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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    Antimicrobial peptides and the interplay between microbes and host : towards preventing porcine infections with Streptococcus suis
    Gaiser, Rogier A. - \ 2016
    Wageningen University. Promotor(en): Jerry Wells, co-promotor(en): Peter van Baarlen. - Wageningen : Wageningen University - ISBN 9789462578913 - 239
    antimicrobial peptides - streptococcus suis - infections - bacteria - microorganisms - host pathogen interactions - pigs - antimicrobiële peptiden - streptococcus suis - infecties - bacteriën - micro-organismen - gastheer-pathogeen interacties - varkens

    The increasing prevalence of antibiotic resistance in pathogenic bacteria and the potential future implications for human and animal morbidity and mortality, health-care costs and economic losses pose an urgent worldwide problem. As a result, exploration of alternative strategies to combat antibiotic resistant bacteria have intensified over the last decades. The work described in this thesis focused on the study of naturally occurring antimicrobial peptides (AMPs) and other bioactive molecules produced by bacteria as potential alternatives to prevent or treat infections with pathogenic bacteria. A large part of the thesis aimed to increase knowledge about the role of the microbiota (the collection of microbes present at a certain location of the body) of the oral cavity or small intestine in the abundance of Streptococcus suis, a pathogenic bacteria that mostly causes disease in young pigs. We identified commensal bacteria that displayed strong and selective antagonism against this S. suis. Several bacteria that showed strong growth inhibition of S. suis in the lab through the production of AMPs were isolated and characterised. This thesis increased the understanding of the role of host- and microbiota-derived biologically active small molecules in microbe-microbe and microbe-host interplay. Such knowledge may contribute to the development of novel therapeutic solutions to treat antibiotic resistant bacteria, such as beneficial microbial communities (i.e. next-generation probiotics) or biotechnological applications of natural or modified AMPs.

