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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Publications at this Location » Publication #253311
Title: Fate of Escherichia Coli 0157:H7 in field-inoculated lettuce.

Author
item MOYNE, ANNE-LAURE - University Of California
item Sudarshana, Mysore
item BLESSINGTON, TYANN - University Of California
item KOIKE, STEVEN - University Of California
item CAHN, MICHEL - University Of California
item HARRIS, LINDA - University Of California

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2011
Publication Date: 2/3/2011
Citation: Moyne, A., Sudarshana, M.R., Blessington, T., Koike, S.T., Cahn, M.D., Harris, L.J. 2011. Fate of Escherichia Coli 0157:H7 in field-inoculated lettuce. Food Microbiology. doi:10.1016/j.fm.2011.02.001.

Interpretive Summary: Irrigation methods were evaluated for impact on the persistence of attenuated Escherichia coli O157:H7 in the lettuce phyllosphere under field conditions throughout the production cycle. A split-plot design was used to evaluate the two main treatments - drip and overhead sprinkler irrigation - during four field trials conducted in the Salinas Valley, California between summer 2007 and fall 2009. Rifampicin-resistant attenuated E. coli O157:H7 ATCC 700728 (BLS1) was inoculated onto the soil beds after seeding or onto 2- or 4-week-old lettuce plants at a level of 7 log CFU ml-1. The bacterial population dynamics were monitored on the plants for 4 or 5 weeks after inoculation. When E. coli O157:H7 was inoculated onto 2-week old plants, the organism was recovered by enrichment in 1 of 120 or 0 of 240 plants at 21 or 28 days post inoculation, respectively. For all trials where inoculum was applied to 4-week old plants, the population size of E. coli O157:H7 declined by 2 to 5 log CFU/plant during the first 2 h to 2 days postinoculation, respectively. By day 7, counts were near or below the limit of detection (10 cells per plant) for 82% or more of the plants sampled. No significant difference (P > 0.05) in counts was observed between plants that were irrigated by drip or overhead sprinkler. The percent positive plants in the three trials declined to 4 to 28% 28 days postinoculation. Neither drip nor overhead sprinkler irrigation consistently influenced the survival of E. coli O157:H7 on lettuce.

Technical Abstract: Irrigation methods were evaluated for impact on the persistence of attenuated Escherichia coli O157:H7 in the lettuce phyllosphere under field conditions throughout the production cycle. A split-plot design was used to evaluate the two main treatments - drip and overhead sprinkler irrigation - during four field trials conducted in the Salinas Valley, California between summer 2007 and fall 2009. Rifampicin-resistant attenuated E. coli O157:H7 ATCC 700728 (BLS1) was inoculated onto the soil beds after seeding or onto 2- or 4-week-old lettuce plants at a level of 7 log CFU ml-1. The bacterial population dynamics were monitored on the plants for 4 or 5 weeks after inoculation. When E. coli O157:H7 was inoculated onto 2-week old plants, the organism was recovered by enrichment in 1 of 120 or 0 of 240 plants at 21 or 28 days post inoculation, respectively. For all trials where inoculum was applied to 4-week old plants, the population size of E. coli O157:H7 declined by 2 to 5 log CFU/plant during the first 2 h to 2 days postinoculation, respectively. By day 7, counts were near or below the limit of detection (10 cells per plant) for 82% or more of the plants sampled. No significant difference (P > 0.05) in counts was observed between plants that were irrigated by drip or overhead sprinkler. The percent positive plants in the three trials declined to 4 to 28% 28 days postinoculation. Neither drip nor overhead sprinkler irrigation consistently influenced the survival of E. coli O157:H7 on lettuce.