1a. Objectives (from AD-416):
The overall objective of this study is to assess the persistence and transfer of norovirus, Salmonella, Escherichia coli O157:H7 and avian pathogenic E. coli (APEC) on leafy greens and basil to gain information to better enhance the safety of produce and to reduce transmission of these pathogens in the field onto leafy greens. Technion-Israel will use basil and spinach as the food vectors of study for persistence and mechanisms of attachment of Salmonella, while the University of Delaware and USDA-EMFSL in Beltsville, will evaluate lettuce, spinach and basil in their studies of norovirus and bacteria. The University of Delaware will investigate persistence of noroviruses, APEC and nonpathogenic E. coli on plant surfaces in a comparison study, while USDA-EMFSL will evaluate E. coli O157:H7, APEC, nonpathogenic E. coli, and Salmonella simulating field conditions using lower, more realistic population levels and different irrigation regimes.
1b. Approach (from AD-416):
Objective 1. University of Delaware: To investigate the persistence of norovirus on lettuce, spinach and basil with viral detection and counting by plaque assay and RT-PCR, and to determine the sites of adherence on produce using confocal microscropy. Objective 2. Technion–Israel: To determine the effect of the irrigation regime on transfer and survival of Salmonella in plants; irrigation methods that will be investigated: Dripping vs. spraying, day vs. night, summer vs. wintercrops, daily vs. multiple short irrigation. Objective 3. USDA EMFSL: To determine the fate of enterohemorrhagic, avian pathogenic, non-pathogenic E. Coli, and Salmonella introduced to leafy green foliar surfaces in irrigation water at levels stated in the California Leafy Green Marketing Agreement.
3. Progress Report:
Leafy greens have been shown to be susceptible to contamination with pathogenic E. coli resulting in human illness. Avian pathogenic E. coli (APEC) could be an unrecognized source of human illness from produce contamination, and could contaminate produce crops through poultry manure applied to agricultural fields. This study assessed the survival of avian pathogenic E. coli on lettuce and spinach, and compared the survival of APEC to E. coli O157:H7 and E. coli O104:H4 – both known human pathogens – on basil. Results show that APEC survived as long or longer than E. coli O157:H7 on all three plants evaluated. These results show that APEC can survive on leafy green commodities like other pathogenic E. coli, and should be considered a potential source of contamination of fresh produce. A peer-reviewed manuscript published in the Journal of Zoonoses and Public Health resulted from this work.
Markland, S., Shortlidge, K., Hoover, D., Yaron, S., Patel, J.R., Singh, A., Sharma, M., Kniel, K. 2012. Survival of pathogenic Escherichia coli on basil, lettuce, and spinach. Zoonoses and Public Health. DOI: 10.1111/zph.12033.