    Diversity of aquatic Pseudomonas species and their activity against the fish pathogenic oomycete Saprolegnia
    Liu, Y. ; Rzeszutek, E. ; Voort, M. van der; Wu, C.H. ; Thoen, E. ; Skaar, I. ; Bulone, V. ; Dorrestein, P.C. ; Raaijmakers, J.M. ; Bruijn, I. de - \ 2015
    PLoS ONE 10 (2015)8. - ISSN 1932-6203 - 17 p.
    cyclic lipopeptide surfactants - anguilla-australis richardson - media strain a199 - fluorescens - biosynthesis - parasitica - bacteria - chytridiomycosis - aquaculture - infections
    Emerging fungal and oomycete pathogens are increasingly threatening animals and plants globally. Amongst oomycetes, Saprolegnia species adversely affect wild and cultivated populations of amphibians and fish, leading to substantial reductions in biodiversity and food productivity. With the ban of several chemical control measures, new sustainable methods are needed to mitigate Saprolegnia infections in aquaculture. Here, PhyloChip-based community analyses showed that the Pseudomonadales, particularly Pseudomonas species, represent one of the largest bacterial orders associated with salmon eggs from a commercial hatchery. Among the Pseudomonas species isolated from salmon eggs, significantly more biosurfactant producers were retrieved from healthy salmon eggs than from Saprolegnia-infected eggs. Subsequent in vivo activity bioassays showed that Pseudomonas isolate H6 significantly reduced salmon egg mortality caused by Saprolegnia diclina. Live colony mass spectrometry showed that strain H6 produces a viscosin-like lipopeptide surfactant. This biosurfactant inhibited growth of Saprolegnia in vitro, but no significant protection of salmon eggs against Saprolegniosis was observed. These results indicate that live inocula of aquatic Pseudomonas strains, instead of their bioactive compound, can provide new (micro)biological and sustainable means to mitigate oomycete diseases in aquaculture.
    Staphylococcus aureus ST398 gene expression profiling during ex vivo colonization of porcine nasal epithelium
    Tulinski, P. ; Duim, B. ; Wittink, F.R. ; Jonker, M.J. ; Breit, T.M. ; Putten, J.P. van; Wagenaar, J.A. ; Fluit, A.C. - \ 2014
    BMC Genomics 15 (2014). - ISSN 1471-2164
    clumping factor-b - methicillin-resistant - carriage - model - adherence - humans - proteinases - determinant - infections - cells
    Background: Staphylococcus aureus is a common human and animal opportunistic pathogen. In humans nasal carriage of S. aureus is a risk factor for various infections. Methicillin-resistant S. aureus ST398 is highly prevalent in pigs in Europe and North America. The mechanism of successful pig colonization by MRSA ST398 is poorly understood. Previously, we developed a nasal colonization model of porcine nasal mucosa explants to identify molecular traits involved in nasal MRSA colonization of pigs. Results: We report the analysis of changes in the transcription of MRSA ST398 strain S0462 during colonization on the explant epithelium. Major regulated genes were encoding metabolic processes and regulation of these genes may represent metabolic adaptation to nasal mucosa explants. Colonization was not accompanied by significant changes in transcripts of the main virulence associated genes or known human colonization factors. Here, we documented regulation of two genes which have potential influence on S. aureus colonization; cysteine extracellular proteinase (scpA) and von Willebrand factor-binding protein (vWbp, encoded on SaPIbov5). Colonization with isogenic-deletion strains (Delta vwbp and Delta scpA) did not alter the ex vivo nasal S. aureus colonization compared to wild type. Conclusions: Our results suggest that nasal colonization with MRSA ST398 is a complex event that is accompanied with changes in bacterial gene expression regulation and metabolic adaptation.
    Development of novel AllGlo-probe-based one-step multiplex qRT-PCR assay for rapid identification of avian influenza virus H7N9.
    Zhang, Y. ; Mao, H. ; Yan, J. ; Wang, X. ; Zhang, L. ; Koch, G. ; Li, H. ; Li, Z. ; Chen, Y. ; Gong, L. ; Chen, Z. ; Xia, S. - \ 2014
    Archives of Virology 159 (2014)7. - ISSN 0304-8608 - p. 1707 - 1713.
    infections
    Recently, human deaths have resulted from infection with low-pathogenicity avian influenza virus H7N9 strains that have emerged recently in China. To strengthen H7N9 surveillance and outbreak control, rapid and reliable diagnostic methods are needed. To develop a sensitive quantitative real-time RT-PCR assay for rapid detection of H7N9 viral RNA, primers and AllGlo probes were designed to target the HA and NA genes of H7N9. Conserved sequences in the HA and NA genes were identified by phylogenic analysis and used as targets for H7N9 virus detection. The similarities of the targeted HA and NA gene sequences from different H7 and N9 influenza virus strains were 93.2-99.9 % and 96.0-99.6 %, respectively The specificity and sensitivity of the new multiplex real-time qRT-PCR was established. The test was used for the detection of viral RNA in human pharyngeal swabs and environmental samples. The detection limit of the multiplex qRT-PCR was estimated to be about 10(-1) TCID50/reaction. Finally, the diagnostic sensitivities of the multiplex qRT-PCR, virus isolation and TaqMan qRT-PCR were compared using pharyngeal swabs and environmental samples. These analyses yielded positive results in 46.7 %, 43.3 % and 20.0 % of the samples, respectively. The novel multiplex AllGlo qRT-PCR is a rapid and sensitive method to identify H7N9 virus in clinical and environmental samples and can be used to facilitate studies on the epidemiology of H7N9 virus.
    Plantversterking in potplanten : biostimulanten, middelen en plantreactie in Kalanchoe met Phytophthora, Begonia met Fusarium en Arabidopsis met Phytophthora en Botrytis
    Wurff, A.W.G. van der; Streminska, M.A. ; Slooten, M.A. van; Noort, F.R. van; Holtman, W. ; Korthout, H. - \ 2014
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport / Wageningen UR Glastuinbouw 1326) - 54
    potplanten - stressfactoren - infecties - plantgezondheid - groeiregulatoren - ziekteresistentie - schimmelziekten - landbouwkundig onderzoek - methodologie - glastuinbouw - pot plants - stress factors - infections - plant health - growth regulators - disease resistance - fungal diseases - agricultural research - methodology - greenhouse horticulture
