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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    Statistical aspects of food safety sampling
    Jongenburger, I. ; Besten, H.M.W. den; Zwietering, M.H. - \ 2015
    Annual Review of Food Science and Technology 6 (2015). - ISSN 1941-1413 - p. 479 - 503.
    microbiological risk-assessment - escherichia-coli o157 - microbial counts - probable number - salmonella-typhimurium - listeria-monocytogenes - hygienic performances - united-states - distributions - water
    In food safety management, sampling is an important tool for verifying control. Sampling by nature is a stochastic process. However, uncertainty regarding results is made even greater by the uneven distribution of microorganisms in a batch of food. This article reviews statistical aspects of sampling and describes the impact of distributions on the sampling results. Five different batch contamination scenarios are illustrated: a homogeneous batch, a heterogeneous batch with high- or low-level contamination, and a batch with localized high- or low-level contamination. These batch contamination scenarios showed that sampling results have to be interpreted carefully, especially when heterogeneous and localized contamination in food products is expected.
    Prediction of spoilage of tropical shrimp (Penaeus notialis) under dynamic temperature regimes
    Dabade, D.S. ; Azokpota, P. ; Nout, M.J.R. ; Hounhouigan, D.J. ; Zwietering, M.H. ; Besten, H.M.W. den - \ 2015
    International Journal of Food Microbiology 210 (2015). - ISSN 0168-1605 - p. 121 - 130.
    shelf-life prediction - bacterial-growth - sensory characteristics - listeria-monocytogenes - pseudomonas-fragi - microbial model - water activity - packed fish - fresh fish - meat
    The spoilage activity of Pseudomonas psychrophila and Carnobacterium maltaromaticum, two tropical shrimp (Penaeus notialis) spoilage organisms, was assessed in cooked shrimps stored at 0 to 28 °C. Microbiological, chemical and sensory analyses were performed during storage. P. psychrophila had a higher growth rate and showed a higher spoilage activity at temperatures from 0 to 15 °C, while at 28 °C, C. maltaromaticum had a higher growth rate. The spoilage activity of P. psychrophila was found to be higher in cooked shrimp than in fresh shrimp. Observed shelf-life data of shrimps stored at constant temperatures were used to validate a previously developed model that predicts tropical shrimp shelf-life at constant storage temperatures. Models predicting the growth of the spoilage organisms as a function of temperature were constructed. The validation of these models under dynamic storage temperatures simulating temperature fluctuation in the shrimp supply chain showed that they can be used to predict the shelf-life of cooked and fresh tropical shrimps.
    Bacillus cereus ATCC 14579 RpoN (Sigma 54) is a Pleiotropic Regulator of Growth, Carbohydrate, Metabolism, Motility, Biofilm Formation and Toxin Production
    Hayrapetyan, H. ; Tempelaars, M.H. ; Nierop Groot, M.N. ; Abee, T. - \ 2015
    PLoS ONE 10 (2015)8. - ISSN 1932-6203 - 19 p.
    listeria-monocytogenes - escherichia-coli - sigma(54)-dependent genes - transcriptional activator - enterococcus-faecalis - mesentericin y105 - microarray data - pts permease - subtilis - thuringiensis
    Sigma 54 is a transcriptional regulator predicted to play a role in physical interaction of bacteria with their environment, including virulence and biofilm formation. In order to study the role of Sigma 54 in Bacillus cereus, a comparative transcriptome and phenotypic study was performed using B. cereus ATCC 14579 WT, a markerless rpoN deletion mutant, and its complemented strain. The mutant was impaired in many different cellular functions including low temperature and anaerobic growth, carbohydrate metabolism, sporulation and toxin production. Additionally, the mutant showed lack of motility and biofilm formation at air-liquid interphase, and this correlated with absence of flagella, as flagella staining showed only WT and complemented strain to be highly flagellated. Comparative transcriptome analysis of cells harvested at selected time points during growth in aerated and static conditions in BHI revealed large differences in gene expression associated with loss of phenotypes, including significant down regulation of genes in the mutant encoding enzymes involved in degradation of branched chain amino acids, carbohydrate transport and metabolism, flagella synthesis and virulence factors. Our study provides evidence for a pleiotropic role of Sigma 54 in B. cereus supporting its adaptive response and survival in a range of conditions and environments.
