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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    Improvement of methods for the detection of Gram-negative foodborne pathogens
    Margot, H.F.T. - \ 2016
    Wageningen University. Promotor(en): Marcel Zwietering; Han Joosten, co-promotor(en): R. Stephan. - Wageningen : Wageningen University - ISBN 9789462578708 - 158
    gram negative bacteria - pathogens - foodborne pathogens - detection - real time pcr - salmonella - escherichia coli - mung beans - gramnegatieve bacteriën - pathogenen - voedselpathogenen - detectie - real time pcr - salmonella - escherichia coli - mungbonen

    Foodborne diseases are a major source of morbidity and mortality worldwide. In most cases, these diseases are caused by contaminated food products, but transmission can also subsequently occur via person to person contact. The ability to detect the pathogens is an important aspect in the verification of food safety. A major proportion of foodborne disease is caused by Gram-negative bacteria. In this thesis, the detection of Gram-negative foodborne pathogens is addressed by looking at the successive steps from enrichment to detection with Salmonella, Shiga toxin-producing E. coli and Cronobacter spp. as example pathogens. The detection of foodborne pathogens using microbiological culture media aiming at the resuscitation and growth of bacteria is still regarded as the gold standard and included in many reference methods. However, cultural methods are time and labour-intensive. Since an immediate response is required in case of contamination and during outbreaks there is a strong interest in methods that deliver information on the microbiological status of the product as quickly and reliable as possible. Rapid cultural methods and commercially available real-time PCR systems for the detection of Salmonella and STEC were compared with regards to their sensitivity and specificity. It was shown that most of the marketed systems are as reliable as the standard methods. However, false-positive results were obtained with real-time PCR systems for the detection of Salmonella. Rapid cultural methods that were based on procedures without the pre-enrichment step, reduced the time to detection but did show some ambiguous results with difficult matrices such as tea. Of the seven rapid tests for the detection of STEC, one did not detect relevant Stx subtypes.

    In order to be detected, pathogens need to multiply to reach a minimum threshold level. However, because they are often sublethally injured due to hostile processing and storage conditions, they first need to be resuscitated. For most pathogens, (Salmonella, STEC and Cronobacter spp.) the first step in the detection is an enrichment including resuscitation in a non-selective medium such as BPW. Modifications to BPW were compared with respect to their ability to promote growth of unstressed and stressed Gram-negative pathogens. The aim was to develop a medium that could be used for the enrichment of pathogens in horizontal methods using only one enrichment step. The resuscitation of stressed Cronobacter cells was improved in BPW supplemented with an additional iron source and sodium pyruvate along with low levels of compounds for the inhibition of Gram-positive bacteria. However, it was observed that BPW containing these supplements allowed for less resuscitation of STEC when compared to regular BPW. Based on these results it was concluded that the application of a one-broth enrichment in food products with a high number of competing bacteria is not recommended due to the overgrowth of the target bacteria. Limitations of the current method for the detection of STEC from sprouted seeds were noticed. Therefore, the growth of stressed STEC cells from different serotypes was assessed in media used for the enrichment of Enterobacteriaceae. In addition, the growth of STEC was examined in the enrichment of sprouts using different media and incubation temperatures. It was shown that the high level of competitors was inhibiting the detection of the target pathogen and that the similarity of target and competing bacteria prevents the design of a selective enrichment procedure. In order to get a better insight in the enrichment ecology, the microbiome of mungo bean sprouts was analysed using Illumina HiSeq sequencing prior to and during the enrichment in BPW and EE-broth at different temperatures. The majority of the sprout flora was composed of bacteria belonging to the phylum Proteobacteria. Enrichment in BPW increased the proportion of Firmicutes whereas the incubation in EE-broth enriched Proteobacteria. The results point out that with the application of a selective medium like EE-broth, growth of the competitive microflora that complicates the detection of STEC is promoted. It was shown that EE-broth also resulted in good growth of STEC however, the problematic situation of low maximum population densities of the target strain in the matrix is still present. The probability of detection is not only influenced by the natural flora of a food product, but also by the physiological state of the pathogen. The influence of stress on the lag time of single cells and the resulting probability of detection were determined for Cronobacter spp. in powdered infant formula. Lag time was calculated from optical density measurement data and different scenarios were modelled. Lag time was longest after acid stress and lag time increase coincided with increased lag time variability. The probability of detection, however, depended both on the sampling plan and on the duration of the lag phase.

    This thesis provides a critical evaluation of rapid methods and valuable new insights on enrichment procedures, the role of competitors in bacterial enrichment procedures and the limitations of selective agents. This information will be of great help to further improve microbiological methods and thereby contribute to more effective management of food safety.

    Salmonella spp. in the feed chain in the Netherlands : monitoring results of five years (2008 to 2012)
    Yassin, H. ; Adamse, P. ; Fels, H.J. van der - \ 2015
    Wageningen : RIKILT Wageningen UR (RIKILT report 2015.005) - 131
    salmonella - voedselpathogenen - veevoederindustrie - voer - voederveiligheid - voedselonderzoek - monitoring - salmonella - foodborne pathogens - feed industry - feeds - feed safety - food research - monitoring
    Salmonella spp. is an important food-borne pathogen in humans. In the Netherlands, monitoring Salmonella spp. in the feed and food chain has become an important issue since 1997. Monitoring results from different sectors, such as broiler meat and eggs, are analysed annually to determine the prevalence of Salmonella spp. The objective of this study was to analyse Salmonella spp. prevalence in feed materials in the Netherlands during the years 2008-2012. Data from the Dutch feed industry, stored in the GMP+ monitoring database, were provided by the Dutch Product Board Animal Feed for use in the current study. These data included results of, on average, 10080 compound feed and 9109 feed material samples per year. This high total number of samples reflects the intensive monitoring program in the Netherlands.
    Impact of climate change on microbial safety of leafy green vegetables
    Liu, C. - \ 2015
    Wageningen University. Promotor(en): Rik Leemans, co-promotor(en): Nynke Hofstra; Eelco Franz. - Wageningen : Wageningen University - ISBN 9789462574403 - 129
    klimaatverandering - bladgroenten - groenten - voedselveiligheid - micro-organismen - besmetting - voedselbesmetting - escherichia coli - salmonella - climatic change - leafy vegetables - vegetables - food safety - microorganisms - contamination - food contamination - escherichia coli - salmonella


