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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    Differential outgrowth potential of Clostridium perfringens food-borne isolates with various cpe-genotypes in vacuum-packed ground beef during storage at 12°C
    Xiao, Y. ; Wagendorp, A. ; Abee, T. ; Wells-Bennik, M.H.J. - \ 2015
    International Journal of Food Microbiology 194 (2015). - ISSN 0168-1605 - p. 40 - 45.
    enterotoxin gene - multiplex pcr - heat-resistance - cooked beef - a strains - plasmid - growth - spores - sporulation - expression
    In the current study, the outgrowth of spores of 15 different food isolates of Clostridium perfringens was evaluated in vacuum-packed ground beef during storage at 12 °C and 25 °C. This included enterotoxic strains carrying the gene encoding the CPE enterotoxin on the chromosome (C-cpe), on a plasmid (P-cpe) and cpe-negative strains. The 15 strains were selected from a larger group of strains that were first evaluated for their ability to sporulate in modified Duncan–Strong sporulating medium. Sporulation ability varied greatly between strains but was not associated with a particular cpe genotype. In line with previous studies, the tested C-cpe strains produced spores with significantly higher heat resistance than the cpe-negative and P-cpe strains (both IS1151 and IS1470-like) with the exception of strain VWA009. Following inoculation of vacuum-packed cooked ground beef with spores, the heat-resistant C-cpe strains showed lower outgrowth potential in this model food stored at 12 °C than the P-cpe and cpe-negative strains, while no significant differences were observed at 25 °C. These results suggest that the latter strains may have a competitive advantage over C-cpe strains at reduced temperatures during storage of foods that support the growth of C. perfringens. While spores of P-cpe strains are readily inactivated by heat processing, post-processing contamination by food handlers who may carry P-cpe strains that have a better growth potential at lower temperatures must be avoided. The varying responses of C. perfringens spores to heat and the differences in outgrowth capacity at different temperatures are factors to be considered in strain selection for challenge tests, and for predictive modelling of C. perfringens.
    Abiotic and microbiotic factors controlling biofilm formation by thermophilic sporeformers
    Zhao, Y. ; Caspers, M.P.M. ; Metselaar, K.I. ; Boer, P. de; Roeselers, G. ; Moezelaar, R. ; Nierop Groot, M.N. ; Montijn, R.C. ; Abee, T. ; Kort, R. - \ 2013
    Applied and Environmental Microbiology 79 (2013)18. - ISSN 0099-2240 - p. 5652 - 5660.
    bacterial communities - raw-milk - spores - identification - diversity
    One of the major concerns in the production of dairy concentrates is the risk of contamination by heat-resistant spores from thermophilic bacteria. In order to acquire more insight in the composition of microbial communities occurring in the dairy concentrate industry, a bar-coded 16S amplicon sequencing analysis was carried out on milk, final products, and fouling samples taken from dairy concentrate production lines. The analysis of these samples revealed the presence of DNA from a broad range of bacterial taxa, including a majority of mesophiles and a minority of (thermophilic) spore-forming bacteria. Enrichments of fouling samples at 55°C showed the accumulation of predominantly Brevibacillus and Bacillus, whereas enrichments at 65°C led to the accumulation of Anoxybacillus and Geobacillus species. Bacterial population analysis of biofilms grown using fouling samples as an inoculum indicated that both Anoxybacillus and Geobacillus preferentially form biofilms on surfaces at air-liquid interfaces rather than on submerged surfaces. Three of the most potent biofilm-forming strains isolated from the dairy factory industrial samples, including Geobacillus thermoglucosidans, Geobacillus stearothermophilus, and Anoxybacillus flavithermus, have been characterized in detail with respect to their growth conditions and spore resistance. Strikingly, Geobacillus thermoglucosidans, which forms the most thermostable spores of these three species, is not able to grow in dairy intermediates as a pure culture but appears to be dependent for growth on other spoilage organisms present, probably as a result of their proteolytic activity. These results underscore the importance of abiotic and microbiotic factors in niche colonization in dairy factories, where the presence of thermophilic sporeformers can affect the quality of end products.