    Characterisation of biofilms formed by Lactobacillus plantarum WCFS1 and food spoilage isolates
    Fernández Ramírez, M.D. ; Smid, E.J. ; Abee, T. ; Nierop Groot, M.N. - \ 2015
    International Journal of Food Microbiology 207 (2015). - ISSN 0168-1605 - p. 23 - 29.
    lactic-acid bacteria - enterococcal surface protein - listeria-monocytogenes - pseudomonas-putida - bacillus-subtilis - starter cultures - genetic-analysis - rhamnosus gg - resistance - industry
    Lactobacillus plantarum has been associated with food spoilage in a wide range of products and the biofilm growth mode has been implicated as a possible source of contamination. In this study we analysed the biofilm forming capacity of L. plantarum WCFS1 and six food spoilage isolates. Biofilm formation as quantified by crystal violet staining and colony forming units was largely affected by the medium composition, growth temperature and maturation time and by strain specific features. All strains showed highest biofilm formation in Brain Heart Infusion medium supplemented with manganese and glucose. For L. plantarum biofilms the crystal violet (CV) assay, that is routinely used to quantify total biofilm formation, correlates poorly with the number of culturable cells in the biofilm. This can in part be explained by cell death and lysis resulting in CV stainable material, conceivably extracellular DNA (eDNA), contributing to the extracellular matrix. The strain to strain variation may in part be explained by differences in levels of eDNA, likely as result of differences in lysis behaviour. In line with this, biofilms of all strains tested, except for one spoilage isolate, were sensitive to DNase treatment. In addition, biofilms were highly sensitive to treatment with Proteinase K suggesting a role for proteins and/or proteinaceous material in surface colonisation. This study shows the impact of a range of environmental factors and enzyme treatments on biofilm formation capacity for selected L. plantarum isolates associated with food spoilage, and may provide clues for disinfection strategies in food industry.
    Functional implications of the microbial community structure of undefined mesophilic starter cultures
    Smid, E.J. ; Erkus, O. ; Spus, M. ; Wolkers-Rooijackers, J.C.M. ; Alexeeva, S.V. ; Kleerebezem, M. - \ 2014
    Microbial Cell Factories 13 (2014)suppl. 1. - ISSN 1475-2859
    lactic-acid bacteria - lactococcus-lactis - subsp lactis - listeria-monocytogenes - biovar diacetylactis - metabolic models - cheddar cheese - diversity - cremoris - dairy
    This review describes the recent advances made in the studies of the microbial community of complex and undefined cheese starter cultures. We report on work related to the composition of the cultures at the level of genetic lineages, on the presence and activity of bacteriophages and on the population dynamics during cheese making and during starter culture propagation. Furthermore, the link between starter composition and starter functionality will be discussed. Finally, recent advances in predictive metabolic modelling of the multi-strain cultures will be discussed in the context of microbe-microbe interactions.
    Inactivation of Lactobacillus plantarum WCFS1 during spray drying and storage assessed with complementary viability determination methods
    Perdana, J.A. ; Besten, H.M.W. den; Aryani, D.C. ; Kutahya, O. ; Fox, M.B. ; Kleerebezem, M. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2014
    Food Research International 64 (2014). - ISSN 0963-9969 - p. 212 - 217.
    differential scanning calorimetry - naturally-occurring osmolytes - bacillus-cereus - population heterogeneity - listeria-monocytogenes - thermal inactivation - growth-parameters - stress-response - trehalose - proteins
    Survival of Lactobacillus plantarum WCFS1 spray-dried and stored under different conditions was investigated using complementary methods. One method involved a cell membrane integrity viability-based determination, the other assessed cell growth behavior in a liquid medium by means of detection time or by conventional plating. Survival decreased below 95% when spray drying was carried out at higher outlet spray drying temperatures (Tout N 70 °C). However, the membrane integrity method provided higher residual viability values compared to the detection time and conventional plating. This suggests that loss of viability may be due to a combination of damage to intracellular components and cell membrane. Also during storage viability based on growth behavior declined faster and was more temperature dependent compared to the viability as determined by the membrane integritymethod. Also here additional damage to intracellular components is expected responsible to loss of viability. Major conclusion is that one should not only rely on a cell-membrane integrity based method to assess survival during spray drying and storage of bacteria. Previous studies that did so most probably underestimated viability as critical damage to intracellular components was not assessed.