    Climate change is generally recognized as a major threat to humans and the environment. With respect to food production, climate change does not only affect crop production or food security, but possibly also effects on food safety by affecting the prevalence and levels of bacteria, fungi or other pests and pesticides. Fresh-cut or ready-to-eat leafy vegetables (e.g. lettuce and spinach) are increasingly consumed because they are promoted as part of a healthy diet. Such leafy green vegetables (LGVs) are identified as the fresh produce commodity group of highest concern from a microbiological safety perspective, because they are often grown in the open field and therefore vulnerable to contamination and contact with (faeces of) wildlife. Moreover, they are grown and consumed in large volumes and often consumed raw. Bacteria, such as Salmonella spp. and pathogenic Escherichia coli strains are the main pathogens causing foodborne disease through LGVs. A major knowledge gap is understanding how climate change may directly or indirectly affect the contamination of LGVs. This primarily relates to the current lack of methods and tools to link climate data and climate change scenarios to food safety.

    My thesis aims to quantify the impacts of climate change on microbial safety of pre-harvested LGVs. To achieve this, I reviewed the literature and synthesised major impacts of climate change on contamination sources and pathways of foodborne pathogens (focussing on Escherichia coli O157 and Salmonella spp.) on pre-harvested LGVs (Chapter 2). Subsequently, I developed a statistical model that identifies the weather and management variables that are associated with the LGVs contamination with generic E. coli using regression analysis (Chapter 3). To apply suitable climate data to this statistical model to assess future impacts, I have prepared a tool to downscale coarse climate and climate change data for local food safety scenario analysis (Chapter 4). Finally, I applied the downscaled data to the statistical model and used multi-criteria scenario analysis to explore future food safety (Chapter 5). E.coli is used as a hygienic indicator in this thesis to study microbial safety of LGVs. Its presence is indicative for an increased pathogen presence probability. E. coli and many foodborne bacteria share the same contamination pathways and climate change is expected to similarly impact on both bacteria. Hygienic status is therefore used in my thesis as a proxy for the microbial safety of LGVs.

    The major result of the literature review in Chapter 2 is that the impact of climate change on LGV contamination depends on the resulting local balance of the positive and negative impacts. The review shows that the interactions between climate change and contamination are real but poorly understood. Therefore, integrative quantitative modelling approaches with scenario analyses and additional laboratory experiments are needed.

    With this knowledge background, mixed effect logistic regression and linear regression models were developed to identify the climate and management variables that are associated with the presence and concentration of E. coli on LGVs (Chapter 3). These models used E. coli data of 562 lettuce and spinach samples taken between 2011 and 2013 from 23 open-field farms from Belgium, Brazil, Egypt, Norway and Spain. Weather and agriculture management practices together had a systematic influence on E.coli presence and concentration. Temperature explained most of the observed variation on E. coli prevalence and concentration on LGVs. Minimum temperature of the sampling day (odds ratio [OR] 1.47), region and application of inorganic fertilizer explained a significant amount of variation in E. coli prevalence. Maximum temperature on three days before sampling and region best explained the variation in E. coli concentration (R2= 0.75). Region is a variable masking many management variables including use of rain water, surface water, manure, inorganic fertilizer and spray irrigation. Climate variables and E. coli presence and concentration are positively related. The results indicate that climate change will have an impact on microbiological safety of LGVs. These impacts can be directly through an increasing temperature, but also indirectly through changes in irrigation water type, fertilizer type and irrigation method. Therefore, climate change and farm management should be considered more systematically in an integrated way in future studies on fresh produce safety.

    To prepare climate data for local food safety scenario analysis, a climate data downscaling tool was presented and demonstrated (Chapter 4). Coarse gridded data from two general circulation models, HadGEM2-ES and CCSM4, were selected and downscaled using the ‘Delta method’ with quantile-quantile correction for the Belgium meteorological station in Ukkel. Observational daily temperature and precipitation data from 1981 to 2000 were used as a reference period for this downscaling. Data were provided for four future representative concentration pathways (RCPs) for the periods 2031–2050 and 2081–2100. These RCPs are radiative forcing scenarios for which future climate conditions are projected. The climate projections for these RCPs show that both temperature and precipitation will increase towards the end of the century in Ukkel. The climate change data were subsequently used with Ratkowsky's bacterial growth model to illustrate how projected climate data can be used for projecting bacterial growth in the future. In this example, the future growth rate of Lactobacillus plantarum and the number of days that the bacteria are able to grow are both projected to increase in Ukkel. This example illustrates that this downscaling method can be applied to assess future food safety. This downscaling tool is relatively straightforward compared to other more complex downscaling tools, so the food safety researchers can easily understand and apply it to their impact studies.

