Progress 10/01/12 to 09/30/13
Outputs
Progress Report 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. 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. 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.
Impacts
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Progress 10/01/11 to 09/30/12
Outputs
Progress Report 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. 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. Antibacterial activity of GDC, mainly, isothiocyanates, indole methyl oxazolidinone, and methyl propyl pyrazole carboxylic acid were evaluated against E. coli O157:H7 and its mutants deficient in surface appendages, nonpathogenic E. coli, and Salmonella. Sterile filter disc (6 mm) impregnated with 10-20 �L of GDC (10 mg/ml) were placed on Tryptic soy agar (TSA) plates seeded with respective bacteria. After 48 h incubation at 37�C, the diameter (mm) of the inhibitory zone around the disc was recorded. Antibacterial effect of GDC was dose-dependent, increasing with the dose applied. Salmonella were more sensitive to these compounds than E. coli O157:H7 or non-pathogenic E. coli. Benzyl isothiocyanate exhibited significantly higher zone of inhibition than other compounds or gentamicin (positive control) against Salmonella strains. The antibacterial effects of benzyl- and phenethyl isothiocyanate against E. coli O157:H7 were comparable to that of gentamicin. The antibacterial effect of 3-Methyl-1-propyl-1H-pyrazole-4-carboxylic acid and 1H-Indol-3- ylmethyl-2-oxazolidinone was not evident on test pathogens. A nonpathogenic E. coli O157:H12 strain enriched in bovine fecal slurry (7 log CFU/ml) was sprayed on five plots (5� x 4� plot, 1 L per plot). Plots were marked as (1) inoculated control (2) acetic acid (3) cinnamaldehyde (4) Sporan� and (5) BIT, and treated with respective antimicrobials. Soil samples were analyzed periodically for E. coli O157:H12 populations by spiral plating on MacConkey agar containing 50 mg/L nalidixic acid or MPN procedure. Populations of E. coli O157:H12 reduced in soil with time irrespective of antimicrobial treatment. BIT was superior to acetic acid, cinnamaldehyde, and Sporan� in reducing E. coli O157:H12 in soil. None of these compounds had any effect on native microorganisms of soil.
Impacts
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