Ecology and risk assessment of E. coli O157:H7 and Salmonella typhimurium in the primary production chain of lettuce

E. Franz

Research output: Thesisinternal PhD, WU

Abstract

Survival of the green fluorescent protein-transformed human pathogens Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium was studied in a laboratorysimulated lettuce production chain. Dairy cows were fed 3 different roughage types: high digestible grass silage + maize silage (6:4), low digestible grass silage and straw. Each was adjusted with supplemental concentrates to a high and low crude protein level. The pathogens were added to manure which was subsequently mixed (after 56 and 28 d for resp. E. coli O157:H7 and Salmonella serovar Typhimurium) with 2 pairs of organically and conventionally managed loamy and sandy soil. After another 14 d, iceberg-lettuce seedlings were planted and checked for pathogens after 21 d of growth. Survival data were fitted to a logistic decline function (exponential for E. coli O157: H7 in soil). Roughage type significantly influenced the decline rate of E. coli O157: H7 in manure with the fastest decline in manure from the pure straw diet and the slowest in manure from the grass-silage + maize-silage diet. Roughage type showed no effect on the rate of decline of Salmonella serovar Typhimurium, although decline was significantly faster in the manure derived from straw compared to the manure from the grass-silage + maize-silage diet. The pH and fiber content of the manure were significant explanatory factors and were positively correlated with the rate of decline. With E. coli O157:H7 there was a trend of faster decline in organic compared to conventional soils. No pathogens were detected in the edible lettuce parts. The results indicate that cattle diet and soil management are important factors with respect to the survival of human pathogens in the environment.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • van Bruggen, Ariena, Promotor
  • Termorshuizen, Aad, Co-promotor
Award date26 Oct 2007
Place of Publication[S.l.]
Print ISBNs9789085047285
Publication statusPublished - 2007

Keywords

  • lactuca sativa
  • lettuces
  • food contamination
  • escherichia coli
  • salmonella typhimurium
  • farmyard manure
  • risk factors
  • microbial ecology
  • soil
  • organic farming
  • organic foods
  • primary production

Fingerprint

Dive into the research topics of 'Ecology and risk assessment of E. coli O157:H7 and Salmonella typhimurium in the primary production chain of lettuce'. Together they form a unique fingerprint.

Cite this