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Staff Publications

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

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Latest developments on Streptococcus suis: an emerging zoonotic pathogen: part 1
Segura, M. ; Zheng, H. ; Greeff, A. de; Gao, G.F. ; Grenier, D. ; Jiang, Y. ; Chengping, L. ; Maskell, D. ; Oishi, K. ; Okura, M. ; Osawa, R. ; Schultsz, C. ; Schwerk, C. ; Sekizaki, T. ; Smith, H. ; Srimanote, P. ; Takamatsu, D. ; Tang, J. ; Tenenbaum, T. ; Tharavichitkul, P. ; Hoa, N.T. ; Valentin-Weigand, P. ; Wells, J.M. ; Wertheim, H. ; Zhu, B. ; Xu, J. ; Gottschalk, M. - \ 2014
Future Microbiology 9 (2014)4. - ISSN 1746-0913 - p. 441 - 444.
serotype-2 - thailand - infection - diversity
The first international workshop on Streptococcus suis, which is an important swine pathogen and emerging zoonotic agent, took place in Beijing, jointly organized by the Faculty of Veterinary Medicine, University of Montreal, Canada and the National Institute for Communicable Disease Control and Prevention, China CDC. The aim of the meeting was to gather together, for the first time, more than 80 researchers working on S. suis, from countries including China, Canada, Japan, The Netherlands, Germany, Thailand, the UK and Vietnam. This article, the first of a two-part report on this First International Workshop, reviews current aspects of the epidemiology and population genomics of S. suis, covers public health concerns and discusses questions about S. suis serotyping and molecular diagnostics.
Transmission of Actinobacillus pleuropneumoniae among weaned piglets on endemically infected farms
Tobias, T.J. ; Bouma, A. ; Broek, J. van den; Nes, A. van; Daemen, A.J.J.M. ; Wagenaar, J.A. ; Stegeman, J.A. ; Klinkenberg, D. - \ 2014
Preventive Veterinary Medicine 117 (2014)1. - ISSN 0167-5877 - p. 207 - 214.
between-pen transmission - acquired colostral antibodies - within-pen - airborne transmission - pigs - serotype-2 - virus - herd - quantification - colonization
Clinical outbreaks due to Actinobacillus pleuropneumoniae occur recurrently, despite the wide-scale use of antimicrobials or vaccination. Therefore, new approaches for the prevention and control of these outbreaks are necessary. For the development of alternative measures, more insight into the transmission of the bacterium on farms is necessary. The aim of this cohort study was to quantify transmission of A. pleuropneumoniae amongst weaned piglets on farms. We investigated three possible transmission routes: (i) indirect transmission by infected piglets within the same compartment, (ii) transmission by infected pigs in adjacent pens and (iii) transmission by direct contact within pens. Additionally, we evaluated the effect of independent litter characteristics on the probability of infection. Two farms participated in our study. Serum and tonsil brush samples were collected from sows pre-farrowing. Serum was analysed for antibodies against Apx toxins and Omp. Subsequently, tonsil brush samples were collected from all piglets from these dams (N = 542) in three cohorts, 3 days before weaning and 6 weeks later. Tonsil samples were analysed by qPCR for the presence of the apxIVA gene of A. pleuropneumoniae. Before weaning, 25% of the piglets tested positive; 6 weeks later 47% tested positive. Regression and stochastic transmission models were used to assess the contribution of each of the three transmission routes and to estimate transmission rates. Transmission between piglets in adjacent pens did not differ significantly from that between non-adjacent pens. The transmission rate across pens was estimated to be 0.0058 day(-1) (95% CI: 0.0030-0.010), whereas the transmission rate within pens was ten times higher 0.059 day(-1) (95% CI: 0.048-0.072). Subsequently, the effects of parity and serological response of the dam and litter age at weaning on the probability of infection of pigs were evaluated by including these into the regression model. A higher dam ApxII antibody level was associated with a lower probability of infection of the pig after weaning; age at weaning was associated with a higher probability of infection of the pig after weaning. Finally, transmission rate estimates were used in a scenario study in which the litters within a compartment were mixed across pens at weaning instead of raising litter mates together in a pen. The results showed that the proportion of infected piglets increased to 69% if litters were mixed at weaning, indicating that farm management measures may affect spread of A. pleuropneumoniae. (C) 2014 Elsevier B.V. All rights reserved.