    A mixed-species microarray for identification of food spoilage bacilli
    Caspers, M.P.M. ; Schuren, F.H.J. ; Zuijlen, A.C.M. van; Brul, S. ; Montijn, R.C. ; Abee, T. ; Kort, R. - \ 2011
    Food Microbiology 28 (2011)2. - ISSN 0740-0020 - p. 245 - 251.
    subtilis - spores - heat - resistance - diversity - genomics - cereus
    Failure of food preservation is frequently caused by thermostable spores of members of the Bacillaceae family, which show a wide spectrum of resistance to cleaning and preservation treatments. We constructed and validated a mixed-species genotyping array for 6 Bacillus species, including Bacillus subtilis, Bacillus licheniformis, Bacillus pumilus, Bacillus sporothermodurans, Bacillus cereus and Bacillus coagulans, and 4 Geobacillus species, including Geobacillus stearothermophilus, Geobacillus thermocatenulatus, Geobacillus toebii and Geobacillus sp., in order to track food spoilage isolates from ingredient to product. The discriminating power of the array was evaluated with sets of 42 reference and 20 test strains. Bacterial isolates contain a within-species-conserved core genome comprising 68–88% of the entire genome and a non-conserved accessory genome comprising 7–22%. The majority of the core genome markers do not hybridise between species, thus they allow for efficient discrimination at the species level. The accessory genome array markers provide high-resolution discrimination at the level of individual isolates from a single species. In conclusion, the reported mixed-species microarray contains discriminating markers that allow rapid and cost-effective typing of Bacillus food spoilage bacteria in a wide variety of food products. Keywords: Bacillus; Geobacillus; Genotyping; Comparative genome hybridisation; Microarray; Tracking and tracing; Food spoilage; Bacterial spores
    Modelling: One word for many activities and uses
    Zwietering, M.H. ; Besten, H.M.W. den - \ 2011
    Food Microbiology 28 (2011)4. - ISSN 0740-0020 - p. 818 - 822.
    bacillus-cereus - predictive microbiology - atcc-14579 - stress - spores
    Modelling in food microbiology relies on the development and use of mathematical equations to describe biological processes. These models can be used to perform various tasks from quantitatively describing a phenomenon, testing significant kinetic differences, quantitatively investigate mechanisms and correlations, designing experiments and sampling plans, or predicting phenomena within a food chain to enable optimal control. It is important to clearly identify what one wants to realize, and depending on the purpose of the model, select the most appropriate approach for modelling. In this paper various applications are illustrated and for each application an example is given to highlight the broad use of models and model results in food microbiology
    Temperature uniformity mapping in a high pressure high temperature reactor using a temperature sensitive indicator
    Grauwet, T. ; Plancken, I. van der; Vervoort, L. ; Matser, A.M. ; Hendrickx, M. ; Loey, A. van - \ 2011
    Journal of Food Engineering 105 (2011)1. - ISSN 0260-8774 - p. 36 - 47.
    inactivation kinetics - elevated-temperatures - numerical-simulation - enzyme inactivation - sterilization - spores - food - ionization - texture - quality
    Recently, the first prototype ovomucoid-based pressure–temperature–time indicator (pTTI) for high pressure high temperature (HPHT) processing was described. However, for temperature uniformity mapping of high pressure (HP) vessels under HPHT sterilization conditions, this prototype needs to be optimized. To this end, this work aimed at the development of an ovomucoid-based indicator with combined pressure temperature dependent inactivation kinetics and a sufficient pressure temperature stability relevant for commercial HPHT sterilization. After varying buffer type and the pH at ambient pressure and temperature (pHi), an indicator based on 1 g/L ovomucoid in 0.1 M MES-NaOH buffer pHi 6.2 was selected. The inactivation behavior of this indicator system is characterized by pressure temperature dependent (combined Arrhenius–Eyring) first-order kinetics in the processing domain relevant for HPHT sterilization. This indicator showed good integrating properties under isobaric–isothermal and dynamic pressure temperature conditions. In a temperature uniformity study of a vertically oriented, pilot-scale HPHT vessel, pTTI readouts at different coordinates illustrated low and high temperature zones. As the inactivation of spores under HPHT is clearly positively temperature dependent, the food safety objective has to be verified in the former sampling zone.