    Potplanten worden tijdens de teelt regelmatig blootgesteld aan stress factoren waarbij ze een verhoogd risico lopen op infecties door schimmels en bacteriën. In deze studie zijn diverse plantversterkers onderzocht.
    Risk factors for persistence of livestock-associated MRSA and environmental exposure in veal calf farmers and their family members: an observational longitudinal study
    Dorado-Garcia, A. ; Bos, M.E.H. ; Graveland, H. ; Cleef, B.A.G.L. van; Verstappen, K.M. ; Kluytmans, J.A.J.W. ; Wagenaar, J.A. ; Heederik, D.J.J. - \ 2013
    BMJ Open 3 (2013)9. - ISSN 2044-6055
    resistant staphylococcus-aureus - animals - carriage - origin - health - st398 - infections - emergence - france - calves
    Objectives: Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) emergence is a major public health concern. This study was aimed at assessing risk factors for persistently carrying MRSA in veal calf farmers and their family members. We also evaluate the dynamics of MRSA environmental load during the veal-calf production cycle. Design: Observational, longitudinal, repeated cross-sectional study. Setting: 52 veal calf farms in the Netherlands. Participants: From the end of 2010 to the end of 2011, a total of 211 farmers, family members and employees were included in the study. Primary outcome and secondary outcome measures: Nasal swabs were taken from participants on days 0, 4, 7 and week 12. A persistent MRSA carrier was defined as a person positive for MRSA on days 0, 4 and 7. Participants filled in an extensive questionnaire to identify potential risk factors and confounders. For estimation of MRSA prevalence in calves and environmental contamination, animal nasal swabs and Electrostatic Dust Collectors were taken on day 0 and week 12. Results: The presence of potential animal reservoirs (free-ranging farm cats and sheep) and the level of contact with veal calves was positively associated with persistent MRSA carriage. Interestingly, at the end of the study (week 12), there was a twofold rise in animal prevalence and a significantly higher MRSA environmental load in the stables was found on farms with MRSA carriers. Conclusions: This study supports the hypothesis that environmental contamination with MRSA plays a role in the acquisition of MRSA in farmers and their household members and suggests that other animal species should also be targeted to implement effective control strategies.
    Betere diagnostiek voor luchtweginfecties bij kalveren
    Klein Haneveld, J. ; Antonis, A.F.G. - \ 2013
    Tijdschrift voor Diergeneeskunde 138 (2013)11. - ISSN 0040-7453 - p. 38 - 41.
    dierziekten - diagnostiek - kalverziekten - kalveren - diergezondheid - ademhalingsziekten - infecties - animal diseases - diagnostics - calf diseases - calves - animal health - respiratory diseases - infections
    Adriaan Antonis werkt dertien jaar bij het Centraal Veterinair Instituut onderdeel van Wageningen UR in Lelystad. Daar wordt onderzoek gedaan naar de bedrijfsgebonden dierziekten, onder andere naar luchtweginfecties op kalverbedrijven. Adriaan werkt mee aan de ontwikkeling van nieuwe diagnostische tests. "Je moet weten wat er op een bedrijf aan de hand is, dan kun je gerichter behandelen".
    Rodent species as natural reservoirs of Borrelia burgdorferi sensu lato in different habitats of Ixodes ricinus in The Netherlands
    Gassner, F. ; Takken, W. ; Plas, C. ; Kastelein, P. ; Hoetmer, A.J. ; Holdinga, M. ; Overbeek, L.S. van - \ 2013
    Ticks and Tick-borne Diseases 4 (2013)5. - ISSN 1877-959X - p. 452 - 458.
    lyme borreliosis - ticks - transmission - association - populations - infections - ehrlichia - ixodidae - forests - acari
    Rodents are natural reservoirs for human pathogenic spirochaetes of the Borrelia burgdorferi complex [B. burgdorferi sensu lato (s.l.)], and the pathogens are transmitted by Ixodes ricinus ticks to humans in The Netherlands. B. burgdorferi s.l. infection prevalence in questing ticks, rodents, and ticks feeding on these rodents, all sampled within the same short time span of five days in three different areas in The Netherlands, were compared in order to establish the relationship between ticks, reservoir hosts, and B. burgdorferi s.l. Questing nymphs were found in all 3 areas and numbers differed per area and even per site within areas. Infection prevalence in questing nymphs ranged between 0 and 20%. Apodemus sylvaticus and Myodes glareolus were the dominant rodents captured, and their numbers differed per area. Infection prevalence, determined by ear biopsies, ranged between 0 and 33.3% for both rodent species. Larvae were most frequently found feeding on these rodents, and their Borrelia infection prevalence ranged between 0 and 6.3% (A. sylvaticus) and between 0 and 29.4% (M. glareolus). The burden of nymphs feeding on rodents was low and varied per area with only 2 of 42 nymphs infected. Comparisons made on the basis of infection prevalence indicated that there was no clear relationship between rodents and questing nymphs when sampled within the same short time span. However, a possible relationship was present when questing ticks were sampled over longer periods in time (months) within or near the same areas (range of infection prevalence between 3.7 and 39.4). Confounding factors thus play a role in the interaction between rodents, ticks, and B. burgdorferi s.l., and it is very likely that other reservoir host species are responsible for the observed fluctuations. It is concluded that the local variations in rodent-Borre/ia-tick interactions only partially explain the Lyme borreliosis risk in the sites studied and that other ecological determinants, notably vertebrate hosts and vegetation structure, should be incorporated in future studies of Lyme borreliosis risk.
    Archaeal virus-host interactions
    Quax, T.E.F. - \ 2013
    Wageningen University. Promotor(en): John van der Oost, co-promotor(en): D. Prangsihvili. - Wageningen : Wageningen UR - ISBN 9789461737830 - 186
    virussen - sulfolobus islandicus rod-shaped virus 2 - archaea - virus-gastheer interacties - infecties - viruses - sulfolobus islandicus rod-shaped virus 2 - archaea - virus-host interactions - infections

