Using the Agricultural Environment to Find Better Surrogates for Foodborne Pathogens.

Despite the best efforts of industry and regulatory agencies to identify and implement good agricultural practices (GAPs) to reduce or eliminate pathogen contamination, significant outbreaks associated with fresh produce continue to occur in the U.S. and around the world. Strains of E. coli isolated from livestock manure and water sources may be better surrogates of pathogens and contamination than are commonly used quality control and lab strains. In this study characteristics (biofilm and leaf attachment, carbon source utilization and cell surface) of environmental E. coli were compared to those of produce associated pathogens, E. coli O157:H7 and Salmonella typhimurium and a common quality control (QC) E. coli strain. Properties of the QC strain was found to be significantly different than than those  of Salmonella in both biofilm formation and leaf attachment (p < 0.05). Selected environmental surrogates formed greater biofilms when grown in lettuce lysates and attached to lettuce in a manner similar to Salmonella. In greenhouse scale experiments, it was found that all isolates persisted on lettuce leaves above detection levels for 22 days, but die-off rates were greater for the QC strain than those of the pathogens and selected surrogates (p < 0.05). Persistence of environmental isolates in soils (sandy loam and silt loam) with or without poultry litter amendments was affected by organic carbon content and was higher in silt loam soil than in sandy loam. In soils with no amendment, the surrogates and Salmonella persisted at levels above the detection limit (10³ cells/g) for at least 42 days. The data from this project provides support for the use of surrogates selected from the environment as improved representatives of produce associated human pathogens for agro-ecosystem settings.