    Process audits versus product quality monitoring of bulk milk
    Velthuis, A.G.J. ; Asseldonk, M.A.P.M. van - \ 2011
    Journal of Dairy Science 94 (2011)7. - ISSN 0022-0302 - p. 235 - 249.
    butyric-acid bacteria - somatic-cell count - farm tank milk - assurance program - bacteriological quality - management-practices - recall costs - risk-factors - dairy - spores
    The aim was to investigate whether on-line somatic cell count (SCC) assessment, when combined with electrical conductivity (EC), should be implemented at the udder quarter or at the cow level. Data were collected from 3 farms with automatic milking systems, resulting in 3,191 quarter milkings used in the analyses. Visual observations of foremilk and quarter milk samples for laboratory SCC analysis were used to define 2 gold standards. One was based on visual observation only and the other was based on a combination of visual observation and SCC (using a reference value of 500,000 cells/mL), which means that a quarter milking must have visually abnormal milk as well as an increased SCC to be categorized positive. On-line SCC assessment took place at the quarter level during the first part of the milking. Composite cow level samples were used for laboratory SCC analysis and to compare the performance of SCC assessment at quarter and cow levels. The EC at the quarter level was measured by in-line sensors of the automatic milking system. Alerts for SCC indicators were calculated based on straightforward reference values. Alerts for EC were based on straightforward reference values, or on interquarter ratios. The latter was calculated by dividing the value of a given quarter by the average value of the 2 lowest quarters of that milking. The EC and SCC indicators were combined with either a Boolean “and” or “or” function. Receiver operating characteristic curves were used to visually present results using different threshold values. Sensitivity, specificity, and success rate at the quarter level and false alert rate per 1,000 cow milkings were used to compare indicators at given sensitivity or specificity levels. Quarter level SCC assessment was superior to cow level assessment (transformed partial area under the curve = 0.70 vs. 0.62) when combined with EC measurement at quarter level. When aiming for the same sensitivity level (e.g., 50%) with all visual abnormal milk as the gold standard, more false alerts were generated with cow level assessment (137 per 1,000 cow milkings) compared with quarter level SCC assessment (75 per 1,000 cow milkings). As a comparison, using EC alone resulted in 292 false alerts per 1,000 cow milkings in the same situation. Therefore, it is concluded that quarter level SCC assessment was superior to cow level assessment when combined with EC measurement at quarter level. Key words: abnormal milk; detection; on-line assessment; somatic cell count
    Water- and air-distributed conidia differ in sterol content and cytoplasmic microviscosity
    Leeuwen, M.R. van; Doorn, T.M. van; Golovina, E.A. ; Stark, J. ; Dijksterhuis, J. - \ 2010
    Applied and Environmental Microbiology 76 (2010)1. - ISSN 0099-2240 - p. 366 - 369.
