Purpose: The antimicrobial activity of GHP against Salmonella and Escherichia coli O157:H7 was evaluated. A field study was conducted to evaluate the ability of GHP and broccoli residues to control E. coli O157:H12 in organic soil.
Methods: Isothiocyantes (benzyl-, butyl-, ethyl-, isopropyl-, methyl-, phenethyl-, allyl-), Indole methyl oxazolidinone, and methyl propyl pyrazole carboxylic acid were evaluated for antibacterial activity using a disc diffusion assay on Tryptic soy agar (TSA). Five strains of Salmonella or E. coli O157:H7 were individually spread-plated on TSA (50 µL, 6 log CFU/ml) and 6-mm sterile filter disk impregnated with 15 µL GHP was overlaid. Following 24 h incubation at 37°C, zone of inhibition was measured. Broccoli florets and Benzyl isothiocynate (BIT, 0.013%) was incorporated in soil inoculated with E. coli O157:H12 (5.5 log CFU/g) and raked for uniform dispersion. Surviving E. coli O157:H12 populations in treated soil (n=90) were determined for 98 days by spiral plating on CT-SMAC NA and by 3-tube MPN procedure.
Results: BIT (10 mg/ml) exhibited significantly higher zone of inhibition than other GHPs or gentamicin (positive control) against Salmonella strains. Salmonella Negev was the most sensitive serovar to BIT. The antibacterial effects of BIT and other GHPs against E. coli O157:H7 were comparable to gentamicin. BIT treatment reduced E. coli O157:H12 by 3 log CFU (P < 0.05) in 14 days. The E. coli O157:H12 were undetectable (< 0.4 log CFU/g) after 56 days in BIT- and broccoli-treated soil.
Significance: Current study demonstrates Brassicaceae family crops can be used as a green manure to control enteric pathogens in soil contaminated with compost or irrigation water.