A cohort study on Actinobacillus pleuropneumoniae colonisation in suckling piglets
Tobias, T.J. ; Klinkenberg, D. ; Bouma, A. ; Broek, J. van den; Daemen, A.J.J.M. ; Wagenaar, J.A. ; Stegeman, J.A. - \ 2014
Preventive Veterinary Medicine 114 (2014)3-4. - ISSN 0167-5877 - p. 223 - 230.
infection patterns - pigs - antibodies - transmission - efficacy - herds - sows - serotype-2 - hemolysin - vaccine
Actinobacillus pleuropneumoniae causes respiratory disease in pigs and despite the use of preventive measures such as vaccination and antimicrobials clinical outbreaks still occur. At weaning often many piglets are not colonised. If differences in prevalence between litters are large and if factors were known that could explain these differences, this may provide an opportunity to raise groups of A. pleuropneumoniae free piglets. To this end, a cohort study was performed on two endemically infected farrow-to-finish farms. Seventy-six of 133 sows were selected using stratified random selection by parity. Farmers complied with a strict hygiene and animal management protocol to prevent transmission between litters. Tonsil brush and serum samples taken three weeks before parturition were tested for antigen with an apxIVA qPCR and antibodies with Apx and Omp ELISAs, respectively. Three days before weaning tonsil brush samples from all piglets (n = 871) were collected and tested for antigen. Whereas all sows tested positive both in serology tests as well as qPCR, 0.41 of the litters tested fully negative and 0.73 of all piglets tested negative. The proportion of positively tested piglets in positive litters ranged from 0.08-1.0 (median= 0.36). A grouped logistic regression model with a beta binomial distribution of the probability for piglets to become infected was fitted to the data and associations with explanatory variables were explored. To test the possibility that alternatively the clustering was caused by onwards transmission among the piglets, a transmission model was fitted to the data incorporating sow-piglet and piglet-piglet transmission, but this model did not fit better. The results of this study showed that the number of colonised suckling piglets was highly clustered and mainly attributable to the variability of infectiousness of the dam, but no dam related risk factor for colonisation status of litter or piglets within litters could be identified. (C) 2014 Elsevier B.V. All rights reserved.
A naturally occurring nucleotide polymorphism in the orf2/folc promoter is associated with Streptococcus suis virulence
Greeff, A. de; Buys, H. ; Wells, J.M. ; Smith, H.E. - \ 2014
BMC Microbiology 14 (2014)1. - ISSN 1471-2180
germ-free pigs - serotype-2 - strains - identification - cytokine - pathogen - suilysin - release - type-2 - cells
Streptococcus suis is a major problem in the swine industry causing meningitis, arthritis and pericarditis in piglets. Pathogenesis of S. suis is poorly understood. We previously showed that introduction of a 3 kb genomic fragment from virulent serotype 2 strain 10 into a weakly virulent serotype 2 strain S735, generated a hypervirulent isolate. The 3 kb genomic fragment contained two complete open reading frames (ORF) in an operon-structure of which one ORF showed similarity to folylpolyglutamate synthetase, whereas the function of the second ORF could not be predicted based on database searches for protein similarity.
Latest developments on Streptococcus suis: an emerging zoonotic pathogen: part 2
Segura, M. ; Zheng, H. ; Greeff, A. de; Gao, G.F. ; Gremier, D. ; Jiang, Y. ; Chengping, L. ; Maskell, D. ; Oishi, K. ; Okura, M. ; Osawa, R. ; Schultsz, C. ; Schwerk, C. ; Sekizaki, T. ; Smith, H. ; Srimanote, P. ; Takamatsu, D. ; Tang, J. ; Tenenbaum, T. ; Tharavichitkul, P. ; Hoa, N.T. ; Valentin-Weigand, P. ; Wells, J.M. ; Wertheim, H. ; Zhu, B. ; Xu, J. ; Gottschalk, M. - \ 2014
Future Microbiology 9 (2014)5. - ISSN 1746-0913 - p. 587 - 591.
cerebrospinal fluid barrier - plexus epithelial-cells - in-vitro - bacterial interactions - swine pathogen - serotype-2 - infection - diversity - virulence - release
This second and final chapter of the report on the First International Workshop on Streptococcus suis follows on from Part 1, published in the April 2014, volume 9, issue 4 of Future Microbiology. S. suis is a swine pathogen and a zoonotic agent afflicting people in close contact with infected pigs or pork meat. Although sporadic cases of human infections had been reported worldwide, deadly S. suis outbreaks emerged in Asia. The severity of the disease underscores the lack of knowledge on the virulence and zoonotic evolution of this human-infecting agent. The pathogenesis of the infection, interactions with host cells and new avenues for treatments were among the topics discussed during the First International Workshop on S. suis (China 2013).