    With the statistical model (Chapter 3) and downscaled climate data (Chapter 4), a multi-criteria scenario analysis tool was developed to explore future food safety using pre-harvest spinach in Spain as an example (Chapter 5). The future E. coli concentrations on spinach were projected to change in RCP 8.5 and RCP 2.6 by the end of the century in Spain. The E. coli concentration was projected to increase between 0.2 log10 CFU/g and 0.3 log10 CFU/g (depending on the climate scenarios and management options applied) due to higher temperature by the end of the century compared to the concentrations by the end of the last century. This comparison assumed no changes in agricultural management practices. This tool can be used to help selecting the best management practices considering climate change and other indicators.

    The pioneering research presented in my thesis brought new methods and tools, and another mind set to food safety research. The climate-change data downscaling tool provides detailed temporal and spatial climate data for climate scenario analysis in food safety assessment studies. The multi-criteria scenario analysis tool provides a platform to study changes in weather or climate, and management impacts on future food safety. This tool also allows for inclusion of different stakeholders’ perspectives or interests and supports their decision making processes. Moreover, the thesis presents a statistical model that can be used to study the relationship between climate and E. coli contamination.

    My thesis quantified the impacts of climate change on microbial safety of pre-harvested LGVs contaminated with generic E. coli for the first time. With one degree increase in minimum temperature of the sampling day, the odds of having E. coli presence on LGVs increase by a factor of 1.5. The mean E. coli concentrations are also expected to increase. Climate change should not be ignored in food safety management and research.