    The work presented in this thesis provides novel insights in several aspects of the molecular

    biology of archaea, bacteria and their viruses.

    Three fundamentally different groups of viruses are associated with the three domains of life.

    Archaeal viruses are characterized by a particularly high morphological and genetic diversity. Some

    archaeal viruses, such as Sulfolobus islandicus rod-shaped virus 2 (SIRV2), have quite remarkable

    infection cycles. As described in Chapter 1, infection with SIRV2 results in the formation of

    large virus associated pyramids (VAPs) on the host cell surface. The structures open in the final

    step of the infection cycle, creating large apertures to release the rod-shaped viruses that have

    matured in the cytoplasm. This virus release mechanism is unique and does not resemble egress

    mechanisms of bacterial and eukaryotic viruses. Analysis of the protein composition of SIRV2

    infected cells, as outlined in Chapter 2, revealed the strong accumulation of the virus encoded

    protein PVAP in membranes after infection, suggesting involvement in VAP formation. The

    VAPs can be isolated as discrete particles, as demonstrated in Chapter 3. Electron microscopic

    survey of these particles showed that they are baseless pyramids with a heptagonal perimeter.

    This geometry is exceptional and especially the sevenfold symmetry is very rare in nature

    (20S proteasome, myosin). The structures can have various sizes, probably reflecting different

    developmental stages. This suggests that they grow by the gradual expansion of the triangular

    facets. Analysis of the protein composition of the structures revealed the exclusive presence of

    PVAP and anti-bodies raised against this protein labeled specifically the VAPs on thin sections

    of infected cells as observed in electron microscopy. PVAP is sufficient for VAP formation, which

    was demonstrated by expression of the protein and successful assembly of pyramidal structures,

    in the archaeon S. acidocaldarius and the bacteria Escherichia coli. Further analysis of PVAP

    truncation mutants as outlined in Chapter 4, showed that besides the 10 C-terminal amino

    acids, all domains of the protein are essential for VAP formation. PVAP can form oligomers of

    several sizes, including those of a heptamer, which probably act as nucleation points for VAP

    formation on the cell membrane. Analysis of the truncation mutants indicated that both the C

    and N terminal domain are important for interaction between monomers. Detailed observation

    with whole cell cryo-electron tomography of VAPs formed in the natural and heterologous

    system, revealed the presence of two layers in the structure. The outer one is continuous with

    the cell membrane. The inner layer facing the cytoplasm, presumably represents a protein sheet

    formed by tight interactions between the C-terminal domain of PVAP connected with a short

    linker region to the membrane. The sheets are slightly bended, giving the complete structure the

    appearance of a teepee. At the junction of two triangular sheets, the structure is perforated,

    creating predetermined breaking points. Furthermore, in this chapter data is presented which

    underlines the unique nature of this protein, since it is able to form VAPs successfully in

    archaeal, bacterial and eukaryotic membranes, which all fundamentally differ in protein and

    lipid composition. In case of expression in Saccharomyces cerevisiae, VAPs are formed on all

    membranes, including those of mitochondria, suggesting that the protein inserts spontaneously

    in membranes. Thus, PVAP serves as a universal membrane remodeling system, which might be

    exploited for biotechnological purposes, such as the development into a universal system for the

    controlled opening of ~100 nm apertures in any lipid bilayer.

    Production of VAPs is one of the dramatic consequences that SIRV2 infection has on the

    host cell. Whole transcriptome sequencing allowed determination of a global map of virus

    and host gene expression during the infection cycle, which is presented in Chapter 5. Directly

    after infection, transcription of viral genes starts simultaneously from both genome termini. All

    possible protein interactions between all SIRV2 proteins were assayed with yeast two-hybrid

    and these results were used to advance current knowledge on SIRV2 genes functions, of which

    the majority is still unidentified. The host cells respond to viral infection by adapting expression

    of more than 30% of its genes. Genes involved in cell division are down regulated, while those

    playing a role in anti-viral defense are activated. Specifically, for the first time massive activation

    of toxin anti-toxin and CRISPR-Cas systems is observed in an archaeal system. The different

    degree of expression and activation of the various systems highlights the specialized functions

    they perform.

    The CRISPR-associated multi-subunit ribonucleoprotein complexes that are crucial for the

    CRISPR mediated anti-viral defense, generally have an uneven stoichiometry, i.e. the 4-6 different

    protein subunits are present in different quantities. Just as most functionally related bacterial and

    archaeal genes, the cas genes are clustered in operons, which allow for co-expression (as has

    indeed been observed in the transcriptome analysis described in Chapter 5). This is advantageous

    when equal amounts of gene products are required, such as is the case for protein complexes

    with even stoichiometry. However, a substantial number of important protein complexes

    contain uneven stoichiometry. Employing comparative genomics, in Chapter 6, it is shown

    that differential translation is a key determinant of modulated expression of genes clustered

    in operons and that codon bias generally is the best in silico indicator of unequal protein

    production. In addition, analysis of protein production from genes with synonymous mutations

    from synthetic operons, provides evidence that initiation of translation can occur at intercistronic

    sites. The widespread occurrence of modulation of translation efficiency, suggests that this is

    a universal mode of control in bacteria and archaea that allows for differential production of

    operon-encoded proteins.