    Delineating the effect of host environmental signals on a fully virulent strain of Bacillus anthracis using an integrated transcriptomics and proteomics approach
    Panda, G. ; Basak, T. ; Tanwer, P. ; Sengupta, S. ; Martins dos Santos, V.A.P. ; Bhatnagar, R. - \ 2014
    Journal of Proteomics 105 (2014). - ISSN 1874-3919 - p. 242 - 265.
    signature-tagged mutagenesis - listeria-monocytogenes - stationary-phase - iron acquisition - gene-expression - carbon-dioxide - lethal toxin - posttranscriptional regulation - pathogenic bacteria - glycolytic-enzymes
    Pathogenic bacteria sense the host environment and regulate expression of virulence-related genes. Environmental signals like temperature, bicarbonate/CO2 and glucose induce toxin production in Bacillus anthracis, but the mechanisms by which these signals contribute to virulence and overall physiological adaptation remains elusive. An integrated, systems level investigation using transcriptomics and iTRAQ-based proteomics was done to assess the effect of temperature, bicarbonate/CO2 and glucose on B. anthracis. Significant changes observed in amino acid, carbohydrate, energy and nucleotide metabolism indicates events of metabolic readjustments by environmental factors. Directed induction of genes involved in polyamine biosynthesis and iron metabolism revealed the redirection of cellular metabolite pool towards iron uptake. Protein levels of glycolytic enzymes, ptsH and Ldh along with transcripts involved in immune evasion (mprF, bNOS, Phospholipases and asnA), cell surface remodeling (rfbABCD, antABCD, and cls) and utilization of lactate (lutABC) and inositol showed constant repression under environmental perturbations. Discrepancies observed in mRNA/protein level of genes involved in glycolysis, protein synthesis, stress response and nucleotide metabolism hinted at the existence of additional regulatory layers and illustrated the utility of an integrated approach. The above findings might assist in the identification of novel adaptive strategies of B. anthracis during host associated survival and pathogenesis.
    Cultivated strains of Agaricus bisporus and A.brasiliensis: chemical characterization and evaluation of antioxidant and antimicrobial properties for the final healthy product – natural preservatives in yoghurt
    Stojkovic, D.S. ; Reis, F.S. ; Glamoclija, J. ; Ciric, A. ; Barros, L. ; Griensven, L.J.L.D. van; Ferreira, I.C.F.R. ; Sokovic, M. - \ 2014
    Food & Function 5 (2014)7. - ISSN 2042-6496 - p. 1602 - 1612.
    mushroom basidiomycetes extracts - fatty-acid-composition - in-vitro antioxidant - edible mushrooms - nutritional-value - wild mushrooms - listeria-monocytogenes - button mushrooms - uv-irradiation - ergosterol
    Agaricus bisporus (J. E. Lange) Emil J. Imbach and Agaricus brasiliensis Wasser, M. Didukh, Amazonas & Stamets are edible mushrooms. We chemically characterized these mushrooms for nutritional value, hydrophilic and lipophilic compounds. The antioxidant and antimicrobial activities of methanolic and ethanolic extracts were assessed. Hepatotoxicity was also evaluated. The ethanolic extract of both species was tested for inhibition of Listeria monocytogenes growth in yoghurt. Both species proved to be a good source of bioactive compounds. A. brasiliensis was richer in polyunsaturated fatty acids and revealed the highest concentration of phenolic acids, and tocopherols. A. bisporus showed the highest monounsaturated fatty acids and ergosterol contents. A. brasiliensis revealed the highest antioxidant potential, and its ethanolic extract displayed the highest antibacterial potential; the methanolic extract of A. bisporus revealed the highest antifungal activity. A. brasiliensis possessed better preserving properties in yoghurt.
    Challenges in Performance of Food Safety Management Systems: A Case of Fish Processing Companies in Tanzania
    Kussaga, J.B. ; Luning, P.A. ; Tiisekwa, B.P.M. ; Jacxsens, L. - \ 2014
    Journal of Food Protection 77 (2014)4. - ISSN 0362-028X - p. 621 - 630.
