| dc.description.abstract | The pathogens enterohemorrhagic Escherichia coli (EHEC), Salmonella enterica, and Listeria monocytogenes are prominent causes of foodborne illness. If they reach the pre- or post-harvest environment of produce, they can survive for extended periods of time and transfer to post-harvest processing to reach consumers. There are a multitude of factors that influence this survival, bacterial attachment, and isolation, which have been identified for pre- and post-harvest conditions. However, how these pathogens respond to the changes in these systems requires more work to inform effective control methods.
To compare the efficacy of an isolation method in different types of matrices, we used immunomagnetic separation (IMS) to selectively isolate strains of EHEC representing non-O157 serogroups from feces, ground beef, and lettuce. The differing matrices and the presence of native microbes seemed to interrupt isolation, with O111 and O145 beads performing the poorest. To understand how EHEC attachment is influenced by food processing-relevant conditions, we investigated the effects of PBS, 4.5% NaCl, and lettuce exudates on attachment to stainless steel (SS). These simulated limited nutrients, osmotic pressure, and alternative carbon sources that EHEC can encounter during food processing. Initial association to SS was reduced under the 4.5% NaCl for all EHEC strains, but this did not translate to reduced attachment. Variation in attachment was observed in lettuce exudates only, and this variation was driven by strains.
Finally, we evaluated pathogen survival in the pre-harvest environment. We simulated an aqueous environment that EHEC, Salmonella, and L. monocytogenes might encounter during pre-harvest. Soils were collected from distinctly different environments and extracts were created by leeching water-soluble components from soil. Extracts were inoculated with pathogens and they were monitored to see if the varying chemistries or microbiomes influenced survival. Initially, survival was reduced in the low-nutrient extract, particularly when native microbes were present. Overall, work done here identified factors like matrix or specific environmental conditions and their effects on the isolation, attachment, and survival. These data provide the basis for further work to improve accuracy of IMS-based detection in complex matrices, determine strain-specific mechanisms for EHEC attachment, and assess associations between soil microbiome composition and pathogen survival. | en_US |
