2012 Annual Report
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.
Four different strains of avian pathogenic E. coli (APEC) were cultured in poultry manure was inoculated on 4-week-old Romaine lettuce plants simultaneously with a strain of E. coli O157:H7. Both strains showed similar survival patterns on Romaine lettuce, showing consistent survival and detection on Romaine lettuce plants up to day 8; after day survival of APEC and E. coli O157:H7 was sporadic until day 17. On 4-week old spinach plants, APEC and E. coli O157:H7 inoculum were inoculated at a lower level. Survival of APEC and E. coli O157:H7 on spinach plants was more consistent but at lower levels then on Romaine lettuce. Avian pathogenic E. coli seem to persist for longer durations that E. coli O157:H7 on lettuce but not on spinach.