    penicillium-discolor - germinating conidia - plasma-membrane - ergosterol - viscosity - radicals - filipin - spores
    Airborne and waterborne fungal spores were compared with respect to cytoplasmic viscosity and the presence of ergosterol. These parameters differed markedly between the two spore types and correlated with spore survival. This suggests that the mode of spore dispersal has a bearing on cellular composition, which is relevant for the eradication of industrially relevant fungal propagules
    Effect van vruchtwisseling op Helminthosporium aantasting in maïs : pottenproef 2009
    Meier, R. ; Schepers, H.T.A.M. ; Schooten, H.A. van - \ 2009
    Lelystad : Praktijkonderzoek Plant & Omgeving, Sector AGV (PPO rapport ) - 17
    bladvlekkenziekte - helminthosporium - rotaties - maïs - maïskuilvoer - sporen - leaf spotting - helminthosporium - rotations - maize - maize silage - spores
    Bladvlekkenziekte in maïs veroorzaakt door de schimmel Helminthosporium spp., kwam tot voor kort nauwelijks voor in Nederland. In meer zuidelijke Europese landen, zoals Zuid-Duitsland, Oostenrijk en Frankrijk heerst de ziekte al langer. Schade in snijmaïs kan door massale aantasting aanzienlijk zijn wat tot uiting komt in lagere opbrengsten en lagere voederwaarde. Voor de korrelmaïs en ccm-telers betekent een aantasting reductie van de korrelopbrengst en mogelijk hogere droogkosten als gevolg van een negatief effect op het droge stof gehalte van de korrels. Een aantasting kan ook consequenties hebben voor het inkuilen en de bewaarbaarheid van snijmaïs. In 2009 is oriënterend onderzoek gestart naar het effect van vruchtwisseling op Helminthosporium aantasting. Hiertoe is in 2009 grond verzameld van maïspercelen waar in 2007 en/of 2008 maïs heeft gestaan die was aangetast door Helminthosporium. In een pottenproef is getest of er in deze grond levensvatbare sporen aanwezig waren die maïs konden aantasten.
    Modelling the number of viable vegetative cells of Bacillus cereus passing through the stomach
    Wijnands, L.M. ; Pielaat, A. ; Dufrenne, J.B. ; Zwietering, M.H. ; Leusden, F.M. van - \ 2009
    Journal of Applied Microbiology 106 (2009)1. - ISSN 1364-5072 - p. 258 - 267.
    acid tolerance response - gastrointestinal transit - hemolysin bl - low-ph - healthy - prevalence - strains - growth - spores - foods
    Aims: Model the number of viable vegetative cells of B. cereus surviving the gastric passage after experiments in simulated gastric conditions. Materials and Methods: The inactivation of stationary and exponential phase vegetative cells of twelve different strains of Bacillus cereus, both mesophilic and psychrotrophic strains isolated from food and faeces from healthy and ill individuals, in simulated gastric conditions was determined using decimal reduction times at low pH (DpH). Subsequently inactivation rates were calculated. Inclusion of the inactivation rates into models describing the course of the gastric pH after the consumption of meal of solid food and the transfer of food from the stomach to the small intestine resulted in numbers of viable Bacillus cereus vegetative cells able to pass the stomach. Conclusions: According to the model, 3¿26% of the ingested vegetative cells from Bacillus cereus may survive the gastric passage, dependent on the growth phase of the vegetative cells, the type of strains, and the age of the consumer. Significance and Impact of the Study: Vegetative cells of Bacillus cereus may be involved in the onset of diarrhoeal disease to a greater extent than expected since up to 26% of the ingested cells survive simulated gastric conditions.
    Role of germinant receptors in Caco-2 cell-initiated germination of Bacillus cereus ATCC 14579 endospores
    Hornstra, L.M. ; Voort, M. van der; Wijnands, L.M. ; Roubos-van den Hil, P.J. ; Abee, T. - \ 2009
    Applied and Environmental Microbiology 75 (2009). - ISSN 0099-2240 - p. 1201 - 1203.
    atcc-14579 - spores - differentiation - expression - toxins
    Spores obtained from Bacillus cereus ATCC 14579 and mutant strains lacking each of seven germinant receptor operons were exposed to differentiated Caco-2 cells and monitored for germination. Spores of the gerI and gerL mutants showed a reduced germination response, pointing to a role for these receptors in Caco-2- induced germination.