    Inactivation of chemical and heat-resistant spores of Bacillus and Geobacillus by nitrogen cold atmospheric plasma and comparison to thermal and chemical based methods
    Bokhorst-van de Veen, H. van; Xie, H. ; Esveld, D.C. ; Abee, T. ; Mastwijk, H.C. ; Nierop Groot, M.N. - \ 2015
    Food Microbiology 45 (2015)part A. - ISSN 0740-0020 - p. 26 - 33.
    low-temperature - gas plasma - subtilis spores - sterilization - salmonella - decontamination - microorganisms - hypochlorite - germination
    Bacterial spores are resistant to severe conditions and form a challenge to eradicate from food or food packaging material. Cold atmospheric plasma (CAP) treatment is receiving more attention as potential sterilization method at relatively mild conditions but the exact mechanism of inactivation is still not fully understood. In this study, the biocidal effect by nitrogen CAP was determined for chemical (hypochlorite and hydrogen peroxide), physical (UV) and heat-resistant spores. The three different sporeformers used are Bacillus cereus a food-borne pathogen, and Bacillus atrophaeus and Geobacillus stearothermophilus that are used as biological indicators for validation of chemical sterilization and thermal processes, respectively. The different spores showed variation in their degree of inactivation by applied heat, hypochlorite, hydrogen peroxide, and UV treatments, whereas similar inactivation results were obtained with the different spores treated with nitrogen CAP. G. stearothermophilus spores displayed high resistance to heat, hypochlorite, hydrogen peroxide, while for UV treatment B. atrophaeus spores are most tolerant. Scanning electron microscopy analysis revealed distinct morphological changes for nitrogen CAP-treated B. cereus spores including etching effects and the appearance of rough spore surfaces, whereas morphology of spores treated with heat or disinfectants showed no such changes. Moreover, microscopy analysis revealed CAP-exposed B. cereus spores to turn phase grey conceivably because of water influx indicating damage of the spores, a phenomenon that was not observed for non-treated spores. In addition, data are supplied that exclude UV radiation as determinant of antimicrobial activity of nitrogen CAP. Overall, this study shows that nitrogen CAP treatment has a biocidal effect on selected Bacillus and Geobacillus spores associated with alterations in spore surface morphology and loss of spore integrity.
    Enterobacteriaceae rsistant to third-generation cephalosporins and quinolones in fresh culinary herbs imported from Southeast Asia
    Veldman, K.T. ; Kant, A. ; Dierikx, C.M. ; Essen-Zandbergen, A. van; Wit, B. ; Mevius, D.J. - \ 2014
    International Journal of Food Microbiology 177 (2014). - ISSN 0168-1605 - p. 72 - 77.
    escherichia-coli o157-h7 - klebsiella-pneumoniae - molecular characterization - extended-spectrum - antimicrobial resistance - high prevalence - salmonella - lactamase - thailand - determinants
    Since multidrug resistant bacteria are frequently reported from Southeast Asia, our study focused on the occurrence of ESBL-producing Enterobacteriaceae in fresh imported herbs from Thailand, Vietnam and Malaysia. Samples were collected from fresh culinary herbs imported from Southeast Asia in which ESBL-suspected isolates were obtained by selective culturing. Analysis included identification by MALDI-TOF mass spectrometry, susceptibility testing, XbaI-PFGE, microarray, PCR and sequencing of specific ESBL genes, PCR based replicon typing (PBRT) of plasmids and Southern blot hybridization. In addition, the quinolone resistance genotype was characterized by screening for plasmid mediated quinolone resistance (PMQR) genes and mutations in the quinolone resistance determining region (QRDR) of gyrA and parC. The study encompassed fifty samples of ten batches of culinary herbs (5 samples per batch) comprising nine different herb variants. The herbs originated from Thailand (Water morning glory, Acacia and Betel leaf), Vietnam (Parsley, Asian pennywort, Houttuynia leaf and Mint) and Malaysia (Holy basil and Parsley). By selective culturing 21 cefotaxime resistant Enterobacteriaceae were retrieved. Array analysis revealed 18 isolates with ESBL genes and one isolate with solely non-ESBL beta-lactamase genes. Mutations in the ampC promoter region were determined in two isolates with PCR and sequencing. The isolates were identified as Klebsiella pneumoniae (n = 9), Escherichia coli (n = 6), Enterobacter cloacae complex (n = 5) and Enterobacter spp. (n = 1). All isolates tested were multidrug resistant. Variants of CTX-M enzymes were predominantly found followed by SHV enzymes. PMQR genes (including aac(6')-1b-cr, qnrB and qnrS) were also frequently detected. In almost all cases ESBL and quinolone resistance genes were located on the same plasmid. Imported fresh culinary herbs from Southeast Asia are a potential source for contamination of food with multidrug resistant bacteria. Because these herbs are consumed without appropriate heating, transfer to human bacteria cannot be excluded.
    REG3¿-deficient mice have altered mucus distribution and increased mucosal inflammatory responses to the microbiota and enteric pathogens in the ileum
    Loonen, L.M.P. ; Kranenbarg-Stolte, H.H. ; Jaklofsky, M.T.J. ; Meijerink, M. ; Dekker, J. ; Baarlen, P. van; Wells, J. - \ 2014
    Mucosal Immunology 7 (2014). - ISSN 1933-0219 - p. 939 - 947.
    pancreatitis-associated protein - bacterial aggregation - dietary calcium - bowel-disease - regiii-gamma - expression - salmonella - infection - lectin - rats
    REG3¿ is considered to have a protective role against infection with Gram-positive bacteria due to its bactericidal activity, but evidence from in vivo studies is lacking. We generated a REG3¿-/- mouse, and investigated the effect of lack of REG3¿ on intestinal mucus distribution, spatial compartmentalization of bacteria, and expression of innate immunity genes. Infection studies were also performed with Gram-positive and Gram-negative pathogens to investigate the antimicrobial role of REG3¿. REG3¿-/- mice display altered mucus distribution, increased bacterial contact with the epithelium, and elevated inflammatory markers in the ileum without histological evidence of pathology. Infection response pathway genes were differentially expressed in both Listeria monocytogenes and Salmonella enteritidis infected REG3¿-/- and wild-type (wt) mice. Higher amounts of myeloperoxidase and interleukin-22 transcripts were present in the ileal mucosa of REG3¿-/- than wt mice, but translocation to the organs was unaffected. We concluded that REG3¿ has a protective role against mucosal infection with pathogenic Listeria and Salmonella in vivo. REG3¿ is equally distributed throughout the mucus and its absence results in increased epithelial contact with the microbiota resulting in low-grade inflammation. REG3¿ can bind to Gram-negative and Gram-positive bacteria and influence mucus distribution in the ileum, properties which may contribute to mucosal protection.
    Characteristics of Cefotaxime-Resistant Escherichia coli from Wild Birds in The Netherlands
    Veldman, K.T. ; Tulden, P. ; Kant, A. ; Testerink, J.J. ; Mevius, D.J. - \ 2013
    Applied and Environmental Microbiology 79 (2013)24. - ISSN 0099-2240 - p. 7556 - 7561.
    spectrum-beta-lactamase - extended-spectrum - antibiotic-resistance - natural reserve - ctx-m - salmonella - plasmids - gulls - enterobacteriaceae - environments
    Cloacal swabs from carcasses of Dutch wild birds obtained in 2010 and 2011 were selectively cultured on media with cefotaxime to screen for the presence of extended-spectrum beta-lactamase (ESBL)/AmpC-producing Escherichia coli. Subsequently, all cefotaxime-resistant E. coli isolates were tested by broth microdilution and microarray. The presence of ESBL/AmpC and coexisting plasmid-mediated quinolone resistance (PMQR) genes was confirmed by PCR and sequencing. To determine the size of plasmids and the location of ESBL and PMQR genes, S1 pulsed-field gel electrophoresis (PFGE) was performed on transformants, followed by Southern blot hybridization. The study included 414 cloacal swabs originating from 55 different bird species. Cefotaxime-resistant E. coli isolates were identified in 65 birds (15.7%) from 21 different species. In all, 65 cefotaxime-resistant E. coli ESBL/AmpC genes were detected, mainly comprising variants of bla(CTX-M) and bla(CMY-2). Furthermore, PMQR genes [aac(6')-lb-cr, qnrB1, and qnrS1] coincided in seven cefotaxime-resistant E. coli isolates. Overall, replicon typing of the ESBL/AmpC-carrying plasmids demonstrated the predominant presence of IncI1 (n = 31) and variants of IncF (n = 18). Our results indicate a wide dissemination of ESBL and AmpC genes in wild birds from The Netherlands, especially among aquatic-associated species (waterfowl, gulls, and waders). The identified genes and plasmids reflect the genes found predominantly in livestock animals as well as in humans.
    Salmonella biofilms
    Castelijn, G.A.A. - \ 2013
    Wageningen University. Promotor(en): Tjakko Abee; Marcel Zwietering, co-promotor(en): Roy Moezelaar. - S.l. : s.n. - ISBN 9789461737335 - 168
    salmonella typhimurium - salmonella - biofilms - franjes - salmonella typhimurium - salmonella - biofilms - fimbriae

