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Title: Using the agricultural environment to select better surrogates for foodborne pathogens associated with fresh produce

Author
item Cook, Kimberly - Kim
item GIVAN, ETHAN - Western Kentucky University
item MAYTON, HOLLY - University Of California
item Parekh, Rohan
item TAYLOR, RITCHIE - Western Kentucky University
item WALKER, SHARON - University Of California

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2017
Publication Date: 9/27/2017
Citation: Cook, K.L., Givan, E., Mayton, H., Parekh, R.R., Taylor, R., Walker, S. 2017. Using the agricultural environment to select better surrogates for foodborne pathogens associated with fresh produce. International Journal of Food Microbiology. 262/80-88. doi: 10.1016/j.ijfoodmicro.2017.09.017.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2017.09.017

Interpretive Summary: Despite the best efforts of industry and regulatory agencies to identify and implement good agricultural practices (GAPs) that eliminate pathogen contamination, significant produce associated outbreaks continue to occur. Nonpathogenic surrogate bacteria can be used in place of for common produce-associated foodborne pathogens to develop better produce production and processing methods. The objective of this study was to to identify environmental Escherichia coli (E. coli) isolates (N=63) from manures (poultry, swine and dairy) and surface water sources which have biological properties that are similar to those of the produce associated foodborne pathogens E. coli O157:H7 and Salmonella. In general, selected environmental E. coli isolates were non-pathogenic serotypes that lacked virulence genes and exhibited cell surface characteristics (zeta potential, hydrophobicity and exopolysaccharide composition) that were within 15% of values for S. Typhimurium. E. coli O157:H7 and the E. coli QC strain behaved similarly; both were in the lowest 10% of isolates for biofilm formation and leaf attachment. In contrast, the environmental E. coli isolates and S. Typhimurium formed more biofilm when grown in lettuce lysates and surrogates attached to lettuce in a manner similar to Salmonella (p< 0.05). These data suggest that the environment may provide a valuable resource for selection of superior bacterial surrogates to mimic the behavior of some foodborne pathogens.

Technical Abstract: Despite the best efforts of industry and regulatory agencies to identify and implement good agricultural practices (GAPs) that eliminate pathogen contamination, significant produce associated outbreaks continue to occur. Identification of nonpathogenic surrogates for common produce-associated foodborne pathogens will facilitate efforts to develop better GAPs and produce processing strategies. The objective of this study was to use a tiered process to identify environmental Escherichia coli (E. coli) isolates (N=63) from manures (poultry, swine and dairy) and surface water sources which have genotypic (phylotype, virulence, adhesion and biofilm genes) and phenotypic (biofilm formation, growth rate, lettuce adhesion and cell surface properties) properties similar to those of the produce associated foodborne pathogens E. coli O157:H7 and Salmonella enterica serotype Typhimurium (S. Typhimurium). In general, selected environmental E. coli isolates were non-pathogenic serotypes that lacked virulence genes and exhibited cell surface characteristics (zeta potential, hydrophobicity and exopolysaccharide composition) that were within 15% of values for S. Typhimurium. The E. coli isolates from manures and surface waters formed biofilms more often when grown in low nutrient media prepared from lettuce lysates (23.8%) than when grown on high nutrient broth (7.14%) and attached to lettuce to a greater extent than did a commonly used E. coli quality control strain (p< 0.05). S. Typhimurium formed nine times more biofilm when grown on lettuce lysates (OD546 1.222 ± 0.405) than when grown on high nutrient broth (OD546 0.133 ± 0.191). E. coli O157:H7 and the E. coli QC strain behaved similarly; both were in the lowest 10% of isolates for biofilm formation and leaf attachment. In contrast, the environmental E. coli isolates and S. Typhimurium formed more biofilm when grown in lettuce lysates and surrogates attached to lettuce in a manner similar to Salmonella (p< 0.05). These data suggest that the environment may provide a valuable resource for selection of superior bacterial surrogates for some foodborne pathogens.