Glucosinolate-derived Compounds as a Green Manure for Controlling Escherichia coli O157:H7 and Salmonella in Soil
Environmental Microbial and Food Safety Laboratory
2013 Annual Report
1a.Objectives (from AD-416):
The objective is to determine the glucosinolates content of different cultivars of broccoli grown in greenhouses, and investigate the persistence of enteric pathogens (surrogate strains) in soil tilled over with green manure (remnant crop after broccoli harvest) containing GSL-derived compounds.
1b.Approach (from AD-416):
To determine the antimicrobial activity of glucosinolate (GSL)-derived compounds in vitro against enteric pathogens. Five cultivars of broccoli will be grown in high tunnels and after harvest crop remnants will be analyzed for GSL-derived compounds. The cultivar with the greatest antimicrobial activity which is also economically feasible to growers will be used to investigate the persistence of pathogens in soil tilled over with green manure containing GSL-derived compounds. After the broccoli harvest, soil will be inoculated with attenuated green fluorescent protein (gfp) -expressing strains of Escherichia coli O157:H7 and Salmonella and tilled over with broccoli crop remnants as a green manure in soil. Soil devoid of green manure but inoculated with Escherichia coli O157:H7 and Salmonella will serve as control. Samples from control and green-manure treated soils will be collected weekly for 12 weeks and analyzed for surviving populations of enteric pathogens E. coli O157:H7 and Salmonella using molecular assays and Confocal microscopy. The results from this study will provide a practical method for biocontrol of enteric pathogens in soil, thereby reducing potential produce-associated outbreak or massive produce recall.
The antimicrobial effects of green manure (Brassica plant remnants tilled under) and other glucosinolate derived compounds (GDC) were evaluated at the farm level for their ability to control E. coli O157:H12 in soil. Four Broccoli cultivars (Arcadia, Bellstar, Diplomat, and Green Magic) grown in a high tunnel were harvested at maturity, broccoli remants were tilled into the soil, and the soil was sprayed with E. coli O157:H12. Soil samples are being analyzed for surviving populations of E. coli O157:H12 (ongoing project). Preliminary results revealed antimicrobial activity of green manure against E. coli O157:H12 in soil. The reduction in E. coli O157:H7 populations (10-500 bacteria per gram) were not significantly different due to the effects of broccoli cultivar.