title: Quantification of contamination of lettuce by GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium.
abstract: The primary objective of this study was to determine the possibility of internalization of GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. Typhimurium) strains MAE 110 (multi-cellular morphology) and 119 (wild type morphology) into lettuce seedlings (Lactuca sativa cv. Tamburo) grown in an inoculated hydroponic and soil system. The second aim was to quantify the level of contamination with the use of a proper surface sterilization method. Silver nitrate was superior in reducing the number of viable bacteria on leave surfaces compared to sodium hypochlorite and ethanol. With the hydroponic system internal colonization of lettuce only occurred at high densities with S. Typhimurium MAE 119. With the soil system E. coli O157:H7, S. Typhimurium 110 and S. Typhimurium 119 were found at considerable densities in sterilized leaf samples (respectively, 3.95, 2.57 and 2.37 log cfu/g on average) with prevalences of 0.29, 0.23 and 0.15, respectively. No statistical differences were observed between the Salmonella strains. A negative correlation was observed between shoot weight and leaf contamination. The observed presence of the pathogens in lettuce, after thorough surface sterilization, demonstrates the possible presence of human pathogens in locations were they are unlikely to be removed by the actions of consumer washing and therefore pose a serious threat when occurring in field situations.
authors.affiliation: Biological Farming Systems Group, Department of Plant Sciences, Wageningen University and Research Center, Marijkeweg 22, 6709 PG Wageningen, The Netherlands. eelco.franz@wur.nl
authors.forename: Eelco
authors.initials: E
authors.lastname: Franz
authors.forename: Anna A
authors.initials: AA
authors.lastname: Visser
authors.forename: Anne D
authors.initials: AD
authors.lastname: Van Diepeningen
authors.forename: Michel M
authors.initials: MM
authors.lastname: Klerks
authors.forename: Aad J
authors.initials: AJ
authors.lastname: Termorshuizen
authors.forename: Ariena H C
authors.initials: AH
authors.lastname: van Bruggen
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D006801:Humans; D018545:Lactuca / Q000382:microbiology*; D015995:Prevalence; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000254:growth & development
chemical_list: D000900:Anti-Bacterial Agents