1a. Objectives (from AD-416):
ARS is interested in the role of pre-harvest sources of contaminations to fresh produce. The Cooperator is interested in improving the microbial safety of fresh produce.
1b. Approach (from AD-416):
Soil (soil amendments, compost) and irrigation water are major sources of pre-harvest contamination of fresh produce. We will utilize plant natural defense mechanism (glucosinolate-derived compounds) as a green manure to control attenuated strains of enteric pathogens in soil. Brassica plants will be grown in hoop houses. After crop harvest, remnant plant tissues will be tilled over as a green manure. Soil inoculated with attenuated strains will be sampled periodically for their persistence in presence of green manure.
3. Progress Report:
The natural antimicrobials found in Brassica plants may reduce enteric pathogens in soil, thereby reducing potential transfer of pathogens on fresh produce. The antimicrobial effects of green manure (broccoli remnants tilled under) and other glucosinolate derived compounds (GDC) were evaluated at the farm level for their ability to control E. coli O157:H12. After harvest of broccoli florets (Packman cultivar), broccoli remants were tilled into the soil and the soil was sprayed with E. coli O157:H12. Additional soil plots were treated with GDC following E. coli O157:H12 inoculation. Soil samples were analyzed for surviving populations of E. coli O157:H12 for up to 84 days after treatment. In general, populations of E. coli O157:H12 decreased in soil with time irrespective of treatment. E. coli O157:H12 populations in benzyl isothiocyanate (BIT)-treated soil were not detected by direct plating after 7 days, whereas in other treatments populations ranged from 10 to 100 bacteria per gram of soil. E. coli O157:H12 were recovered only in control untreated soils after 28 days; populations were below the detection limit in all treated soil (one organism per gram). These results reveal that the tilling under of broccoli remnants as a green manure after harvest, and the application of GDC and natural plant volatiles, have the potential to significantly reduce E. coli O157:H12 populations in soil.