Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Dynamics of shiga-toxin producing Escherichia coli (STEC) and their virulence factors in cattle
Dopfer, D.D.V. ; Geue, L. ; Schares, S. ; Mintel, B. ; Hoffmann, B. ; Fischer, E.A.J. - \ 2012
Preventive Veterinary Medicine 103 (2012)1. - ISSN 0167-5877 - p. 22 - 30.
hemolytic uremic syndrome - coli o157-h7 - feedlot cattle - epithelial-cells - multiplex pcr - dna-sequence - strains - plasmid - o157h7 - farms
Starting at birth, twenty Holstein calves were housed individually, in groups of five and finally in one large freestall while fecal samples were collected weekly for 25 weeks. From each sample, twenty isolates of Escherichia coli were screened for 6 virulence markers including shiga-toxin 1, 2, intimin, enterohemolysin, the fimbrial antigen efa1 and the adhesin saa. Dynamic models of transmission of E. coli were used to model the transmission of different virulotypes between calves and the loss of the same virulotypes from the calves. It was found that, once E. coli encoding shiga-toxins in combination with enterohemolysin were transmitted and established in a calf, they tended to be eliminated less efficiently compared to E. coli without this combination of virulence markers. It was concluded that the presence of certain combinations of virulence markers coincided with persistence of E. coli in the bovine gastrointestinal tract. In addition, the combinations of stx with either eae or ehxA in E. coli have a greater impact on the loss rates than on the transmission rates.
Quantitative Microbial Risk Assessment for Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in Leafy Green Vegetables Consumed at Salad Bars, Based on Modeling Supply Chain Logistics
Tromp, S.O. ; Rijgersberg, H. ; Franz, E. - \ 2010
Journal of Food Protection 73 (2010)10. - ISSN 0362-028X - p. 1830 - 1840.
iceberg lettuce - dose-response - fresh produce - growth - outbreaks - foodborne - o157h7 - temperatures - restaurant - infection
Quantitative microbial risk assessments do not usually account for the planning and ordering mechanisms (logistics) of a food supply chain. These mechanisms and consumer demand determine the storage and delay times of products. The aim of this study was to quantitatively assess the difference between simulating supply chain logistics (MOD) and assuming fixed storage times (FIX) in microbial risk estimation for the supply chain of fresh-cut leafy green vegetables destined for working-canteen salad bars. The results of the FIX model were previously published (E. Franz, S. O. Tromp, H. Rijgersberg, and H. J. van der Fels-Klerx, J. Food Prot. 73:274-285, 2010). Pathogen growth was modeled using stochastic discrete-event simulation of the applied logistics concept. The public health effects were assessed by conducting an exposure assessment and risk characterization. The relative growths of Escherichia coli O157 (17%) and Salmonella enterica (15%) were identical in the MOD and FIX models. In contrast, the relative growth of Listeria monocytogenes was considerably higher in the MOD model (1,156%) than in the FIX model (194%). The probability of L. monocytogenes infection in The Netherlands was higher in the MOD model (5.18 × 10-8) than in the FIX model (1.23 × 10-8). The risk of listeriosis-induced fetal mortality in the perinatal population increased from 1.24 × 10-4 (FIX) to 1.66 × 10-4 (MOD). Modeling the probabilistic nature of supply chain logistics is of additional value for microbial risk assessments regarding psychrotrophic pathogens in food products for which time and temperature are the postharvest preventive measures in guaranteeing food safety.
Quantification of contamination of lettuce by GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium
Franz, E. ; Visser, A.A. ; Diepeningen, A.D. van; Klerks, M.M. ; Termorshuizen, A.J. ; Bruggen, A.H.C. van - \ 2007
Food Microbiology 24 (2007)1. - ISSN 0740-0020 - p. 106 - 112.
green fluorescent protein - irrigation water - listeria-monocytogenes - aggregative behavior - bovine manure - leaf lettuce - survival - o157h7 - consumption - infections
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.
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