    Plasma 25-hydroxyvitamin D concentration and lymphoma risk: results of the European Prospective Investigation into Cancer and Nutrition
    Luczynska, A. ; Kaaks, R. ; Rohrmann, S. ; Becker, S. ; Linseisen, J. ; Buijsse, B. ; Duijnhoven, F.J.B. van - \ 2013
    American Journal of Clinical Nutrition 98 (2013)3. - ISSN 0002-9165 - p. 827 - 838.
    non-hodgkin-lymphoma - chronic lymphocytic-leukemia - vitamin-d status - sun exposure - ultraviolet-radiation - subsequent risk - infections - disease - supplementation - association
    Background: The relation between vitamin D status and lymphoma risk is inconclusive. Objective: We examined the association between prediagnostic plasma 25-hydroxyvitamin D [25(OH)D] and lymphoid cancer risk. Design: We conducted a study nested within the European Prospective Investigation into Cancer and Nutrition cohort of 1127 lymphoma cases and 1127 matched controls with a mean follow-up time of 7.1 y. Conditional logistic regression was used to estimate multivariable-adjusted incidence rate ratios of lymphoma risk in relation to plasma 25(OH)D. Season-standardized and season-specific 25(OH)D quartiles were used. We also analyzed 25(OH)D as a continuous variable and used predefined cutoffs. Results: No statistically significant association between plasma 25(OH)D and overall lymphoid cancer risk was observed. A positive association for B-cell non-Hodgkin lymphoma was noted only in those with a diagnosis made during the first 2 y of follow-up (P-heterogeneity = 0.03), which suggests the possibility of reverse causality. Further analysis restricted to participants with =2 y of follow-up time showed a significant association between 25(OH)D and chronic lymphocytic leukemia (CLL) (n = 161): adjusted incidence rate ratios were 0.40 (95% CI: 0.18, 0.90; P-trend = 0.05) and 0.31 (95% CI: 0.13, 0.76; P-trend = 0.03) for the top compared with the bottom season-standardized and season-specific quartiles, respectively. Data on dietary vitamin D intake provided further support for the observed association (incidence rate ratio: 0.33; 95% CI = 0.12, 0.89; P-trend = 0.006). Conclusions: Our findings do not support a protective role of high 25(OH)D concentration in lymphoid cancers overall. However, they suggest that higher concentrations of 25(OH)D are associated with a reduced risk of CLL.
    Protein transfer to membranes upon shape deformation
    Sagis, L.M.C. ; Bijl, E. ; Antono, L. ; Ruijter, N.C.A. de; Valenberg, H.J.F. van - \ 2013
    The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 61 - 71.
    blood-cell deformability - in-water emulsions - fat globule size - interfacial permeability - flow - drops - milk - dissolution - infections - adsorption
    Red blood cells, milk fat droplets, or liposomes all have interfaces consisting of lipid membranes. These particles show significant shape deformations as a result of flow. Here we show that these shape deformations can induce adsorption of proteins to the membrane. Red blood cell deformability is an important factor in several diseases involving obstructions of the microcirculatory system, and deformation induced protein adsorption will alter the rigidity of their membranes. Deformation induced protein transfer will also affect adsorption of cells onto implant surfaces, and the performance of liposome based controlled release systems. Quantitative models describing this phenomenon in biomaterials do not exist. Using a simple quantitative model, we provide new insight in this phenomenon. We present data that show convincingly that for cells or droplets with diameters upwards of a few micrometers, shape deformations induce adsorption of proteins at their interface even at moderate flow rates.
    Practicalities of using non-local or non-recent multilocus sequence typing data for source attribution in space and time of human campylobacteriosis
    Smid, J.H. ; Gras, L.M. ; Boer, A.G. de; French, N.P. ; Havelaar, A.H. ; Wagenaar, J.A. ; Pelt, W. van - \ 2013
    PLoS ONE 8 (2013)2. - ISSN 1932-6203
    host association - new-zealand - jejuni - genotypes - recombination - switzerland - population - infections - resistance - clones
    In this study, 1208 Campylobacter jejuni and C. coli isolates from humans and 400 isolates from chicken, collected in two separate periods over 12 years in The Netherlands, were typed using multilocus sequence typing (MLST). Statistical evidence was found for a shift of ST frequencies in human isolates over time. The human MLST data were also compared to published data from other countries to determine geographical variation. Because only MLST typed data from chicken, taken from the same time point and spatial location, were available in addition to the human data, MLST datasets for other Campylobacter reservoirs from selected countries were used. The selection was based on the degree of similarity of the human isolates between countries. The main aim of this study was to better understand the consequences of using non-local or non-recent MLST data for attributing domestically acquired human Campylobacter infections to specific sources of origin when applying the asymmetric island model for source attribution. In addition, a power-analysis was done to find the minimum number of source isolates needed to perform source attribution using an asymmetric island model. This study showed that using source data from other countries can have a significant biasing effect on the attribution results so it is important to carefully select data if the available local data lack in quality and/or quantity. Methods aimed at reducing this bias were proposed.