    Biofilm formation by Salmonellaspp. is a problem in the food industry, since biofilms may act as a persistent source of product contamination. Therefore the aim of this study was to obtain more insight in the processes involved and the factors contributing to Salmonellabiofilm formation. A collection of SalmonellaTyphimurium clinical, outbreak-related and retail product isolates, was used to determine biofilm formation capacity and to identify cellular parameters contributing to surface colonisation. The results revealed dense biofilm formation by these isolates at 25 °C and 37 °C in nutrient-rich media. However, in nutrient-low media dense biofilm formation was only observed at 25 °C with industrial isolates. In addition, temperature and medium composition were also found to influence biofilm morphology and composition. At nutrient-low conditions at 25 °C the biofilm consisted of cell clusters encapsulated by an extracellular matrix composed of curli fimbriae and cellulose. In nutrient-rich conditions a monolayer of cells with little to no extracellular matrix were observed, with a prominent role for type 1 fimbriae. This type of fimbriae was only expressed in a subset of strains and appeared to contribute to initial attachment of Salmonellacells ultimately leading to dense biofilm formation. This study also indicated that biofilm formation differs between and within the Salmonellaserovars Typhimurium, Derby, Brandenburg and Infantis, isolated from meat processing environments. And, for all serovars biofim formation contributed to the survival on stainless steel surfaces and biofilm cells were less susceptible to peracetic acid disinfection treatments. This latter effect was specifically observed in the presence of organic matter, which drastically decreased the activity of peracetic acid conceivably resulting in low level exposure of the bacterial flora facilitating survival. Furthermore, single and repeated exposure to sub-lethal concentrations of the disinfectant benzalkonium chloride rapidly selected for resistant variants. In conclusion, the results obtained in this study may contribute to the development of better strategies for Salmonella control in food processing environments.