    listeria-monocytogenes - quality - plants - haccp - standards - industry - exports - output - model - chain
    This study provides insight for food safety (FS) performance in light of the current performance of core FS management system (FSMS) activities and context riskiness of these systems to identify the opportunities for improvement of the FSMS. A FSMS diagnostic instrument was applied to assess the performance levels of FSMS activities regarding context riskiness and FS performance in 14 fish processing companies in Tanzania. Two clusters (cluster I and II) with average FSMS (level 2) operating under moderate-risk context (score 2) were identified. Overall, cluster I had better (score 3) FS performance than cluster II (score 2 to 3). However, a majority of the fish companies need further improvement of their FSMS and reduction of context riskiness to assure good FS performance. The FSMS activity levels could be improved through hygienic design of equipment and facilities, strict raw material control, proper follow-up of critical control point analysis, developing specific sanitation procedures and company-specific sampling design and measuring plans, independent validation of preventive measures, and establishing comprehensive documentation and record-keeping systems. The risk level of the context could be reduced through automation of production processes (such as filleting, packaging, and sanitation) to restrict people’s interference, recruitment of permanent highskilled technological staff, and setting requirements on product use (storage and distribution conditions) on customers. However, such intervention measures for improvement could be taken in phases, starting with less expensive ones (such as sanitation procedures) that can be implemented in the short term to more expensive interventions (setting up assurance activities) to be adopted in the long term. These measures are essential for fish processing companies to move toward FSMS that are more effective.
    Pulsed electric field processing of different fruit juices: impac of pH and temperature on inactivation of spoilage and pathogenic micro-organisms
    Timmermans, R.A.H. ; Nierop Groot, M.N. ; Nederhoff, A.L. ; Boekel, M.A.J.S. van; Matser, A.M. ; Mastwijk, H.C. - \ 2014
    International Journal of Food Microbiology 173 (2014). - ISSN 0168-1605 - p. 105 - 111.
    escherichia-coli o157-h7 - listeria-monocytogenes - orange juice - saccharomyces-cerevisiae - apple juice - lactobacillus-plantarum - salmonella-typhimurium - modeling inactivation - thermal inactivation - mild pasteurization
    Pulsed electrical field (PEF) technology can be used for the inactivation of micro-organisms and therefore for preservation of food products. It is a mild technology compared to thermal pasteurization because a lower temperature is used during processing, leading to a better retention of the quality. In this study, pathogenic and spoilage micro-organisms relevant in refrigerated fruit juices were studied to determine the impact of process parameters and juice composition on the effectiveness of the PEF process to inactivate the micro-organisms. Experiments were performed using a continuous-flow PEF system at an electrical field strength of 20kV/cm with variable frequencies to evaluate the inactivation of Salmonella Panama, Escherichia coli, Listeria monocytogenes and Saccharomyces cerevisiae in apple, orange and watermelon juices. Kinetic data showed that under the same conditions, S. cerevisiae was the most sensitive micro-organism, followed by S. Panama and E. coli, which displayed comparable inactivation kinetics. L. monocytogenes was the most resistant micro-organism towards the treatment conditions tested. A synergistic effect between temperature and electric pulses was observed at inlet temperatures above 35°C, hence less energy for inactivation was required at higher temperatures. Different juice matrices resulted in a different degree of inactivation, predominantly determined by pH. The survival curves were nonlinear and could satisfactorily be modeled with the Weibull model.
    The Antimicrobial Activity of the Essential Oil of Pistacia lentiscus var. Chia
    Gkogka, E. ; Hazeleger, W.C. ; Posthumus, M.A. ; Beumer, R.R. - \ 2013
    Journal of Essential Oil Bearing Plants 16 (2013)6. - ISSN 0972-060X - p. 714 - 729.
    plant essential oils - tea tree oil - escherichia-coli o157-h7 - helicobacter-pylori - mastic gum - listeria-monocytogenes - chemical-composition - in-vitro - antibacterial activity - staphylococcus-aureus
    The essential oil of the resin of Pistacia lentiscus var. Chia (mastic oil) was studied in vitro against a wide range of foodborne pathogenic and spoilage microorganisms with a diffusion and a dilution method. Furthermore its chemical composition was analyzed by means of Gas Chromatography-Mass Spectrometry (GC-MS) and the possibility of using the essential oil in food preservation was discussed. The Minimal Inhibitory Concentrations (MICs) of mastic oil were estimated for 6 species of bacteria (Bacillus cereus, Campylobacter jejuni, Clostridium perfringens, Escherichia coli, Salmonella Typhimurium, Staphylococcus aureus), 2 species of yeasts (Saccharomyces cerevisiae and Zygosaccharomyces bailii) and 3 species of fungi (Penicillium roquefortii, Aspergillus flavus and Eurotium amstelodami). GC-MS analysis revealed a chemotype dominated by monoterpenes, principally alpha-pinene and beta-myrcene comprising more than 90 % of the mastic oil. Both methods showed Cl. perfringens as the most susceptible microorganism followed by S. cerevisiae and Z. bailii. With the exception of C. jejuni, Gram-positive were found to be more susceptible to the essential oil than Gram-negative microorganisms and all fungi appeared very resistant to mastic oil. Based on the observed MICs, the contribution of mastic oil to the preservation of bakery/confectionary products at the amounts currently used for flavoring purposes is likely to be negligible.
