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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL ECOLOGY AND SAFETY OF FRESH ON-FARM ORGANICALLY GROWN PRODUCE Title: Effect of green manure on E. coli O157:H7 survival in soil

Authors
item Patel, Jitu
item Nou, Xiangwu
item Millner, Patricia
item Sharma, Manan

Submitted to: United States-Japan Cooperative Program in Natural Resources
Publication Type: Proceedings
Publication Acceptance Date: September 25, 2008
Publication Date: September 30, 2008
Citation: Patel, J.R., Nou, X., Millner, P.D., Sharma, M. 2008. Effect of green manure on E. coli O157:H7 survival in soil. Proceedings of the United States-Japan Cooperative Program in Natural Resources. p. 72-73.

Interpretive Summary: Green manure is the remnants of crops that remain in the field after harvest, and are plowed back into the field to increase fertility. The application of green manure at the field level is practical because it reduces the waste at processing facilities and lowers transportation costs from the field. Green manure may also add nutrients to the soil for the next planting of crops. We evaluated role of green manure (cabbage, spinach, and daicon) for their effects on the survival of E. coli O157:H7 in soil from pre-harvest environments. A cocktail of four E. coli 0157:H7 strains was inoculated in cassettes containing green biomass. The cassettes were embedded in a pot containing soil and green biomass manure. Cassettes were sampled every week for up to 5 weeks and analyzed for E. coli O157:H7 populations using Most Probable Number (MPN) procedure. Survival of E. coli O157:H7 in soil varied with strain as well as inoculation method. E. coli O157:H7 ISEH strain was the most sensitive and RM4406 was the most resistant strain to green manure. Cabbage, a brassicaceous green manure significantly reduced E. coli O157:H7 in soil. While E. coli O157:H7 populations in soils decrease with time, they were still detectable after 35 days. These results have particular relevance to organic production in that they indicate that green manures can effect pathogen survival.

Technical Abstract: Green manure is the remnants of crops (stems, outer leaves, tops of leaves, etc.) that remain in the field after harvest, and are plowed back into the field to increase fertility. The role of green manure in the survival of E. coli O157:H7 in soil has not been examined. We evaluated three types of green manure: cabbage, spinach, and daicon for their effects on the survival of E. coli O157:H7 in soil from pre-harvest environments. A cocktail of four E. coli 0157:H7 strains [Kanamycin resistant USDA3055, Kanamycin resistant ISEH carrying chromosomal green fluorescent protein (GFP), ampicillin resistant B6914 carrying plasmid GFP, and nalidixic acid resistant RM4406] was inoculated in soil by two methods; animal manure pellets (solid) and exudates of animal manure on spinach leaves (liquid). Bacterial inoculation was carried out in cassettes which contained 10 g of damp soil on the bottom and ca. 2 g relevant biomass. A cassette was closed, labeled accordingly, and placed in the pot containing soil and chopped green biomass manure. Cassettes were sampled every week for up to 5 weeks and analyzed for E. coli O157:H7 populations using MPN procedure. Overall E. coli O157:H7 MPN (3 log cfu/g) detected with cabbage manure at 35 days were significantly lower (P<0.05) than the E. coli O157:H7 populations detected in control (3.63 cfu/g), spinach (3.78 cfu/g), and daikon (4.22 cfu/g) manures. Survival of E. coli O157:H7 in soil varied with strain as well as inoculation method. E. coli O157:H7 ISEH strain was the most sensitive and RM4406 was the most resistant strain to green manure. After 35 days, E. coli O157:H7 strains USDA3055 and ISEH recovered from cabbage manure were significantly lower than those recovered from daikon or spinach manure. While E. coli O157:H7 populations in soils decrease with time, they are still detectable after 35 days. Cabbage, a brassicaceous green manure significantly reduces E. coli O157:H7 in soil.

Last Modified: 8/30/2014
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