Detection of Actinobacillus pleuropneumoniae in pigs by real-time quantitative PCR for the apxIVA gene
Tobias, T.J. ; Bouma, A. ; Klinkenberg, D. ; Daemen, A.J.J.M. ; Stegeman, J.A. ; Wagenaar, J.A. ; Duim, B. - \ 2012
The Veterinary Journal 193 (2012)2. - ISSN 1090-0233 - p. 557 - 560.
multiplex pcr - identification - assay - transmission - serotype-2
A real-time quantitative PCR (qPCR) for detection of the apxIVA gene of Actinobacillus pleuropneumoniae was validated using pure cultures of A. pleuropneumoniae and tonsillar and nasal swabs from experimentally inoculated Caesarean-derived/colostrum-deprived piglets and naturally infected conventional pigs. The analytical sensitivity was 5 colony forming units/reaction. In comparison with selective bacterial examination using tonsillar samples from inoculated animals, the diagnostic sensitivity of the qPCR was 0.98 and the diagnostic specificity was 1.0. The qPCR showed consistent results in repeatedly sampled conventional pigs. Tonsillar brush samples and apxIVA qPCR analysis may be useful for further epidemiological studies and monitoring for A. pleuropneumoniae.
Immunomodulatory effects of streptococcus suis capsule type on human dendritic cell responses, phagocytosis and intracellular survival.
Meijerink, M. ; Ferrando, M.L. ; Lammers, G. ; Taverne, N. ; Smith, H.E. ; Wells, J. - \ 2012
PLoS One 7 (2012)4. - ISSN 1932-6203
in-vivo - zoonotic pathogen - genetic diversity - dc-sign - group-b - virulence - serotype-2 - pigs - polysaccharide - strains
Streptococcus suis is a major porcine pathogen of significant commercial importance worldwide and an emerging zoonotic pathogen of humans. Given the important sentinel role of mucosal dendritic cells and their importance in induction of T cell responses we investigated the effect of different S. suis serotype strains and an isogenic capsule mutant of serotype 2 on the maturation, activation and expression of IL-10, IL-12p70 and TNF-a in human monocyte-derived dendritic cells. Additionally, we compared phagocytosis levels and bacterial survival after internalization. The capsule of serotype 2, the most common serotype associated with infection in humans and pigs, was highly anti-phagocytic and modulated the IL-10/IL-12 and IL-10/TNF-a cytokine production in favor of a more anti-inflammatory profile compared to other serotypes. This may have consequences for the induction of effective immunity to S. suis serotype 2 in humans. A shielding effect of the capsule on innate Toll-like receptor signaling was also demonstrated. Furthermore, we showed that 24 h after phagocytosis, significant numbers of viable intracellular S. suis were still present intracellularly. This may contribute to the dissemination of S. suis in the body.
Genetic diversity of Streptococcus suis isolates as determined by comparative genome hybridization
Greeff, A. de; Wisselink, H.J. ; Bree, F.M. de; Schultsz, C. ; Baums, C.G. ; Ngo Thi, Hoa ; Stockhofe-Zurwieden, N. ; Smith, H.E. - \ 2011
BMC Microbiology 11 (2011). - ISSN 1471-2180 - 15 p.
germ-free pigs - hyaluronate lyase - capsular type-2 - binding protein - virulence - identification - serotype-2 - strains - expression - purification
Background Streptococcus suis is a zoonotic pathogen that causes infections in young piglets. S. suis is a heterogeneous species. Thirty-three different capsular serotypes have been described, that differ in virulence between as well as within serotypes.Results In this study, the correlation between gene content, serotype, phenotype and virulence among 55 S. suis strains was studied using Comparative Genome Hybridization (CGH). Clustering of CGH data divided S. suis isolates into two clusters, A and B. Cluster A isolates could be discriminated from cluster B isolates based on the protein expression of extracellular factor (EF). Cluster A contained serotype 1 and 2 isolates that were correlated with virulence. Cluster B mainly contained serotype 7 and 9 isolates. Genetic similarity was observed between serotype 7 and serotype 2 isolates that do not express muramidase released protein (MRP) and EF (MRP-EF-), suggesting these isolates originated from a common founder. Profiles of 25 putative virulence-associated genes of S. suis were determined among the 55 isolates. Presence of all 25 genes was shown for cluster A isolates, whereas cluster B isolates lacked one or more putative virulence genes. Divergence of S. suis isolates was further studied based on the presence of 39 regions of difference. Conservation of genes was evaluated by the definition of a core genome that contained 78% of all ORFs in P1/7.Conclusions In conclusion, we show that CGH is a valuable method to study distribution of genes or gene clusters among isolates in detail, yielding information on genetic similarity, and virulence traits of S. suis isolates.