    A multiplex bead-based suspension array assay for interrogation of phylogenetically informative single nucleotide polymorphisms for Bacillus anthracis
    Thierry, S. ; Hamidjaja, R.A. ; Girault, G. ; Lofstrom, C. ; Ruuls-van Stalle, E.M.F. ; Sylviane, D. - \ 2013
    Journal of Microbiological Methods 95 (2013)3. - ISSN 0167-7012 - p. 357 - 365.
    tandem-repeat analysis - large-scale - listeria-monocytogenes - pathogen detection - genotyping assays - dna - probes - discrimination - amplification - pcr
    Single nucleotide polymorphisms (SNPs) are abundant in genomes of all species and represent informative DNA markers extensively used to analyze phylogenetic relationships between strains. Medium to high throughput, open methodologies able to test many SNPs in a minimum time are therefore in great need. By using the versatile Luminex (R) xTAG technology, we developed an efficient multiplexed SNP genotyping assay to score 13 phylogenetically informative SNPs within the genome of Bacillus anthracis. The Multiplex Oligonucleotide Ligation-PCR procedure (MOL-PCR) described by Deshpande et al., 2010 has been modified and adapted for simultaneous interrogation of 13 biallelic canonical SNPs in a 13-plex assay. Changes made to the originally published method include the design of allele-specific dual-priming-oligonucleotides (DPOs) as competing detection probes (MOLigo probes) and use of asymmetric PCR reaction for signal amplification and labeling of ligation products carrying SNP targets. These innovations significantly reduce cross-reactivity observed when initial MOLigo probes were used and enhance hybridization efficiency onto the microsphere array, respectively. When evaluated on 73 representative samples, the 13-plex assay yielded unambiguous SNP calls and lineage affiliation. Assay limit of detection was determined to be 2 ng of genomic DNA. The reproducibility, robustness and easy-of-use of the present method were validated by a small-scale proficiency testing performed between four European laboratories. While cost-effective compared to other singleplex methods, the present MOL-PCR method offers a high degree of flexibility and scalability. It can easily accommodate newly identified SNPs to increase resolving power to the canSNP typing of B. anthracis. (C) 2013 Elsevier B.V. All rights reserved.
    Risk assessment strategies as a tool in the application of the Appropriate Level of Protection (ALOP) and Food Safety Objective (FSO) by risk managers
    Gkogka, E. ; Reij, M.W. ; Gorris, L.G.M. ; Zwietering, M.H. - \ 2013
    International Journal of Food Microbiology 167 (2013)1. - ISSN 0168-1605 - p. 8 - 28.
