mostly reduced external bacteria. Outputs from the QRA indicate the insufficiency of current mitigation steps to reduce internal VTEC O157:H7 and highlights the need for advanced decontamination procedures. The QRA tool can be used for the development of industrial guidelines in order to improve food safety in the UK and Europe.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Escherichia coli infections ; Salad greens ; Risk assessment