    Overwintering van zwartvruchtrot
    Jong, P.F. de; Heijne, B. - \ 2007
    Randwijk : PPO sector Fruit (PPO rapport nr. 2007-20) - 31
    pyrus communis - peren - stemphylium vesicarium - plantenziekteverwekkende schimmels - hibernatie - sporen - infecties - nederland - pyrus communis - pears - stemphylium vesicarium - plant pathogenic fungi - hibernation - spores - infections - netherlands
    Zwartvruchtrot wordt veroorzaakt door de schimmel Stemphylium vesicarium. De geslachtelijke vorm is Pleospora allii. De schade die de ziekte kan veroorzaken is groot. Dit heeft tot gevolg dat de telers veel spuiten omdat ze hun gewas ziektevrij willen houden.
    Short communication: quantification of the transmission of microorganisms to milk via dirt attached to the exterior of teats
    Vissers, M.M.M. ; Driehuis, F. ; Giffel, M.C.T. ; Jong, P. de; Lankveld, J.M.G. - \ 2007
    Journal of Dairy Science 90 (2007)8. - ISSN 0022-0302 - p. 3579 - 3582.
    butyric-acid bacteria - farm tank milk - raw-milk - risk-assessment - spores - contamination
    Pathogens and spoilage microorganisms can be transmitted to milk via dirt (e.g., feces, bedding material, soil, or a combination of these) attached to the exterior of the cows¿ teats. To determine the relevance of this pathway and to perform quantitative microbial risk analysis of the microbial contamination of farm tank milk (FTM), it is important to know the amount of dirt transmitted to milk via the exterior of teats. In this study at 11 randomly selected Dutch farms the amount of dirt transmitted to milk via the exterior of teats is determined using spores of mesophilic aerobic bacteria as a marker for transmitted dirt. The amount of transmitted dirt to milk varied among farms from 3 to 300 mg/L, with an average of 59 mg/L. The usefulness of the data for microbial risk analyses is briefly illustrated using the contamination of FTM with spores of butyric acid bacteria as a case study. In a similar way the data can be used to identify measures to control the contamination of FTM with other microorganisms or chemical residues.
    Stemphy uitgebouwd met sporulatiemodel
    Jong, P.F. de; Boshuizen, A. - \ 2007
    De Fruitteelt 97 (2007)8. - ISSN 0016-2302 - p. 18 - 19.
    gewasbescherming - fruitteelt - peren - stemphylium vesicarium - plantenziekteverwekkende schimmels - schimmelbestrijding - fungiciden - sporulatie - sporen - modellen - plant protection - fruit growing - pears - stemphylium vesicarium - plant pathogenic fungi - fungus control - fungicides - sporulation - spores - models
    In 2006 is voor het eerst het sporulatiemodel van Stemphy voor zwartvruchtrot beproefd. Daarbij is gekeken of dit model de sporenvluchten goed voorspelde en of een bestrijding op basis van het model een gewenst resultaat op zou leveren. De eerste bevindingen zijn zeer hoopvol. Op verschillende plaatsen is ervaring opgedaan met het waarschuwingsmodel Stemphy van Bodata in de bestrijding van zwartvruchtrot. In 2006 is het eerste onderdeel hiervan, het infectiemodel, voor gebruik in de praktijk beschikbaar. Dit model wordt meegeleverd met het Mety-programma, dat door meer dan 150 fruittelers wordt gebruikt. De ervaringen met het Stemphy-model in de praktijk zijn positief
    Air-liquid interface biofilms of Bacillus cereus: formation, sporulation, and dispersion
    Wijman, J.G.E. ; Leeuw, P.P.L.A. de; Moezelaar, R. ; Zwietering, M.H. ; Abee, T. - \ 2007
    Applied and Environmental Microbiology 73 (2007)5. - ISSN 0099-2240 - p. 1481 - 1488.