    salmonella-typhimurium dt104 - bacterial cross-contamination - broiler supply chain - minced pork meat - listeria-monocytogenes - thermal inactivation - foodborne pathogens - escherichia-coli - assessment model - bacillus-cereus
    In the course of the last decade, the Appropriate Level of Protection (ALOP), the Food Safety Objective (FSO) and their associated metrics have been proposed by the World Trade Organization and Codex Alimentarius as a means for competent authorities to ultimately translate governmental public health policy regarding food safety into risk-based targets for the food industry. The industry needs to meet these targets through the effective choice of control measures that are part of its operational food safety management system. The aim of this study was to put the practical application of ALOP and FSO to the test in the case of Salmonella in chicken meat in the Netherlands. Two different risk assessment approaches were applied to derive potential ALOP and FSO values, a ‘top-down’ approach based on epidemiological data and a ‘bottom-up’ approach based on food supply chain data. To this end, two stochastic models specific to the Dutch situation were built. Comparisons between 23 countries in Europe were also made using the top-down model. The mean estimated current Level Of Protection values were similar for the two approaches applied, with the bottom-up model yielding 87 cases per 100,000 inhabitants per year (95% CI: 0.03, 904) and the top-down model 71 (95% CI: 9.9, 155). The estimated FSO values on the other hand were considerably different with the mean ‘top down’ FSO being - 4.6 log CFU/g (95% CI: - 5.4, - 4.1) and the mean ‘bottom-up’ FSO - 6.0 log CFU/g (95% CI: - 8.1, - 2.9) reflecting major differences in the output distributions of this parameter obtained with the two approaches. Significant differences were observed between current LOP values for different EU countries, although it was not clear whether this was due to actual differences in the factors influencing the risk of salmonellosis or due to the quality of the available data. Keywords Risk assessment; Stochastic modelling; Salmonellosis; Foodborne disease; Public health targets
    Towards a decision support system for control of multiple food safety hazards in raw milk production
    Spiegel, M. van der; Sterrenburg, P. ; Haasnoot, W. ; Fels-Klerx, H.J. van der - \ 2013
    Trends in Food Science and Technology 34 (2013)2. - ISSN 0924-2244 - p. 137 - 145.
    listeria-monocytogenes - antibiotic-residues - control charts - biosensors - pathogen - feed - consumption - management - chain - risk
    Decision support systems (DSS) for controlling multiple food safety hazards in raw milk production have not yet been developed, but the underlying components are fragmentarily available. This article presents the state-of-the-art of essential DSS elements for judging food safety compliance of raw milk. The DSS elements include data identification at critical points in the supply chain, an information management system, and data exchange. Based on these elements, a concept for further development of a DSS is presented. These elements have to be integrated in the dairy chain to prevent inefficient sampling and analysis. Such a DSS would enhance food safety.
    Transcriptome signatures of class I and III stress response deregulation in Lactobacillus plantarum reveal pleiotropic adaptation
    Bokhorst-van de Veen, H. van; Bongers, R.S. ; Wels, M. ; Bron, P.A. ; Kleerebezem, M. - \ 2013
    Microbial Cell Factories 12 (2013)1. - ISSN 1475-2859 - 15 p.
    gram-positive bacteria - heat-shock response - lactic-acid bacteria - bacillus-subtilis - listeria-monocytogenes - gastrointestinal-tract - low gc - streptococcus-pneumoniae - comparative genomics - helicobacter-pylori
    Background - To cope with environmental challenges bacteria possess sophisticated defense mechanisms that involve stress-induced adaptive responses. The canonical stress regulators CtsR and HrcA play a central role in the adaptations to a plethora of stresses in a variety of organisms. Here, we determined the CtsR and HrcA regulons of the lactic acid bacterium Lactobacillus plantarum WCFS1 grown under reference (28°C) and elevated (40°C) temperatures, using ctsR, hrcA, and ctsR-hrcA deletion mutants. Results - While the maximum specific growth rates of the mutants and the parental strain were similar at both temperatures (0.33¿±¿0.02 h-1 and 0.34¿±¿0.03 h-1, respectively), DNA microarray analyses revealed that the CtsR or HrcA deficient strains displayed altered transcription patterns of genes encoding functions involved in transport and binding of sugars and other compounds, primary metabolism, transcription regulation, capsular polysaccharide biosynthesis, as well as fatty acid metabolism. These transcriptional signatures enabled the refinement of the gene repertoire that is directly or indirectly controlled by CtsR and HrcA of L. plantarum. Deletion of both regulators, elicited transcriptional changes of a large variety of additional genes in a temperature-dependent manner, including genes encoding functions involved in cell-envelope remodeling. Moreover, phenotypic assays revealed that both transcription regulators contribute to regulation of resistance to hydrogen peroxide stress. The integration of these results allowed the reconstruction of CtsR and HrcA regulatory networks in L. plantarum, highlighting the significant intertwinement of class I and III stress regulons. Conclusions - Taken together, our results enabled the refinement of the CtsR and HrcA regulatory networks in L. plantarum, illustrating the complex nature of adaptive stress responses in this bacterium
    Comparative genomic analysis of twelve Streptococcus suis (pro)phages
    Tang, F. ; Bossers, A. ; Harders, F.L. ; Lu, C. ; Smith, H.E. - \ 2013
    Genomics 101 (2013)6. - ISSN 0888-7543 - p. 336 - 344.