    Comprehensive analysis of B-Lactam antibiotics including penicillins, cephalosporins and carbapenems in poultry muscle using liquid chromatography coupled to tandem mass spectrometry
    Berendsen, B.J.A. ; Gerritsen, H.W. ; Wegh, R.S. ; Lameris, S.L. ; Sebille, R. van; Stolker, A.A.M. ; Nielen, M.W.F. - \ 2013
    Analytical and Bioanalytical Chemistry 405 (2013)24. - ISSN 1618-2642 - p. 7859 - 7874.
    beta-lactamase - quantitative-analysis - ceftiofur resistance - escherichia-coli - european-union - bovine muscle - kidney tissue - enterobacteriaceae - salmonella - mechanisms
    A comprehensive method for the quantitative residue analysis of trace levels of 22 ß-lactam antibiotics, including penicillins, cephalosporins, and carbapenems, in poultry muscle by liquid chromatography in combination with tandem mass spectrometric detection is reported. The samples analyzed for ß-lactam residues are hydrolyzed using piperidine in order to improve compound stability and to include the total residue content of the cephalosporin ceftifour. The reaction procedure was optimized using a full experimental design. Following detailed isotope labeling, tandem mass spectrometry studies and exact mass measurements using high-resolution mass spectrometry reaction schemes could be proposed for all ß-lactams studied. The main reaction occurring is the hydrolysis of the ß-lactam ring under formation of the piperidine substituted amide. For some ß-lactams, multiple isobaric hydrolysis reaction products are obtained, in accordance with expectations, but this did not hamper quantitative analysis. The final method was fully validated as a quantitative confirmatory residue analysis method according to Commission Decision 2002/657/EC and showed satisfactory quantitative performance for all compounds with trueness between 80 and 110 % and within-laboratory reproducibility below 22 % at target level, except for biapenem. For biapenem, the method proved to be suitable for qualitative analysis only.
    Uitbraak Salmonella in zalm (interview met o.a. M.H. Zwietering)
    Zwietering, Marcel - \ 2012
    food safety - food contamination - salmonella - salmon - inspection
    Microbial performance of food safety management systems implemented in the lamb production chain
    Oses, S.M. ; Luning, P.A. ; Jacxsens, L. ; Santillana, S. ; Jaime, I. ; Rovira, J. - \ 2012
    Journal of Food Protection 75 (2012)1. - ISSN 0362-028X - p. 95 - 103.
    escherichia-coli o157 - beef processing plants - aerobic-bacteria - red meat - carcasses - prevalence - contamination - enterobacteriaceae - campylobacter - salmonella
    The actual microbial status of the lamb production chain at three slaughterhouses, one processing plant, and five butcher shops selling whole or cut lamb carcasses to consumers was assessed with a previously developed microbial assessment scheme. All studied establishments had a food safety management system (FSMS) that was implemented according to legislative requirements. Microbial safety level profiles were constructed for each establishment and provided clear indications of which pathogens, hygiene indicators, or utility parameters required attention to improve the performance of the microbiological control protocols of the implemented FSMS. The highest contamination was found in the slaughterhouses in samples taken from the meat products (aerobic mesophilic plate counts [AMPs] of 3.40 to 6.63 log CFU/cm(2) and Enterobacteriaceae counts of 1.00 to 4.62 log CFU/cm(2)), contact surfaces (AMPs of 2.44 to 8.92 log CFU/cm(2)), and operators' hands and/or gloves (AMPs of 2.84 to 8.09 log CFU/cm(2)), especially after hide removal and evisceration. The microbial assessment scheme is a useful tool for providing insight into the actual microbiological results achieved with an FSMS implemented in establishments at various stages along the lamb production chain.
    Detection and characterization of pCT-like plasmid vectors for blaCTX-M-14 in Escherichia coli isolates from humans, turkeys and cattle in England and Wales
    Stokes, M.O. ; Cottel, J.L. ; Piddock, L.J. ; Wu, G. ; Wootton, M. ; Mevius, D.J. ; Randall, L.P. ; Teale, C.J. ; Fielder, M.D. ; Coldham, N.G. - \ 2012
    Journal of Antimicrobial Chemotherapy 67 (2012)7. - ISSN 0305-7453 - p. 1639 - 1644.
    spectrum-beta-lactamase - ctx-m - salmonella - ctx-m-14 - enterobacteriaceae - resistance - strains - france - gene - uk
    Objectives - To detect and characterize Escherichia coli strains and pCT-like plasmids implicated in the dissemination of the CTX-M-14 gene in animals and humans, in England and Wales. Methods UK CTX-M-14-producing E. coli (n¿=¿70) from cattle (n¿=¿33), turkeys (n¿=¿9), sheep (n¿=¿2) and humans (n¿=¿26) were screened using multiplex PCR for the detection of a previously characterized plasmid, pCT. Isolates found to be carrying two or more pCT genetic markers were further analysed using PFGE. Their antimicrobial-resistance genes and virulence genes were also determined. These plasmids were transferred to Salmonella enterica serotype Typhimurium 26R and further examined for incompatibility type, genetic environment of the blaCTX-M-14 gene, size, restriction fragment length polymorphism (RFLP) and nikB sequence. Results - The 25 E. coli isolates carrying pCT genetic markers generated 19 different PFGE profiles, and 23 isolates had different virulence and antimicrobial-resistance gene patterns. One isolate from cattle was a verotoxigenic E. coli (‘VTEC’); the rest were commensal or extra-intestinal pathogenic E. coli. pCT-like plasmids with similar molecular characteristics (size, replicon type, RFLP pattern, pCT markers and genetic environment of the blaCTX-M-14 gene) were detected in 21/25 of the field isolates, which comprised those from cattle (n¿=¿9), turkeys (n¿=¿8) and humans (n¿=¿4). All pCT-like plasmids were conjugative, and most were IncK (n¿=¿21) and had the same local genetic environment flanking the blaCTX-M-14 gene (n¿=¿23). RFLP analysis demonstrated =75% similarity among most plasmids (n¿=¿22). Conclusions - pCT-like plasmids were common vectors for horizontal dissemination of 30% of the blaCTX-M-14 genes to
    Interaction effects between sender and receiver processes in indirect transmission of Campylobacter jejuni between broilers.
    Bunnik, B.A.D. van; Hagenaars, T.H.J. ; Bolder, N.M. ; Nodelijk, G. ; Jong, M.C.M. de - \ 2012
    BMC Veterinary Research 8 (2012). - ISSN 1746-6148
    swine-fever virus - drinking-water - netherlands - epidemic - quantification - salmonella - resistance - bacteria - evaluate - design