    oneidensis mr-1 biofilms - listeria-monocytogenes - pseudomonas-aeruginosa - bacterial biofilms - stainless-steel - genome sequence - di-gmp - subtilis - detachment - spores
    Biofilm formation by Bacillus cereus was assessed using 56 strains of B. cereus, including the two sequenced strains, ATCC 14579 and ATCC 10987. Biofilm production in microtiter plates was found to be strongly dependent on incubation time, temperature, and medium, as well as the strain used, with some strains showing biofilm formation within 24 h and subsequent dispersion within the next 24 h. A selection of strains was used for quantitative analysis of biofilm formation on stainless steel coupons. Thick biofilms of B. cereus developed at the air-liquid interface, while the amount of biofilm formed was much lower in submerged systems. This suggests that B. cereus biofilms may develop particularly in industrial storage and piping systems that are partly filled during operation or where residual liquid has remained after a production cycle. Moreover, depending on the strain and culture conditions, spores constituted up to 90% of the total biofilm counts. This indicates that B. cereus biofilms can act as a nidus for spore formation and subsequently can release their spores into food production environments
    Improving farm management by modeling the contamination of farm tank milk with butyric acid bacteria
    Vissers, M.M.M. ; Driehuis, F. ; Giffel, M.C. te; Jong, P. de; Lankveld, J.M.G. - \ 2006
    Journal of Dairy Science 89 (2006)3. - ISSN 0022-0302 - p. 850 - 858.
    clostridium-tyrobutyricum - bacillus-cereus - grass-silage - cheese - growth - spores - food
    Control of contamination of farm tank milk (FTM) with the spore-forming butyric acid bacteria (BAB) is important to prevent the late-blowing defect in semi-hard cheeses. The risk of late blowing can be decreased via control of the contamination level of FTM with BAB. A modeling approach was applied to identify an effective control strategy at the farm level. The simulation model developed was based on a translation of the contamination pathway into a chain of unit operations. Using various simulations, the effects of factors related to feed quality, feed management, cattlehouse hygiene, and milking practices on the contamination level of FTM were evaluated. Contamination level of silage was found to be the most important factor. When silage contains on average less than 3 log(10) BAB/g, a basic pretreatment of udder teats before milking (similar to 75% removal of attached spores) is sufficient to assure an FTM contamination level below 1 BAB/mL. When silage contains more than 5 log(10) BAB/g, it should not be fed, because it then becomes almost impossible to assure an FTM contamination level below 1 BAB/mL. Measures aimed at improving cattlehouse hygiene, the contamination via soil, and the contamination level of other feeds contribute only marginally to the control of the contamination of FTM with BAB. Application of the modeling methodology could be beneficial for the control of the contamination of FTM with other microorganisms such as Bacillus cereus.
    Analysis of summer epidemic progress of apple scab at different apple production systems in the Netherlands and Hungary
    Holb, I.J. ; Heijne, B. ; Withagen, J.C.M. ; Gáll, J.M. ; Jeger, M.J. - \ 2005
    Phytopathology 95 (2005)9. - ISSN 0031-949X - p. 1001 - 1020.
    venturia-inaequalis - disease-progress - powdery mildew - orchards - conidia - resistance - infection - spores - fungus - buds
    Two, 4-year studies on summer epidemic progress of apple scab were conducted at Randwijk, the Netherlands, from 1998 until 2001 and at Eperjeske, Hungary, from 2000 until 2003. Disease assessments were made on scab-susceptible cv. Jonagold. A range of nonlinear growth functions were fitted to a total of 96 disease progress curves (3 treatment classes x 2 plant parts x 2 disease measures x 4 years x 2 locations) of apple scab incidence and severity. The three-parameter logistic model gave the most consistent fit across three treatment classes in the experiment (integrated, organic-sprayed, and organic-unsprayed). Parameters estimated or calculated from the three-parameter logistic function were used to analyze disease progress. These were disease incidence and severity on the day of the first assessment (Y-s); final disease incidence or upper asymptote for incidence (Y-if) or severity (Y-sf); fruit incidence and severity on day 40, after which no new lesions on fruits appeared (Y-40); leaf incidence and severity on day 75, at which shoot growth stopped (Y-75); relative (beta) and "absolute" (theta) rates of disease progress; inflection point (M); and area under the disease progress curve (AUDPC(5)) standardized by the duration of the total epidemic. Comparisons among disease progress curves were made by Correlation and factor analysis followed by Varimax rotation. There were large differences but high positive correlations among the parameters Y-s, Y-f, theta, and AUDPC(5) across the three treatment classes. In the factor analysis, two factors accounted for more than 85% of the total variance for both incidence and severity. Factor I gave an overall description of epidemic progress of both scab incidence and severity and included the parameters Y-f, Y-40, Y-75, theta, and AUDPCs. Factor 2 identified a relationship between the relative rate parameter (P) and the inflection point (M) for severity and a relationship between disease incidence and severity. For an integrated or an organic orchard, theta, AUDPC(5), and one of Y-f or Y-75 (because of the link with host phenology) can characterize apple scab epidemics during summer. Based on these findings, improved scab management approaches were provided for integrated and organic apple production systems.