    listeria-monocytogenes - serotype 14 - bacteriophage - phage - protein - sequence - strains - integration - virulence - system
    Streptococcus suis (S. suis) is an important pathogen that can carry prophages. Here we present a comparative genomic analysis of twelve (pro)phages identified in the genomes of S. suis isolates. According to the putative functions of the open reading frames predicted, all genomes could be organized into five major functionally gene clusters involved in lysogeny, replication, packaging, morphogenesis and lysis. Phylogenetic analyses of the prophage sequences revealed that the prophages could be divided into five main groups. Whereas the genome content of the prophages in groups 1, 2 and 3 showed quite some similarity, the genome structures of prophages in groups 4 and 5 were quite distinct. Interestingly, several genes homologous to known virulence factors, including virulence associated protein E, a toxin-antitoxin system, a Clp protease and a DNA methyltransferase were found to be associated with various (pro)phages. This clearly indicates that these (pro)phages can contribute to the virulence of their hosts.
    O-glycosylation as a novel control mechanism of peptidoglycan hydrolase activity
    Rolain, T. ; Bernard, E. ; Beaussart, A. ; Degand, H. ; Courtin, P. ; Egge-Jacobsen, W. ; Bron, P.A. ; Morsomme, P. ; Kleerebezem, M. ; Chapot-Chartier, M.P. ; Dufrêne, Y.F. ; Hols, P. - \ 2013
    Journal of Biological Chemistry 288 (2013)31. - ISSN 0021-9258 - p. 22233 - 22247.
    lactobacillus-plantarum wcfs1 - diamino acid endopeptidase - lactococcus-lactis - teichoic-acids - staphylococcus-aureus - cell-separation - bacterial-peptidoglycan - n-acetylglucosaminidase - listeria-monocytogenes - protein glycosylation
    Acm2, the major autolysin of Lactobacillus plantarum, is a tripartite protein. Its catalytic domain is surrounded by an O-glycosylated N-terminal region rich in Ala, Ser, and Thr (AST domain), which is of low complexity and unknown function, and a C-terminal region composed of five SH3b peptidoglycan (PG) binding domains. Here, we investigate the contribution of these two accessory domains and of O-glycosylation to Acm2 functionality. We demonstrate that Acm2 is an N-acetylglucosaminidase and identify the pattern of O-glycosylation (21 mono-N-acetylglucosamines) of its AST domain. The O-glycosylation process is species-specific as Acm2 purified from Lactococcus lactis is not glycosylated. We therefore explored the functional role of O-glycosylation by purifying different truncated versions of Acm2 that were either glycosylated or non-glycosylated. We show that SH3b domains are able to bind PG and are responsible for Acm2 targeting to the septum of dividing cells, whereas the AST domain and its O-glycosylation are not involved in this process. Notably, our data reveal that the lack of O-glycosylation of the AST domain significantly increases Acm2 enzymatic activity, whereas removal of SH3b PG binding domains dramatically reduces this activity. Based on this antagonistic role, we propose a model in which access of the Acm2 catalytic domain to its substrate may be hindered by the AST domain where O-glycosylation changes its conformation and/or mediates interdomain interactions. To the best of our knowledge, this is the first time that O-glycosylation is shown to control the activity of a bacterial enzyme.
    Modeling the impact of the indigenous microbial population on the maximum population density of Salmonella on alfalfa
    Rijgersberg, H. ; Nierop Groot, M.N. ; Tromp, S.O. ; Franz, E. - \ 2013
    World Journal of Microbiology and Biotechnology 29 (2013)7. - ISSN 0959-3993 - p. 1301 - 1305.
    escherichia-coli o157-h7 - listeria-monocytogenes - predictive microbiology - ground-beef - growth - temperature - survival - sprouts - storage - microflora
    Within a microbial risk assessment framework, modeling the maximum population density (MPD) of a pathogenic microorganism is important but often not considered. This paper describes a model predicting the MPD of Salmonella on alfalfa as a function of the initial contamination level, the total count of the indigenous microbial population, the maximum pathogen growth rate and the maximum population density of the indigenous microbial population. The model is parameterized by experimental data describing growth of Salmonella on sprouting alfalfa seeds at inoculum size, native microbial load and Pseudomonas fluorescens 2–79. The obtained model fits well to the experimental data, with standard errors less than ten percent of the fitted average values. The results show that the MPD of Salmonella is not only dictated by performance characteristics of Salmonella but depends on the characteristics of the indigenous microbial population like total number of cells and its growth rate. The model can improve the predictions of microbiological growth in quantitative microbial risk assessments. Using this model, the effects of preventive measures to reduce pathogenic load and a concurrent effect on the background population can be better evaluated. If competing microorganisms are more sensitive to a particular decontamination method, a pathogenic microorganism may grow faster and reach a higher level. More knowledge regarding the effect of the indigenous microbial population (size, diversity, composition) of food products on pathogen dynamics is needed in order to make adequate predictions of pathogen dynamics on various food products.
