Summary of Awards to Date

Rapid tests to specifically differentiate clinically significant from environmental STEC towards reducing unnecessary crop destruction

Date

Jan. 1, 2015 - Dec. 31, 2016

Funding Agency

University of California, Davis

Amount Awarded

$329,481.00

Investigator

Trevor Suslow, Ph.D.
University of California, Davis

Co-Investigator(s)

Michele Jay-Russell, Ph.D., University of California, Davis

Summary

Though exceptionally rare events, relative to the scale of production and consumption, there is ample evidence to know that produce samples sometimes contain pathogens of serious potential human health consequences. A group of bacterial pathogens, Shiga toxin‐producing E. coli (STEC) from diverse fresh produce were recovered from multi‐year sampling programs conducted by the UDSA, largely at wholesale distribution centers. Leafy greens, herbs, and specifically spinach were singled out for concern due to a STEC prevalence rate exceeding 50% of the total isolates recovered. Product testing is used by many but not all producers to pre‐screen leafy greens for bacterial pathogens, including STEC. Unfortunately, not all testing platforms rapidly distinguish STEC likely to cause human illness from those that lack the genetic traits necessary for infection. Due to the high perishability of these commodities, testing can lead to destruction of a field due to false association with dangerous STEC. The combined objectives of protecting consumers, reducing food waste, and improving sustainability can be enhanced by applying new advancements proposed in this research in specific detection of clinically relevant Shiga toxin‐ producing E. coli to risk management decisions and better defining the role of wildlife as vectors of preharvest contamination.

Technical Abstract

Though exceptionally rare events, relative to the scale of production and consumption, there is ample evidence to know that produce samples sometimes contain pathogens of serious potential human health consequences. After the E. coli O157:H7 outbreak on spinach in 2006, the programmatic testing of leafy greens at preharvest for raw commodity and fields intended for processing, incoming raw material, and/or finished packaged product greatly increased. A group of bacterial pathogens, Shiga toxin‐producing E. coli (STEC) from diverse fresh produce were recovered from multi‐year sampling programs conducted by the USDA, largely at wholesale distribution centers. Leafy greens, herbs, and specifically spinach were singled out for concern due to a STEC prevalence rate exceeding 50% of the total isolates recovered. Product testing is used by many but not all producers to pre‐screen leafy greens for bacterial pathogens, including STEC. Unfortunately, not all testing platforms rapidly distinguish STEC likely to cause human illness from those that lack the genetic traits necessary for infection. There has been a rapid expansion of platforms, kits, pathogen targets, and diversity of approaches to lot acceptance criteria. There has been a gradual but accelerating shift in product testing criteria and policies for the group of pathogens that includes EHEC and STEC. Some commercial kit test systems have been recently used that screen for the top‐seven EHEC (O157, O26, O45, O103, O111, O121, O145) based on the premise that these sub‐types are responsible for over 85% of clinical cases. However, due to the increasing recognition of diverse STEC in clinical cases, many commercial service labs have more recently been using detection and lot acceptance systems that employ the least diagnostic genetic markers for this group, presence of eae (intimin; attaching and effacing) and stx (either of two key forms of shigatoxin) in an enrichment culture. Presence of these two markers, alone or being contributed individually by independent cell lines, has resulted in frequent crop destruction involving many acres and substantial economic loss, at the individual grower level. Due to the high perishability of these commodities, testing can lead to destruction of a field due to false association with dangerous STEC. The combined objectives of protecting consumers, reducing food waste, and improving sustainability can be enhanced by applying new advancements proposed in this research in specific detection of clinically relevant Shiga toxin‐ producing E. coli to risk management decisions and better defining the role of wildlife as vectors of preharvest contamination. The anticipated outcome of this proposal is the development of a set of recommendations relative to rapid virulence profiling and its application to routine compliance and lot acceptance testing for fresh produce. This project is a starting point for a longer‐term effort to consolidate and clarify the available information on risk associated with the diverse STEC group and present this information in a guidance format that can help form industry‐based standards of practice. The outcomes would lead to both immediate transferable actions in pathogen testing protocols and serve as a first step towards fulfilling our collective responsibility to stewardship of the ag‐environment and associated regional landscape.