Internalisation of Human Pathogens into Growing Salad Vegetables and Leafy Herb Salad

A previous BRIDGE-LINK (FQS 3) project identified the potential for Escherichia coli and Listeria monocytogenes to become internalised within growing spinach plants when introduced on the seed or hydroponic growth medium. Once internalised biocidal washing had a negligible impact on reducing their viability. This preliminary study used artificially high levels of human pathogens to inoculate seeds and hydroponic solution. The proposed work will build upon these studies to establish the risk of human pathogen uptake by growing salad vegetables when introduced in low numbers in the presence of an established competitive microflora. This will reflect the conditions expected to occur in the natural environment and hence provide a basis for determining the risk posed by human pathogens during plant propagation. The potential of human pathogens to become integrated into the internal (endophytic) populations of a diverse range of commercially important vegetable/leafy herb types will also be investigated. In addition, potential methodologies (seed decontamination and biocontrol agents) to minimise human pathogen internalisation will be evaluated on a laboratory and commercial scale.
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The main objectives of this project are:

<UL> <LI> Determine the influence of human pathogen numbers (range 102-103cfu/ml (g)) on the extent of internalisation into spinach when inoculated into hydroponic growth medium/soil microcosms.

<LI>Evaluate the role of competitive microflora in facilitating/minimising internalisation of human pathogens into growing spinach plants.

<LI>Survey different vegetables (crisp head type lettuce, celery, watercress, bean sprouts) and leafy herbs (parsley, coriander, basil) for the potential by which human pathogens can become internalised.

<LI>Evaluate the impact of soil properties (texture, pH, and organic matter) and plant cultivar on the internalisation of human pathogens.

<LI>Determine the impact of seed decontamination and biocontrol (biotization) measures in minimising the internalisation of human pathogens.