    Surface behaviour of S. Thyphimurium, S. Derby, S. Brandenburg and S. Infantis
    Castelijn, G.A.A. ; Parabirsing, J.A. ; Zwietering, M.H. ; Moezelaar, R. ; Abee, T. - \ 2013
    Veterinary Microbiology 161 (2013)3-4. - ISSN 0378-1135 - p. 305 - 314.
    enterica serovar typhimurium - food contact surfaces - biofilm-formation - listeria-monocytogenes - salmonella spp. - foodborne pathogens - cross-contamination - escherichia-coli - stainless-steel - feed factories
    Cross-contamination due to Salmonella on the surface of processing equipment greatly contributes to contamination of pork products. Therefore, a clear understanding of surface and survival behaviour of relevant Salmonella serovars in pork processing environments is needed to develop better strategies for Salmonella control. Within this study the biofilm forming behaviour of S. Typhimurium, S. Derby, S. Brandenburg and S. Infantis isolates was analysed using the crystal violet assay. This assay, commonly used to analyse total biofilm formation, revealed variation in biofilm forming capacity between and within serovars. This has not been shown before for S. Derby, S. Brandenburg and S. Infantis. From each serovar, isolates with different biofilm forming capacity were selected to analyse biofilm formation on stainless steel. This revealed no significant differences between biofilm formation on polystyrene compared to stainless steel. Furthermore a relation was observed between biofilm forming capacity of an isolate and survival on stainless steel surfaces. On such surfaces, biofilms showed greater and longer survival than planktonic cells, and they were less susceptible to peracetic acid disinfection treatments. However, the latter effect was marginal and only observed in the presence of organic material, which drastically decreased the activity of peracetic acid. With the obtained results a hierarchical cluster was also performed to identify differences and similarities between the four different serovars. This indicated that the surface behaviour of S. Typhimurium was more comparable to S. Infantis than to S. Derby or S. Brandenburg
    Catalase activity as a biomarker for mild-stress-induced robustness in Bacillus weihenstephanensis
    Besten, H.M.W. den; Effraimidou, S. ; Abee, T. - \ 2013
    Applied and Environmental Microbiology 79 (2013)1. - ISSN 0099-2240 - p. 57 - 62.
    atcc 14579 cells - listeria-monocytogenes - environmental-changes - adaptive response - oxidative stress - acid tolerance - salt stress - cereus - temperature - resistance
    Microorganisms are able to survive and grow in changing environments by activating stress adaptation mechanisms which may enhance bacterial robustness. Stress-induced enhanced robustness complicates the predictability of microbial inactivation. Using psychrotolerant Bacillus weihenstephanensis strain KBAB4 as a model, we investigated the impact of the culturing temperature on mild-oxidative-stress-induced (cross-)protection toward multiple stresses, including severe oxidative, heat, and acid stresses. Culturing at a refrigeration temperature (7°C) compared to the optimal growth temperature (30°C) affected both the robustness level of B. weihenstephanensis and the oxidative stress adaptive response. Scavengers of reactive oxygen species have a crucial role in adaptation to oxidative stresses, and this points to a possible predictive role in mild-oxidative-stress-induced robustness. Therefore, the catalase activity was determined upon mild oxidative stress treatment and was demonstrated to be significantly correlated with the robustness level of mild-stress-treated cells toward severe oxidative and heat stresses but not toward severe acid stress for cells grown at both refrigeration and optimal temperatures. The quantified correlations supported the predictive quality of catalase activity as a biomarker and also underlined that the predictive quality is stress specific. Biomarkers that are able to predict stress-induced enhanced robustness can be used to better understand stress adaptation mechanisms and might allow the design of effective combinations of hurdles to control microbial behavior
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