    Effect of individual amino acids and glucose on activation and germination of Rhizopus oligosporus sporangiospores in tempe starter
    Thanh, N.V. ; Rombouts, F.M. ; Nout, M.J.R. - \ 2005
    Journal of Applied Microbiology 99 (2005)5. - ISSN 1364-5072 - p. 1204 - 1214.
    mucor-racemosus sporangiospores - germ-tube emergence - conidial germination - stolonifer sporangiospores - nitrogen requirements - neurospora-crassa - spores - viability - proline - carbon
    Aim: To understand the conditions promoting activation and germination of spores, and to contribute to the control of tempe starters. Methods and Results: Using microscopic counts of fluorescent labelled spores, the following results were obtained: (1) L- alanine plays an important role ( of the same order as that of peptone) in stimulation of germination of dormant spores. Alanine can satisfy the requirements of carbon as well as nitrogen for spore germination; (2) L- proline, on the other hand, inhibits alanine uptake presumably by blocking/ congesting transporters of spore cells, resulting in apparent low viability on agar media; (3) L- leucine and L- isoleucine slightly favour spore germination while L- arginine and L- lysine do not have any stimulating effect; (4) The stimulatory role of glucose was only evident in the presence of phosphate ( in minimal medium); when glucose is used in the absence of phosphate, either alone or in combination with single amino acids its role is hardly distinguishable; (5) Phosphate plays a facilitating role in spore germination. Conclusions: Glucose and amino acids play important roles in activation and germination of sporangiospores of Rhizopus oligosporus in tempe starter ( stored for 12 months). The ability and rate of germination of dormant/ old sporangiospores of R. oligosporus, depend on their ability for uptake of individual amino acids and/ or glucose. Significance and Impact of Study: New light was shed on the counteractive role of proline and the stimulating effect of phosphate. Soybeans subjected to traditional preparation for tempe making are heavily leached; germination of starter spores on such beans is sub- optimal, and bean processing could be optimized.
    Meeldauw in komkommer
    Gaag, D.J. van der; Dik, A.J. - \ 2004
    vruchtgroenten - komkommers - komkommerfamilie groenten - sphaerotheca - sporen - rassen (planten) - gewasbescherming - fruit vegetables - cucumbers - cucurbit vegetables - sphaerotheca - spores - varieties - plant protection
    De schimmel tast bladeren en stengels aan. Op de aangetaste delen ziet men wit schimmelpluis. Aantasting kost opbrengst. De veroorzaker van de ziekte is Sphaerotheca fusia. De schimmel kan alleen komkommerachtigen aantasten en groeit op levende plantendelen. De sporen (conidia) kunnen ongeveer een week overleven en kunnen met de wind over grote afstanden worden verspreid. Naast de vatbare rassen zijn er rassen met een redelijk niveau van partiële resistentie en rassen met een hoog niveau van partiële resistentie.