    Detection and Quantification of Leveillula taurica Growth in Pepper Leaves
    Zheng, Z. ; Nonomura, T. ; Bóka, K. ; Matsuda, Y. ; Visser, R.G.F. ; Toyoda, H. ; Kiss, L. ; Bai, Y. - \ 2013
    Phytopathology 103 (2013)6. - ISSN 0031-949X - p. 623 - 632.
    internal transcribed spacer - powdery-mildew - genus leveillula - capsicum-annuum - resistance - pcr - infections - sequences - fungi - dna
    Leveillula taurica is an obligate fungal pathogen that causes powdery mildew disease on a broad range of plants, including important crops such as pepper, tomato, eggplant, onion, cotton, and so on. The early stage of this disease is difficult to diagnose and the disease can easily spread unobserved; for example, in pepper and tomato production fields and greenhouses. The objective of this study was to develop a detection and quantification method of L. taurica biomass in pepper leaves with special regard to the early stages of infection. We monitored the development of the disease to time the infection process on the leaf surface as well as inside the pepper leaves. The initial and final steps of the infection taking place on the leaf surface were consecutively observed using a dissecting microscope and a scanning electron microscope. The development of the intercellular mycelium in the mesophyll was followed by light and transmission electron microscopy. A pair of L. taurica-specific primers was designed based on the internal transcribed spacer sequence of L. taurica and used in real-time polymerase chain reaction (PCR) assay to quantify the fungal DNA during infection. The specificity of this assay was confirmed by testing the primer pair with DNA from host plants and also from another powdery mildew species, Oidium neolycopersici, infecting tomato. A standard curve was obtained for absolute quantification of L. taurica biomass. In addition, we tested a relative quantification method by using a plant gene as reference and the obtained results were compared with the visual disease index scoring. The real-time PCR assay for L. taurica provides a valuable tool for detection and quantification of this pathogen in breeding activities as well in plant-microbe interaction studies.
    Ontwikkeling van praktijktoetsen voor zuur, snot en bolrot
    Vreeburg, P.J.M. ; Doorn, J. van; Dam, M.F.N. van; Gude, H. ; Duijvesteijn, R. ; Pham, K.T.K. ; Kock, M.J.D. de - \ 2013
    Lisse : Praktijkonderzoek Plant en Omgeving BBF - 37
    bloembollen - infecties - erwinia - fusarium - dickeya - testen - methodologie - detectie - snelle methoden - ornamental bulbs - infections - erwinia - fusarium - dickeya - testing - methodology - detection - rapid methods
    Tijdens de handel van bloembollen leiden latente (niet - zichtbare) infecties tot handelsdiscussies en grote verliezen. Om deze handelsdiscussies voor te zijn en verliezen tijdens handel te voorkomen, is het noodzakelijk om latente infecties in een vroeg stadium in de keten te detecteren. Daarom bestaat er behoefte aan een betrouwbare, praktische en vooral snelle toetsmethode om na te kunnen gaan of bepaalde ziekten of ziektekiemen in een partij bloembollen onzichtbaar (latent) aanwezig zijn. Deze toetsmethode is n iet alleen toepasbaar voorafgaand aan de verkoop van partijen. De toetsmethode kan ook ingezet worden gedurende de teelt van plantmateriaal waardoor latent - zieke partijen vroegtijdig herkend kunnen worden, waardoor met passende maatregelen verdere verspreiding van de ziekte voorkomen kan worden.
    Risk Factors for Campylobacteriosis of Chicken, Ruminant, and Environmental Origin: A Combined Case-Control and Source Attribution Analysis
    Gras, L.M. ; Smid, J.H. ; Wagenaar, J.A. ; Boer, A.G. de; Havelaar, A.H. ; Friesema, I.H.M. ; French, N.P. ; Busani, L. ; Pelt, W. van - \ 2012
    PLoS ONE 7 (2012)8. - ISSN 1932-6203
    fragment length polymorphism - disease burden - jejuni clones - new-zealand - netherlands - infections - coli - humans - identification - association
    Background: Campylobacteriosis contributes strongly to the disease burden of food-borne pathogens. Case-control studies are limited in attributing human infections to the different reservoirs because they can only trace back to the points of exposure, which may not point to the original reservoirs because of cross-contamination. Human Campylobacter infections can be attributed to specific reservoirs by estimating the extent of subtype sharing between strains from humans and reservoirs using multilocus sequence typing (MLST). Methodology/Principal Findings: We investigated risk factors for human campylobacteriosis caused by Campylobacter strains attributed to different reservoirs. Sequence types (STs) were determined for 696 C. jejuni and 41 C. coli strains from endemic human cases included in a case-control study. The asymmetric island model, a population genetics approach for modeling Campylobacter evolution and transmission, attributed these cases to four putative