Survival of S. Enterica and E. Coli O157:H7 in Soil and Internalization into Leafy Greens as Affected by the Presence of Biochar and Fungi

Non-Technical Summary:<br/>
The U.S. leafy green market is annually valued at over $2 billion and leafy greens have been considered the "riskiest food regulated by the FDA" (by the Center for Science in the Public Interest) with a total of 363 foodborne outbreaks involving 13,568 illnesses, primarily due to Salmonella and pathogenic E. coli. Ongoing research conducted at the USDA, ARS in Wyndmoor, PA has determined that naturally symbiotic arbuscular mycorrhizal fungi as well as biochar byproducts from the production of fast pyrolysis biofuel, when added to crop soil, may affect the survival and internalization of Salmonella and E. coli O157:H7 into Romaine lettuce roots and stems. This research project will investigate the influence of biochar and arbuscular mycorrhizal fungi on survival of Salmonella, E. coli O157:H7 and other shiga toxin-producing E. coli (STEC) in soil and internalization into leafy greens.
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Approach:<br/>
The approach designed to execute the three objectives of this research project are as follows: (I) The influence of varying levels of biochar on the survival of Salmonella and E. coli O157:H7 in crop soil under varying climate-controlled conditions will be determined. Variables include 4 biochars added to soil at 4 amendment levels (0, 1, 3, and 5%). Soil will be inoculated with E. coli O157:H7 or Salmonella enterica. Soil moisture will be adjusted to 2 final levels (3 and 15%), representing low and medium moistures and sampled for up to 6 months. Next, (II) the influence of the arbuscular mycorrhizal fungus (AMF) Glomus intraradices on internalization and survival of Salmonella and E. coli O157:H7 in leafy greens, in scaled-up conditions will be assessed. Romaine lettuce will be cultivated with or without AMF and inoculated. Plant roots, shoots and soil will be sampled weekly for 8 weeks. Finally, (III) the effects of AMF x biochar on reducing the survival of Salmonella and E. coli O157:H7 in soil and internalization and survival in leafy greens will be evaluated. These experiments will include (1) Two of the best biochar soil amendments, (2) added at one amendment level, (3) inoculated with one pathogen (4) with and without AMF. Root, shoot and soil will be microbiologically sampled up to week 8 and plant growth measured via plant height, live weight and dry weight, to determine interactions between biochar and plant growth.