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Submitted to: UJNR Food & Agricultural Panel Proceedings
Publication Type: Proceedings Publication Acceptance Date: 10/2/2015 Publication Date: 11/15/2015 Citation: Patel, J.R. 2015. Brassica vegetables as a green manure to control Escherichia coli O157:H12 in soil. UJNR Food & Agricultural Panel Proceedings. Proceedings of the U.S. and Japan Cooperative Program in Natural Resources. p.47-49. Interpretive Summary: Foodborne illnesses associated with consumption of fresh produce have increased in recent years. In many cases, fresh produce contamination occurs at the farm level via soil or irrigation water. We investigated the role of glucosinolate-hydrolyzed compounds (GHC) from broccoli to control E. coli O157:H12 in soil. The GHC content of broccoli varied with cultivar and its fraction. E. coli O157:H12 populations were significantly reduced in soil when broccoli remnants were tilled into the soil following harvest. The bacterial reduction was rapid when soil was treated with benzyl isothiocyanate, one of the GHC compounds. This is the first report on role of Brassica vegetables to control enteric pathogens in soil. This information should be of interest to other scientists and to the produce industry. Technical Abstract: Plant remnants tilled over in soil after harvest of Brassica crops may possess antimicrobial from exudates secreted in soil following residual incorporation. We investigated the role of broccoli remnants tilled over after harvest for reducing enteric pathogens in soil. The glucosinolate-hydrolyzed compounds (GHC) obtained commercially were evaluated for their antibacterial activity using a disc diffusion assay on tryptic soy agar (TSA). Salmonella were more sensitive to these compounds than E. coli O157:H7 or non-pathogenic E. coli. Benzyl isothiocyanate (BIT) exhibited a significantly higher zone of inhibition than other antimicrobials or Gentamicin (positive control) against Salmonella strains. Three broccoli cultivars: Arcadia, Belstar, and Diplomat were grown in a greenhouse to determine their glucosinolate (GSL) content by high performance liquid chromatography - mass spectrometry (HPLC- MS). The GSL of broccoli varied with cultivar and its fraction; glucotrapaeolin content was up to 10x higher in roots of the Diplomat cultivar than in roots of Arcadia or Belstar. Broccoli (Pacman cultivar) grown at Beltsville farm was tilled over after harvest and soil was spray-inoculated with E. coli O157:H12 strain (7 log CFU/ml) followed by additional treatment of glucosinolate or plant antimicrobials. E. coli O157:H12 populations in BIT-treated soil were not detected by direct plating after 7 days, whereas populations ranged from 0.9 to 2.0 Log CFU/g of soil treated with other antimicrobials. The field study repeated with five broccoli cultivars (Arcadia, Diplomat, Green Magic, Belstar, and Imperial) revealed differences in the E. coli O157:H12 persistence with type of broccoli cultivars tilled over in soil. E. coli O157:H12 were undetectable after 12 weeks in soil tilled over with Green magic and Imperial broccoli cultivars. The results shows that the tilling over of the broccoli remnants as a green manure after harvest as well as GDC has the potential in reducing E. coli O157:H12 populations in soil. |