    Dispersal of Venturia inaequalis ascospores and disease gradients from a defined inoculum source
    Holb, I.J. ; Heijne, B. ; Withagen, J.C.M. ; Jeger, M.J. - \ 2004
    Journal of Phytopathology 152 (2004)11-12. - ISSN 0931-1785 - p. 639 - 646.
    combating apple scab - eradicant fungicides - aerial concentration - powdery mildew - wind - epidemics - orchards - release - conidia - spores
    Aerial concentration of ascospores of Venturia inaequalis and incidence of apple scab were monitored in an orchard during the ascospore release seasons in 1999, 2000 and 2001 on susceptible (Jonagold) and moderately resistant (Schone van Boskoop) apple cultivars. A 1-ha orchard was divided into an inoculum source block (approximately 0.34 ha) and an inoculum-free block (approximately 0.66 ha) where inoculum was excluded by covering the soil surface with polythene sheets. Ascospore numbers and disease incidence were measured within the inoculum-free block at different distances from the inoculum block. Ascospores were sampled with three Burkard volumetric spore traps located at 0, 21 and 45 m from the border of the inoculum block. To determine the incidence of infection, clusters of leaves were assessed at six distances from the border of the infected source from the time the first symptoms appeared. Each year, the aerial ascospore concentration significantly decreased with distance from the source, as did the incidence of infected clusters. Cultivar susceptibility to apple scab markedly influenced incidence of infected clusters and disease gradients. The effect of horizontal distance from the source was identifiable up to 18 m and 33 m for cv. Schone van Boskoop and cv. Jonagold, respectively, beyond which disease was negligible. The disease gradients for cultivar Jonagold in 1999, 2000 and 2001 were well described by an exponential model with gradient coefficients of -0.036, -0.042 and -0.047, respectively. The number of infected clusters at the source border for this cultivar differed significantly over the 3 years. A single exponential model with a gradient coefficient of -0.035 adequately described the disease gradients for cultivar Schone van Boskoop in each of the 3 years. Further analysis showed highly significant correlations (r > 0.85, P <0.01) between the annual cumulative spore catches and the annual mean number of infected leaf clusters in each year and for both cultivars. The aerobiological and epidemiological implications of these findings are discussed.
    Behavior of Clostridium perfringens at low temperatures
    Jong, A.E.I. de; Rombouts, F.M. ; Beumer, R.R. - \ 2004
    International Journal of Food Microbiology 97 (2004)1. - ISSN 0168-1605 - p. 71 - 80.
    listeria-monocytogenes - refrigerated foods - fatty-acid - growth - sporulation - beef - spores - vacuum - germination - resistance
    Refrigerated storage is an important step in the preparation of foods and inadequate storage is one of the main causes of food poisoning outbreaks of Clostridium perfringens. Therefore, growth and germination characteristics of C. perfringens in a temperature range of 3-42 degreesC were determined in fluid thioglycollate broth (FTG) and Dutch pea soup. To study the effect of adaptation, cells were either inoculated from a 37 degreesC pre-culture or from a temperature-adapted pre-culture. Membrane fatty acid patterns were determined at all temperatures to examine the effect of temperature on membrane composition. Spores were either inoculated with and without heat treatment. Adaptation of cells did not influence growth rate nor lag phase. Growth in pea soup, however, was slower and lag phases tended to be more extended compared to FTG. No growth was observed at temperatures less than or equal to 10 degreesC and death rates in pea soup were higher than those in FTG at these low temperatures. Cells preserved the membrane fluidity by reducing the arachidic acid content and increasing the lauric acid content when the temperature dropped. This resulted in a net reduction in chain length. Microscopic analysis of cells grown at 15 degreesC revealed a morphological change: cells were elongated compared to those grown at 37 degreesC. These data demonstrate the ability of C. perfringens to adapt to lower temperatures. However, this did not influence growth characteristics compared to non-adapted cells. Spores of C perfringens did germinate at all temperatures with and without heat-activation. Combining this fact with the extended survival at low temperatures emphasizes the need for adequate heating of refrigerated foods before consumption to eliminate health risks due to C perfringens. (C) 2004 Elsevier B.V. All rights reserved.
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