Jan. 1, 2012 - Feb. 28, 2014Award Number
Jitu Patel, Ph.D.
USDA - ARS
Manan Sharma, Ph.D.Resources
There have been a series of produce-related outbreaks involving E. coli O157:H7 and Salmonella in the last 20 years. It is critical to have produce free from pathogens as most produce is consumed raw or minimally processed. Good Agricultural Practices and Good Manufacturing practices at the preharvest and postharvest settings, respectively, have been implemented in recent years to minimize pathogen contamination. However, even occasional transfer of pathogens to fresh produce during preharvest can result in outbreaks, necessitating massive produce recalls. This project proposes to evaluate the role of cover crop systems in reducing the risk of pathogens in the pre-harvest environment; specifically, glucosinolate-derived compounds from Brassica spp. as a green manure to control E. coli O157:H7 and Salmonella in soil. Broccoli will be grown in high tunnels and after harvest of florets, remnant crops will be tilled over in the soil. The persistence of E. coli and Salmonella strains inoculated in soil will be monitored over a period of time. Results will determine the efficacy of green manure as intervention to control enteric pathogens in soil and on fresh produce.
The number of foodborne outbreaks linked to fresh produce has increased in last decades. Increased consumption of fresh produce, better outbreak surveillance system, and changes in production and distribution of fresh produce have contributed to this increased trend. Trace back investigations in many of these outbreaks have identified contamination at the farm level. Preharvest sources of contamination include contaminated manure, manure compost, irrigation water, wild and domestic animals, and other indirect sources such as birds and insects. As a major source of nutrients for crop productions, soil and soil amendments play vital role in safety of fresh produce. Contaminated or inadequately composted manure may transfer pathogens in soil. This proposed study uses a green manure from Brassica plants to control enteric pathogens in soil. The glucosinolate (GSL)-derived compounds, natural antimicrobials of certain Brassica plants, will be used to reduce attenuated strains of enteric pathogens in soil. In this proposed study, we will evaluate the antimicrobial activity of several GSL-derived compounds against E. coli O157:H7 and Salmonella strains in vitro (Objective 1). At least 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 in further studies (Objective 2). For objective 3, we will inoculate soil with attenuated green fluorescent protein (gfp) -expressing strains of Escherichia coli O157:H7 and Salmonella and till over 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 (n = 240) 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. For objective 4, Spinach will be grown in control and green manure-fertilized soil using standard agricultural practices. Spinach plant tissues will be sampled every week for up to 8 weeks for potential transfer of pathogen from soil. The results from this study will provide practical method for biocontrol of enteric pathogens in soil, thereby reducing potential produce-associated outbreak or massive produce recall. The antimicrobial effect of green manure on non-pathogenic surrogate strains will be also investigated at the farm level, contingent upon grower’s support and commitment. This proposal will address the identified research priorities (1.1) of “Compost, Soil Amendment Fertilizer Use and Cultivation Practices”.