TroA of Streptococcus suis is required for manganese acquisition and full virulence
Wichgers Schreur, P.J. ; Rebel, J.M.J. ; Smits, M.A. ; Putten, J.P.M. van; Smith, H.E. - \ 2011
Journal of Bacteriology 193 (2011)19. - ISSN 0021-9193 - p. 5073 - 5080.
pneumococcal surface-antigen - 7 european countries - crystal-structure - diseased pigs - pneumoniae - protein - serotype-2 - infection - vaccine - iron
Streptococcus suis causes infections in pigs and occasionally in humans resulting in 23 manifestations as meningitis, sepsis, arthritis and septic shock. For survival within the 24 host, S. suis requires numerous nutrients including trace metals. Little is known about 25 the specific proteins involved in metal scavenging in S. suis. In this study we evaluated 26 the role of the putative high affinity metal binding lipoprotein TroA in metal acquisition 27 and virulence. A mutant strain deficient in the expression of TroA (¿troA mutant) was 28 constructed. Growth of the ¿troA mutant in Todd-Hewitt broth was similar to wild type 29 growth, however growth of the ¿troA mutant in cation-deprived Todd-Hewitt broth and 30 in porcine serum was strongly reduced compared to growth of wild type bacteria. 31 Supplementing the media with extra manganese but not with magnesium, zinc, copper, 32 nickel or iron restored growth to wild type levels, indicating that TroA is specifically 33 required for growth in environments low in manganese. The ¿troA mutant also showed 34 increased susceptibility to H2O2, suggesting TroA is involved in counteracting oxidative 35 stress. Furthermore, the expression of the troA gene was subject to environmental 36 regulation at the transcript level. In a murine S. suis infection model the ¿troA mutant 37 displayed a non-virulent phenotype. These data indicate that S. suis TroA is involved in 38 manganese acquisition and required for full virulence in mice.
Lgt processing is an essential step in Streptococcus suis lipoprotein mediated innate immune activation
Wichgers, P.J. ; Rebel, J.M.J. ; Smits, M.A. ; Putten, J.P. van; Smith, H.E. - \ 2011
PLoS One 6 (2011)7. - ISSN 1932-6203
bacterial lipoproteins - lipid modification - virulence - serotype-2 - identification - pneumoniae - proteins - type-2 - prelipoproteins - polysaccharide
Background Streptococcus suis causes invasive infections in pigs and occasionally in humans. The host innate immune system plays a major role in counteracting S. suis infections. The main components of S. suis able to activate the innate immune system likely include cell wall constituents that may be released during growth or after cell wall integrity loss, however characterization of these components is still limited. Methology/Principal Findings A concentrated very potent innate immunity activating supernatant of penicillin-treated S. suis was SDS-PAGE fractionated and tested for porcine peripheral blood mononucleated cell (PBMC) stimulating activity using cytokine gene transcript analysis. More than half of the 24 tested fractions increased IL-1ß and IL-8 cytokine gene transcript levels in porcine PBMCs. Mass spectrometry of the active fractions indicated 24 proteins including 9 lipoproteins. Genetic inactivation of a putative prolipoprotein diacylglyceryl transferase (Lgt) gene resulted in deficient lipoprotein synthesis as evidenced by palmitate labeling. The Lgt mutant showed strongly reduced activation of porcine PBMCs, indicating that lipoproteins are dominant porcine PBMC activating molecules of S. suis. Conclusion/Significance This study for the first time identifies and characterizes lipoproteins of S. suis as major activators of the innate immune system of the pig. In addition, we provide evidence that Lgt processing of lipoproteins is required for lipoprotein mediated innate immune activation
Involvement of NF-¿B and MAP-kinases in the transcriptional response of alveolar macrophages to Streptococcus suis
Greeff, A. de; Benga, A. ; Wichgers, P.J. ; Valentin-Weigand, P. ; Rebel, J.M.J. ; Smith, H.E. - \ 2010
Veterinary Microbiology 141 (2010)1-2. - ISSN 0378-1135 - p. 59 - 67.
