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United States Department of Agriculture

Agricultural Research Service

Research Project: Improving the Safety and Post-Harvest Quality of Field Grown Organic Leafy Greens: Assessment of Good Agricultural/production Practices

Location: Environmental Microbial and Food Safety Laboratory

2013 Annual Report


1a.Objectives (from AD-416):
ARS EMFSL will focus on the objective to determine the factors influencing bacterial attachment to leafy greens surfaces and internalization of E. coli 0157:H7.


1b.Approach (from AD-416):
Foodborne outbreaks due to microbial contamination of fresh produce have been increasing in recent years. This proposal addresses methods to prevent, detect, monitor, control, and respond to potential food safety hazards in the production and processing of specialty crops, including fresh produce. The goals target identification of routes of introduction; factors that influence persistence and survival of E. coli and S. enterica in leafy greens and melons from production to finished product preparation; and dissemination of information across the nation. The results obtained during this study will help in developing alternative technologies to enhance the safety of produce and to educate/train different sectors of the produce industry and different groups of consumers on food safety practices to avoid consumption of contaminated produce. Ultimately, it will help specialty crop industries recover and retain consumer confidence and reduce food safety risks. For the proposed project, ARS, EMFSL, will focus on part of objective (1) to determine the factors influencing bacterial attachment to leafy greens surfaces and internalization of E. coli O157:H7 while the cooperator will conduct research to address part of objectives 1, 2 and 3-6.


3.Progress Report:

Shiga-toxigenic Escherichia coli O157:H7 (EHEC) outbreaks have been linked to consumption of fresh produce. Internalization of E. coli O157:H7 into organic leafy greens is of particular concern since these bacteria cannot be killed using standard disinfection methods. The internalization potential of E. coli O157:H7 into organic spinach roots and subsequent transfer to the edible portions of the plant was evaluated. The effects of curli (a bacterial surface appendage), spinach cultivar, and contamination level on EHEC internalization were also examined. Spinach cultivars Space and Waitiki were grown in soil and hydroponically under controlled conditions. After emergence of four true leaves, soil and hydroponic solutions were inoculated with EHEC strains. Spinach leaves, stems, and roots were sampled after 0, 7, 14, 21 and 35 days to determine the incidence and populations of internalized bacteria. EHEC internalized into hydroponically-grown spinach roots and dispersed to the stem and leaf. The internalization incidence was significantly affected by contamination level but not by curli expression or spinach cultivar. Further, internalization incidence was significantly greater (42.4%) in soil-grown spinach than in hydroponically grown spinach; probably due to extensive root damage in plants grown in soil. This study demonstrates that internalization is influenced by the contamination level and farming practices, necessitating pre-harvest interventions for controlling pathogens in composted manure and irrigation water.


Last Modified: 8/30/2014
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