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Escherichia coli Contamination of Lettuce Grown in Soils Amended with Animal Slurry

Jensen, Annette Nygaard; Storm, Christina; Forslund, Anita; Baggesen, Dorte Lau and Dalsgaard, Anders (2013) Escherichia coli Contamination of Lettuce Grown in Soils Amended with Animal Slurry. Journal of Food Protection, 76 (7), pp. 1137-1144.

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A pilot study was conducted to assess the transfer of Escherichia coli from animal slurry fertilizer to lettuce, with E. coli serving as an indicator of fecal contamination and as an indicator for potential bacterial enteric pathogens. Animal slurry was applied as fertilizer to three Danish agricultural fields prior to the planting of lettuce seedlings. At harvest, leaves (25 g) of 10 lettuce heads were pooled into one sample unit (n ~ 147). Soil samples (100 g) were collected from one field before slurry application and four times during the growth period (n ~ 75). E. coli was enumerated in slurry, soil, and lettuce on 3M Petrifilm Select E. coli Count Plates containing 16 mg/liter streptomycin, 16 mg/liter ampicillin, or no antimicrobial agent. Selected E. coli isolates (n ~ 83 originating from the slurry, soil, and lettuce were genotyped by pulsed-field gel electrophoresis (PFGE) to determine the similarity of isolates. The slurry applied to the fields contained 3.0 to 4.5 log CFU/g E. coli. E. coli was found in 36 to 54% of the lettuce samples, streptomycin-resistant E. coli was found in 10.0 to 18.0% of the lettuce samples, and ampicillinresistant E. coli in 0 to 2.0% of the lettuce samples (the detection limit was 1 log CFU/g). The concentration of E. coli exceeded 2 log CFU/g in 19.0% of the lettuce samples. No E. coli was detected in the soil before the slurry was applied, but after, E. coli was present until the last sampling day (harvest), when 10 of 15 soil samples contained E. coli. A relatively higher frequency of E. coli in lettuce compared with the soil samples at harvest suggests environmental sources of fecal contamination, e.g., wildlife. The higher frequency was supported by the finding of 21 different PFGE types among the E. coli isolates, with only a few common PFGE types between slurry, soil, and lettuce. The frequent finding of fecal-contaminated lettuce indicates that human pathogens such as Salmonella and Campylobacter can be present and represent food safety hazards.

EPrint Type:Journal paper
Type of presentation:Speech
Keywords:Organic lettuce, manure, E. coli contamination
Subjects: Food systems > Food security, food quality and human health
Crop husbandry > Composting and manuring
Crop husbandry
Crop husbandry > Crop health, quality, protection
Research affiliation: Denmark > DTU - Technical University of Denmark
European Union > CORE Organic > PathOrganic
Denmark > KU - University of Copenhagen
Deposited By: Jensen, Ms Annette Nygaard
ID Code:23106
Deposited On:09 Aug 2013 08:46
Last Modified:09 Aug 2013 08:46
Document Language:English
Refereed:Peer-reviewed and accepted

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