    Background: Infectious diseases in plants, animals and humans are often transmitted indirectly between hosts (or between groups of hosts), i.e. via some route through the environment instead of via direct contacts between these hosts. Here we study indirect transmission experimentally, using transmission of Campylobacter jejuni (C. jejuni) between spatially separated broilers as a model system. We distinguish three stages in the process of indirect transmission; (1) an infectious "sender" excretes the agent, after which (2) the agent is transported via some route to a susceptible "receiver", and subsequently (3) the receiver becomes colonised by the agent. The role of the sender and receiver side (stage 1 and stage 3) was studied here by using acidification of the drinking water as a modulation mechanism. Results: In the experiment one control group and three treatment groups were monitored for the presence of C. jejuni by taking daily cloacal swabs. The three treatments consisted of acidification of the drinking water of the inoculated animals (the senders), acidification of the drinking water of the susceptible animals (the receivers) or acidification of the drinking water of both inoculated and susceptible animals. In the control group 12 animals got colonised out of a possible 40, in each treatment groups 3 animals out of a possible 40 were found colonised with C. jejuni. Conclusions: The results of the experiments show a significant decrease in transmission rate (beta) between the control groups and treatment groups (p <0.01 for all groups) but not between different treatments; there is a significant negative interaction effect when both the sender and the receiver group receive acidified drinking water (p = 0.01). This negative interaction effect could be due to selection of bacteria already at the sender side thereby diminishing the effect of acidification at the receiver side.
    Reusing salad from salad bars – simulating the effects on product loss, microbial safety and product quality
    Tromp, S.O. ; Rijgersberg, H. ; Franz, E. - \ 2012
    International Journal of Food Science and Technology 47 (2012)6. - ISSN 0950-5423 - p. 1144 - 1150.
    listeria-monocytogenes - iceberg lettuce - risk-assessment - outbreak - restaurant - salmonella - growth - sustainability - contamination - challenges
    The goal of this study is to model the effects of reusing salad from salad bars to reduce product loss, while keeping microbial safety and product quality at acceptable levels. We, therefore, expand our previously developed simulation model by incorporating reuse strategies and a quality decay model. The expanded model is used to simulate different salad reuse scenarios and to quantify the consequences to product loss, microbial safety and product quality. With this study, we show an application of a generic approach for the integrated modelling of product loss, microbial safety and product quality. The most cautious scenario consists of reusing salad for only 1 day after the first use and only if the salad originates from a package with a valid best-before date at the time of reuse (‘minimum reuse of salad with the best-before date criterion’). This scenario decreases product loss at the salad bar considerably from 37% to 29% ()21%). This considerable benefit occurs almost without causing product loss at the cold storage (increase from 0% to 1%), with only a minimal increase in the number of foetal mortality cases because of Listeria monocytogenes (increase from 11.9 to 12.2 cases per year (+3%)) and hardly any decline in product quality
    Supplemental Antioxidants Do Not Ameliorate Colitis Development in HLA-B27 Transgenic Rats Despite Extremely Low Glutathione Levels in Colonic Mucosa
    Schepens, M.A.A. ; Vink, C. ; Schonewille, A.J. ; Roelofs, H.M.J. ; Brummer, R.J. ; Meer, R. van der; Bovee-Oudenhoven, I.M.J. - \ 2011
    Inflammatory Bowel Diseases 17 (2011)10. - ISSN 1078-0998 - p. 2065 - 2075.
    inflammatory-bowel-disease - dietary calcium - ulcerative-colitis - salmonella - cancer - cells - permeability - prevention - nutrition - radicals
    Background: Oxidative stress is presumed to play an important role in inflammatory bowel disease (IBD). Accordingly, antioxidant supplementation might be protective. Dietary calcium inhibited colitis development in HLA-B27 transgenic rats, an animal model mimicking IBD. As antioxidants might act at mucosa level and calcium predominantly in the gut lumen, we hypothesize that the combination has additive protective effects on colitis development. Methods: HLA-B27 rats were fed a control diet or the same diet supplemented with the antioxidants glutathione, vitamin C, and vitamin E, or supplemented with both antioxidants and calcium. Oxidative stress in colonic mucosa, colonic inflammation, intestinal permeability, and diarrhea were quantified. Results: Intestinal permeability, diarrhea, myeloperoxidase, and interleukin-1 beta levels were significantly lower in rats fed both antioxidants and calcium compared to rats supplemented with antioxidants only. No beneficial effects were observed in rats fed the diet supplemented with antioxidants only. Strikingly, despite extremely low colonic mucosal glutathione levels in HLA-B27 rats, there was no oxidative stress-related damage. Subsequent analyses showed no defect in expression of glutathione synthesis genes. Additional experiments, comparing young and older HLA-B27 rats, showed that glutathione levels and also reactive oxygen species production decreased with progression of intestinal inflammation. Conclusions: Antioxidant supplementation was ineffective in HLA-B27 rats despite low mucosal glutathione levels, because colitis development did not coincide with oxidative stress in this model. This indicates that the neutrophilic respiratory burst, and thus innate immune defense, is compromised in HLA-B27 rats. As supplementation with both calcium and antioxidants attenuated colitis development, we speculate that this protective effect is attributed to calcium only.
    Systems biology in animal sciences
    Woelders, H. ; Pas, M.F.W. te; Bannink, A. ; Veerkamp, R.F. ; Smits, M.A. - \ 2011
    Animal 5 (2011)07. - ISSN 1751-7311 - p. 1036 - 1047.
    gene-expression - dairy-cows - mathematical-model - fat synthesis - salmonella - networks - disease - physiology - infection - responses
    Systems biology is a rapidly expanding field of research and is applied in a number of biological disciplines. In animal sciences, omics approaches are increasingly used, yielding vast amounts of data, but systems biology approaches to extract understanding from these data of biological processes and animal traits are not yet frequently used. This paper aims to explain what systems biology is and which areas of animal sciences could benefit from systems biology approaches. Systems biology aims to understand whole biological systems working as a unit, rather than investigating their individual components. Therefore, systems biology can be considered a holistic approach, as opposed to reductionism. The recently developed ‘omics’ technologies enable biological sciences to characterize the molecular components of life with ever increasing speed, yielding vast amounts of data. However, biological functions do not follow from the simple addition of the properties of system components, but rather arise from the dynamic interactions of these components. Systems biology combines statistics, bioinformatics and mathematical modeling to integrate and analyze large amounts of data in order to extract a better understanding of the biology from these huge data sets and to predict the behavior of biological systems. A ‘system’ approach and mathematical modeling in biological sciences are not new in itself, as they were used in biochemistry, physiology and genetics long before the name systems biology was coined. However, the present combination of mass biological data and of computational and modeling tools is unprecedented and truly represents a major paradigm shift in biology. Significant advances have been made using systems biology approaches, especially in the field of bacterial and eukaryotic cells and in human medicine. Similarly, progress is being made with ‘system approaches’ in animal sciences, providing exciting opportunities to predict and modulate animal traits.
