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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: Persistence of enterohemorrhagic and non-pathogenic E. coli on spinach leaves and in rhizosphere

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

Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 5, 2008
Publication Date: August 3, 2008
Citation: Patel, J.R., Millner, P.D., Nou, X., Sharma, M. 2008. Persistence of enterohemorrhagic and non-pathogenic E. coli on spinach leaves and in rhizosphere [abstract]. International Association for Food Protection Program and Abstract Book. P1-06. p. 54.

Technical Abstract: Introduction: Outbreaks associated with leafy greens have focused attention on the persistence of Escherichia coli O157:H7 on produce. Ecological interactions of E. coli O157:H7 and spinach require detailed characterization. Purpose: Survival of E. coli O157:H7 and non-pathogenic E. coli was evaluated on spinach plants and in organic soil in a growth chamber. Methods: Five separate inocula, each containing one strain of E. coli O157:H7 and one non-pathogenic E. coli isolate (from plants or soil), were grown in water extracts of dairy manure solids. Spinach cultivar ‘Whale’ was grown in sandy loam soil (3 percent organic matter). Leaf and soil inocula consisted of: 100uL in 5uL droplets on the upper side of leaves and 1mL in soil used to inoculate individual 4-week old plants with 6.5 log CFU/plant and 7.5 log CFU/200 g soil per plant. Four replicates of each plant shoot and soil sample per inoculum were analyzed on day 0 and weekly for 28 days for E. coli O157:H7 and non-pathogenic E. coli (by MPN), and for heterotrophic plate counts (HPC). Results: E. coli O157:H7 was not detected on plant shoots after 7 days but did survive in soil for up to 28 days. Non-pathogenic E. coli survived up to 14 days on shoots, and at low levels for up to 28 days. MPN assay was more sensitive in detecting target organisms than spiral plating. HPCs in soil at day 7 were significantly greater than those at day 0, but populations on day 0 and day 28 in soil and on plants were similar (P>0.05). Significance: Populations of E. coli O157:H7 survived for a shorter duration on spinach shoots than in soil. Non-pathogenic E. coli were detected intermittently on spinach up to 28 d. Results suggest survival of these E. coli O157:H7 and non-pathogenic strains were similar on leaves and in rhizosphere soil.

Last Modified: 10/21/2014
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