bacterial pathogens - murine macrophages - immune-response - capsular type-2 - identification - recognition - expression - serotype-2 - monocytes - infection
Interaction of Streptococcus suis with primary porcine alveolar macrophages was Studied using transcriptomics. Transcriptional response of macrophages to two different S. suis strains was studied: wild-type S10 that is resistant to phagocytosis, and its non-encapsulated mutant that is phagocytosed efficiently. The macrophages' transcriptional response was observed only after 60 min of incubation. Eleven genes were expressed significantly different between macrophages infected with streptococci and control mock-infected macrophages. These genes include IL-1-beta, MIP-2-alpha and TNF-alpha. When gene expression was studied as a function of time, transcriptional changes occurred in all macrophages independent of streptococci. The fold induction of induced genes however, was much stronger in macrophages incubated with the non-encapsulated S. suis strain that was phagocytosed. The genes that were higher induced due to S. suis suggest an innate immune response is induced in macrophages. Pathway analysis revealed that genes that are part of the putative MAP-kinase signal transduction system are over-represented among the regulated genes. Using an immortalized alveolar macrophage cell line it was shown that macrophages respond to interaction with S. suis by the translocation of NF-kappa B to the nucleus, independent of phagocytosis. This translocation subsequently induced expression of innate immune genes. This strongly suggests besides the MAP-kinase signaling pathway, NF-kappa B signaling is also induced upon interaction with S. suis. (C) 2009 Elsevier B.V. All rights reserved.
A wind density model to quantify the airborne spread of culicoides species
Hendrickx, G. ; Gilbert, M. ; Staubach, C. ; Elbers, A.R.W. ; Mintiens, K. ; Gerbier, G. ; Ducheyne, E. - \ 2008
Preventive Veterinary Medicine 87 (2008)1-2. - ISSN 0167-5877 - p. 162 - 181.
possible windborne spread - mouth-disease virus - united-kingdom - air streams - vectors - ceratopogonidae - identification - diptera - surveillance - serotype-2
Increased transport and trade as well as climate shifts play an important role in the introduction, establishment and spread of new pathogens. Arguably, the introduction of bluetongue virus (BTV) serotype 8 in Benelux, Germany and France in 2006 is such an example. After its establishment in receptive local vector and host populations the continued spread of such a disease in a suitable environment will mainly depend on movement of infected vectors and animals. In this paper we explore how wind models can contribute to explain the spread of BTV in a temperate eco-climatic setting. Based on previous work in Greece and Bulgaria filtered wind density maps were computed using data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Six hourly forward wind trajectories were computed at pressure levels of 850 hPa for each infected farm as from the recorded onset of symptoms. The trajectories were filtered to remove wind events that do not contribute to possible spread of the vector. The suitable wind events were rastered and aggregated on a weekly basis to obtain weekly wind density maps. Next to this, cumulated wind density maps were also calculated to assess the overall impact of wind dispersal of vectors. A strong positive correlation was established between wind density data and the horizontal asymmetrical spread pattern of the 2006 BTV8 epidemic. It was shown that short (31 km) distance spread had a different impact on disease spread. Computed wind densities were linked to the medium/long-distance spread whilst short range spread was mainly driven by active Culicoides flight. Whilst previous work in the Mediterranean basin showed that wind driven spread of Culicoides over sea occurred over distances of up to 700 km, this phenomenon was not observed over land. Long-distance spread over land followed a hopping pattern, i.e. with intermediary stops and establishment of local virus circulation clusters at distances of 35¿85 km. Despite suitable wind densities, no long range spread was recorded over distances of 300¿400 km. Factors preventing spread Eastwards to the UK and Northwards to Denmark during the 2006 epidemic are discussed. Towards the east both elevation and terrain roughness, causing air turbulences and drop down of Culicoides, were major factors restricting spread. It is concluded that the proposed approach opens new avenues for understanding the spread of vector-borne viruses in Europe. Future developments should take into consideration both physical and biological factors affecting spread.
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