animal reservoirs (chicken, cattle, sheep, pig) and to the environment (water, sand, wild birds) considered as a proxy for other unidentified reservoirs. Most cases were attributed to chicken (66%) and cattle (21%), identified as the main reservoirs in The Netherlands. Consuming chicken was a risk factor for campylobacteriosis caused by chicken-associated STs, whereas consuming beef and pork were protective. Risk factors for campylobacteriosis caused by ruminant-associated STs were contact with animals, barbecuing in non-urban areas, consumption of tripe, and never/seldom chicken consumption. Consuming game and swimming in a domestic swimming pool during springtime were risk factors for campylobacteriosis caused by environment-associated STs. Infections with chicken-and ruminant-associated STs were only partially explained by food-borne transmission; direct contact and environmental pathways were also important. Conclusion/Significance: This is the first case-control study in which risk factors for campylobacteriosis are investigated in relation to the attributed reservoirs based on MLST profiles. Combining epidemiological and source attribution data improved campylobacteriosis risk factor identification and characterization, generated hypotheses, and showed that genotype-based source attribution is epidemiologically sensible.
    Inflammation in the middle ear of children with recurrent or chronic otitis media is associated with bacterial load
    Stol, K. ; Diavatopoulos, D.A. ; Graamans, K. ; Engel, J.A. ; Melchers, W.J.G. ; Savelkoul, H.F.J. ; Hays, J.P. ; Warris, A. ; Hermans, P.W.M. - \ 2012
    The Pediatric Infectious Disease Journal 31 (2012)11. - ISSN 0891-3668 - p. 1128 - 1134.
    respiratory-syncytial-virus - real-time pcr - streptococcus-pneumoniae - haemophilus-influenzae - moraxella-catarrhalis - immunoregulatory cytokines - effusion - rhinovirus - infections - expression
    Background: Viral upper respiratory tract infections have been described as an important factor in the development of otitis media (OM), although it is unclear whether they facilitate bacterial OM or can directly cause OM. To clarify the role of viral infections in OM, we compared the relative contribution of viruses and bacteria with the induction of inflammatory cytokine responses in the middle ear of children suffering from OM. Methods: Children up to 5 years of age, with recurrent or chronic episodes of OM and scheduled for ventilation tube insertion were enrolled in a prospective study. Middle ear fluids (n = 116) were collected during surgery, and quantitative polymerase chain reaction was performed to detect bacterial and viral otopathogens, that is, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and 15 respiratory viruses. Finally, concentrations of the inflammatory mediators interleukin (IL)-1 beta, IL-6, IL-8, IL-10, IL-17a and tumor necrosis factor-a were determined. Results: Middle ear fluids were clustered into 4 groups, based on the detection of viruses (28%), bacteria (27%), both bacteria and viruses (27%) or no otopathogens (19%). Bacterial detection was associated with significantly elevated concentrations of cytokines compared with middle ear fluids without bacteria (P <0.001 for all cytokines tested) in a bacterial load-dependent and species-dependent manner. In contrast, the presence of viruses was not associated with changes in cytokine values, and no synergistic effect between viral-bacterial coinfections was observed. Conclusions: The presence of bacteria, but not viruses, is associated with an increased inflammatory response in the middle ear of children with recurrent or chronic OM.
    Livestock-associated MRSA ST398 carriage in pig slaughterhouse workers related to quantitative environmental exposure
    Gilbert, M.J. ; Bos, M.E.H. ; Duim, B. ; Urlings, H.A.P. ; Heres, L. ; Wagenaar, J.A. ; Heederik, D.J.J. - \ 2012
    Occupational and Environmental Medicine 69 (2012)7. - ISSN 1351-0711 - p. 472 - 478.
    resistant staphylococcus-aureus - time pcr assay - methicillin-resistant - high prevalence - netherlands - endocarditis - infections - personnel - bacteria - contact
    Objectives To assess livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) carriage among workers in pig slaughterhouses and assess associated risk factors, including occupational exposure to LA-MRSA. Methods A cross-sectional study in three Dutch pig slaughterhouses was undertaken. Nasal swabs of participants were taken. Nasal swabs and surface wipes, air and glove samples were screened for presence of methicillin-resistant Staphylococcus aureus (MRSA). MRSA was quantitatively determined on gloves and in air samples by culturing and real-time PCR. Results 11 of 341 (3.2%) participants were identified as nasal MRSA carriers. MRSA-positive workers were predominantly found at the start of the slaughter process. Major risk factors for carriage were working in the lairage and working in the scalding and dehairing area. Most nasal isolates (73%) belonged to the LA-MRSA clone ST398. MRSA ST398-positive environmental samples were found throughout the slaughter process. A clear decrease was seen along the slaughterline in the number of MRSA-positive samples and in the MRSA amount per sample. Conclusions This study showed that working in the lairage area or scalding and dehairing area were the major risk factors for MRSA carriage in pig slaughterhouse workers, while the overall prevalence of MRSA carriage is low. Occupational exposure to MRSA decreased along the slaughterline, and the risk of carriage showed a parallel decrease.
