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Survival and virulence of the zoonotic pathogens Salmonella and E. coli O157 in greenhouse cultivation of butterhead lettuce (SALCOSLA)

Main research question/goal
Zoonotic pathogens (human disease causing microorganisms transmitted through animals) can be transferred to vegetables. If they occur on raw or minimally processed vegetables (IVth gamma), they can pose a risk for human health, as illustrated by a number of recent outbreaks associated with these food products. This study focuses on leafy vegetables, specifically butterhead lettuce, which we use as a model. In this project, we ask: To which extent are the most obvious contamination sources for zoonotic pathogens in glasshouse cultivation (seed and irrigation water) responsible for the occurrence of these pathogens on the plant? How do Salmonella and E. coli O157 survive and behave on or in the plant? To which extent should we advise screening for zoonotic pathogens in seed and/or seedlings and irrigation water along with the standard screening for plant quarantine organisms and plant pathogens?
Research approach
ILVO investigates two clearly documented contamination sources (seed/seedlings and irrigation water) which can reach the upper plant parts. We investigate the survival and spread of zoonotic pathogens from seed to the sprouting seeds and the survival in irrigation water with various organic loads. Later, we observe the behaviour and the human virulence of Salmonella and E. coli O157 on butterhead lettuce in light of different factors (growth stage, pathogenic strain, epiphytic versus endophytic contact, lesions). The diverse external conditions present in practice are incorporated into the experimental setup. We carry out artificial contaminations with Salmonella and E. coli O157 with natural virulent strains as well as with avirulent strains for biosafety reasons. The avirulent strains are used for inoculation experiments of whole plants in the phytotron as well as to investigate the effect of natural virulence of these pathogens on the behaviour on plants as habitat with detached leaf assays. Further, we make use of bioluminescent lux-labeled mutants to trace the localization in the plant parts.
The aim of this project is to reveal the conditions in which Salmonella and E. coli O157 can occur and survive on butterhead lettuce. It elucidates contamination sources such as seed and irrigation water. We can thus better estimate the food safety risk related to zoonotic pathogens on lettuce. Furthermore, based on these data we can advise whether screening for zoonotic pathogens in seed and/or seedlings and irrigation water is necessary.
External partner(s)
Ugent - Fac. Bio-ingenieurswetenschappen
Date:1 Apr 2009 →  31 Mar 2013