    Dietary calcium decreases but short-chain fructo-oligosaccharides increase colonic permeability in rats
    Schepens, M.A.A. ; Rijnierse, A. ; Schonewille, A.J. ; Vink, C. ; Brummer, R.J.M. ; Willemsen, L.E.M. ; Meer, R. van de; Bovee-Oudenhoven, I.M.J. - \ 2010
    The British journal of nutrition 104 (2010)12. - ISSN 0007-1145 - p. 1780 - 1786.
    intestinal permeability - ulcerative-colitis - crohns-disease - fatty-acids - bile-acids - inulin - salmonella - humans - oligofructose - translocation
    An increased intestinal permeability is associated with several diseases. Nutrition can influence gut permeability. Previously, we showed that dietary Ca decreases whereas dietary short-chain fructo-oligosaccharides (scFOS) increase intestinal permeability in rats. However, it is unknown how and where in the gastrointestinal tract Ca and scFOS exert their effects. Rats were fed a Western low-Ca control diet, or a similar diet supplemented with either Ca or scFOS. Lactulose plus mannitol and Cr-EDTA were added to the diets to quantify small and total gastrointestinal permeability, respectively. Additionally, colonic tissue was mounted in Ussing chambers and exposed to faecal water of these rats. Dietary Ca immediately decreased urinary Cr-EDTA excretion by 24 % in Ca-fed rats compared with control rats. Dietary scFOS increased total Cr-EDTA permeability gradually with time, likely reflecting relatively slow gut microbiota adaptations, which finally resulted in a 30 % increase. The lactulose: mannitol ratio was 15 % higher for Ca-fed rats and 16 % lower for scFOS-fed rats compared with control rats. However, no dietary effect was present on individual urinary lactulose and mannitol excretion. The faecal waters did not influence colonic permeability in Ussing chambers. In conclusion, despite effects on the lactulose: mannitol ratio, individual lactulose values did not alter, indicating that diet did not influence small-intestinal permeability. Therefore, both nutrients affect permeability only in the colon: Ca decreases, while scFOS increase colonic permeability. As faecal water did not influence permeability in Ussing chambers, probably modulation of mucins and/or microbiota is important for the in vivo effects of dietary Ca and scFOS.
    Comparison of Campylobacter Levels in Crops and Ceca of Broilers at Slaughter
    Gerwe, T. van; Bouma, A. ; Wagenaar, J.A. ; Jacobs-Reitsma, W.F. ; Stegeman, A. - \ 2010
    Avian Diseases 54 (2010)3. - ISSN 0005-2086 - p. 1072 - 1074.
    jejuni colonization - chickens - contamination - carcasses - feed - spp. - meat - salmonella - water - acids
    considerable fraction of the poultry carcasses becomes contaminated with Campylobacter by cross-contamination from the digestive tract of colonized broilers at slaughter. Campylobacter in the crop may serve as a possible source of cross-contamination, because the crop may contain high numbers of Campylobacter and is more likely to rupture during the slaughtering process than intestines. In this study, the correlation between Campylobacter colonization levels in crop and cecum was assessed in 48 broilers of 31 days of age. In addition, the effect of drinking water supplemented with 0.2% volatile fatty acid (VFA) on these Campylobacter colonization levels was studied. No correlation between crop and cecal colonization levels was found (rho = 0.09; P = 0.71), indicating that future studies on cross-contamination should include an examination of not only cecal colonization levels but also crop colonization levels. Supplementation of drinking water with VFA did not result in a significant reduction of colonization levels in either the crop (P = 0.50) or the ceca (P = 0.92), indicating that this is not an effective measure to reduce cross-contamination at slaughter.
    Medium chain fatty acid feed supplementation reduces the probability of Campylobacter jejuni colonization in broilers
    Gerwe, T. van; Bouma, A. ; Klinkenberg, D. ; Wagenaar, J.A. ; Jacobs-Reitsma, W.F. ; Stegeman, A. - \ 2010
    Veterinary Microbiology 143 (2010)2-4. - ISSN 0378-1135 - p. 314 - 318.
    salmonella - infection - model
    Campylobacteriosis in humans is associated with handling and consumption of contaminated broiler meat. Reduction of the number of Campylobacter-colonized broiler flocks could potentially be realized by decreasing their susceptibility for colonization. The aim of this study was to determine the effect of feed supplementation with a mixture of medium chain fatty acids (C-8-C-12) on susceptibility of broilers for Campylobacter colonization, feed conversion and body weight gain. Two experiments were carried out with individually housed commercial broilers. The birds were fed with medium chain fatty acids supplemented feed (n = 227), or received feed without supplement (n = 87). The birds were inoculated with a dose of Campylobacter jejuni varying between log(10)1.19-5.47 CFU. During 14 days after inoculation, cecal or fecal samples were collected, in which the presence of C jejuni was determined by bacterial culture. Beta-binomial dose-response modeling of the colonization status at 14 days post-inoculation was performed to estimate the C. jejuni dose necessary to colonize 50% of inoculated broilers, which was estimated to be 200 times higher in broilers fed with supplemented feed (log(10)4.8 CFU) than in control broilers (log(10)2.5 CFU). Feed conversion was not affected by feed supplementation, while body weight gain was 49 g higher in broilers fed with supplemented feed. These findings indicate that susceptibility of broilers for Campylobacter colonization is decreased by supplementation with medium chain fatty acids, and that feed supplemented with this mixture may be a promising tool for the reduction of Campylobacter colonization in commercial broiler flocks.
    Risk factors for indigenous Campylobacter jejuni and Campylobacter coli infections in The Netherlands: a case-control study
    Doorduyn, Y. ; Brandhof, W.E. van den; Duynhoven, Y.T.H.P. van; Breukink, B.J. ; Wagenaar, J.A. ; Pelt, W. van - \ 2010
    Epidemiology and Infection 138 (2010)10. - ISSN 0950-2688 - p. 1391 - 1404.
    typhimurium dt104 - young-children - united-states - gastroenteritis - salmonella - disease - outbreak - identification - epidemiology - surveillance
    A case-control study comprising 1315 Campylobacter jejuni cases, 121 Campylobacter coli cases and 3409 frequency-matched controls was conducted in The Netherlands in 2002-2003. Risk factors for both C. jejuni and C. coli enteritis were consumption of undercooked meat and barbecued meat, ownership of cats and use of proton pump inhibitors. Consumption of chicken was a predominant risk factor for C. jejuni enteritis, but many additional risk factors were identified. Unique risk factors for C. coli infections were consumption of game and tripe, and swimming. Contact with farm animals and persons with gastroenteritis were predominant risk factors for C. jejuni enteritis in young children (0-4 years). Important risk factors for the elderly (>= 60 years) were eating in a restaurant, use of proton pump inhibitors and having a chronic intestinal illness. Consumption of chicken in spring, steak tartare in autumn and winter and barbecued meat in rural areas showed strong associations with C. jejuni infections. This study illustrates that important differences in risk factors exist for different Campylobacter spp. and these may differ dependent on age, season or degree of urbanization.
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