    Dietary patterns and respiratory symptoms in pre-school children: The Genreration R Study
    Tromp, I.M. ; Kiefte-de Jong, J.C. ; Vries, J.H.M. de; Jaddoe, V.W. ; Raat, I.J. de; Hofman, M.K. ; Jongste, J.C. de; Moll, H. - \ 2012
    European Respiratory Journal 40 (2012)3. - ISSN 0903-1936 - p. 681 - 689.
    mediterranean diet - spanish schoolchildren - asthma - childhood - pregnancy - atopy - infections - allergies - nutrition - rhinitis
    Overall diet in early childhood may affect the development of respiratory symptoms. This study examined whether childhood dietary patterns are associated with respiratory symptoms in Dutch pre-school children, and whether this association could be explained by energy intake. A prospective cohort study was performed in 2,173 children aged =4 yrs. Data on asthma-related symptoms were obtained by questions from the age-adapted version of the "International Study of Asthma and Allergies in Childhood" questionnaires. Data on respiratory tract infections, defined as episodes of physician attended fever with respiratory symptoms, was obtained by questionnaire. Principal components analysis was used to develop dietary patterns at 14 months of age. Compared with low adherence, high adherence to the “Western” dietary pattern was significantly associated with frequent wheeze at 3 yrs of age (relative risk (RR) 1.39, 95% CI 1.02–1.89) and frequent shortness of breath (RR 1.44, 95% CI 1.03–2.01) and respiratory tract infections (RR 1.54, 95% CI 1.08–2.19) at 4 yrs of age. However, this association was partially explained by energy intake. A “Western” diet may increase the risk of frequent respiratory symptoms at 3 and 4 yrs of age. In some measure, this association was explained by energy intake
    Specific serum antibody responses following a Toxoplasma gondii and Trichinella spiralis co-infection in swine
    Bokken, G. ; Eerden, E. van; Opsteegh, M. ; Augustijn, M. ; Graat, E.A.M. ; Franssen, F. ; Görlich, K. ; Buschtöns, S. ; Tenter, A.M. ; Giessen, J.W.B. van der; Bergwerff, A.A. ; Knapen, F. van - \ 2012
    Veterinary Parasitology 184 (2012)2-4. - ISSN 0304-4017 - p. 126 - 132.
    tissue cysts - pigs - infections - mice - netherlands - diagnosis - britovi - pork
    The aim of this study was to examine the dynamics of parasite specific antibody development in Trichinella spiralis and Toxoplasma gondii co-infections in pigs and to compare these with antibody dynamics in T. spiralis and T. gondii single infections. In this experiment, fiftyfour pigs were divided into five inoculated groups of ten animals, and one control group of four animals. Two groups were inoculated with a single dose of either T. gondii tissue cysts or T. spiralis muscle larvae, one group was inoculated simultaneously with both parasites and two groups were successively inoculated at an interval of four weeks. Specific IgG responses to the parasites were measured by ELISA. T. gondii burden was determined by MC-PCR carried out on heart muscle and T. spiralis burden by artificial digestion of diaphragm samples. Specific IgG responses to T. gondii and T. spiralis in single and simultaneously inoculated animals showed a respective T. gondii and T. spiralis inoculation effect but no significant interaction of these parasites to the development of specific antibodies with the serum dilutions used. Moreover, our data showed that the specific IgG response levels in groups of animals successively or simultaneously co-infected were independent of a respective previous or simultaneous infection with the other parasite. Additionally, no differences in parasite burden were found within groups inoculated with T. gondii and within groups inoculated with T. spiralis. Conclusively, for the infection doses tested in this experiment, the dynamics of specific antibody development does not differ between single and simultaneous or successive infection with T. gondii and T. spiralis. However, lower parasitic doses and other ratios of doses, like low-low, low-high and high-low of T. gondii and T. spiralis in co-infection, in combination with other time intervals between successive infections may have different outcomes and should therefore be studied in further detail.
    Minder groei bij veterinair behandelde varkens
    Peet-Schwering, C.M.C. van der; Binnendijk, G.P. ; Troquet, L.M.P. - \ 2012
    V-focus 9 (2012). - ISSN 1574-1575 - p. 28 - 29.
    varkenshouderij - vleesproductie - varkens - groeisnelheid (slachtvee) - infecties - pig farming - meat production - pigs - liveweight gain - infections
    Vleesvarkens, die gedurende het vleesvarkenstraject een keer veterinair behandeld zijn, groeien van opleg tot afleveren ruim 30 g/d langzamer dan vleesvarkens, die niet veterinair behandeld zijn. Dit geldt zowel voor beren, borgen als zeugjes. Dit blijkt uit onderzoek dat in opdracht van het Productschap Vee en Vlees door Wageningen UR Livestock Research is uitgevoerd op VIC Sterksel.
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