Staff publications - Cranfield Health

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Browsing Staff publications - Cranfield Health by Author "Aldred, David"

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    Environmental factors affect efficacy of some essential oils and resveratrol to control growth and ochratoxin A production by Penicillium verrucosum and Aspergillus westerdijkiae on wheat grain.
    (Elsevier, 2008) Aldred, David; Cairns-Fuller, Victoria; Magan, Naresh
    This study determined the efficacy of three essential oils (bay, clove and cinnamon oil) and the antioxidant resveratrol (0–500 μg g−1) on the control of growth and ochratoxin A (OTA) production by Penicillium verrucosum and Aspergillus westerdijkiae (=A. ochraceus) under different water activity (aw, 0.90, 0.95, 0.995), and temperature (15, 25 °C) conditions on irradiated wheat grain. The most effective treatment (resveratrol) was then tested on natural grain. The ED50 values for growth inhibition by the oils were 200–300 μg g−1 at the aw and the temperatures tested. For resveratrol, this varied from <50 μg g−1 at 0.90–0.95 aw to >350 at 0.995aw at both temperatures. The ED50 values for the control of OTA were slightly lower than for control of growth, with approx. 200 μg g−1 required for the oils and 50–100 μg g−1 of the antioxidant, at 0.90/0.95aw and both temperatures. In wet grain (0.995aw), higher concentrations were required. For growth there were statistically significant effects of single-, two- and three-way interactions between treatments except for concentration×temperature and concentration×temperature×essential oil/antioxidant treatment. For OTA control, statistically significant treatments were aw, temperature×aw, concentration×temperature, treatment×concentration, and three-way interaction of concentration×aw×treatment for P. verrucosum and A. westerdijkiae. Subsequent studies were done with the best treatment (resveratrol, 200 μg g−1) on natural wheat grain with either P. verrucosum or A. westerdijkiae at 0.85–0.995aw and 15/25 °C over 28 days storage. This showed that the populations of the mycotoxigenic species and OTA contamination could be reduced by >60% by this treatment at the end of the storage period.
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    Environmental factors and interactions with mycobiota of grain and grapes: Effects on growth, deoxynivalenol and ochratoxin production by Fusarium culmorum and Aspergillus carbonarius
    (MDPI , 2010-03-18T00:00:00Z) Magan, Naresh; Aldred, David; Hope, Russell; Mitchell, David
    Mycotoxigenic fungi colonizing food matrices are inevitably competing with a wide range of other resident fungi. The outcomes of these interactions are influenced by the prevailing environmental conditions and the competing species. We have evaluated the competitiveness of F. culmorum and A. carbonarius in the grain and grape food chain for their in vitro and in situ dominance in the presence of other fungi, and the effect that such interactions have on colony interactions, growth and deoxynivalenol (DON) and ochratoxin A (OTA) production. The Index of Dominance shows that changes in water activity (aw) and temperature affect the competitiveness of F. culmorum and A. carbonarius against up to nine different fungi. Growth of both mycotoxigenic species was sometimes inhibited by the presence of other competing fungi. For example, A. niger uniseriate and biseriate species decreased growth of A. carbonarius, while Aureobasidium pullulans and Cladosporium species stimulated growth. Similar changes were observed when F. graminearum was interacting with other grain fungi such as Alternaria alternata, Cladopsorium herbarum and Epicoccum nigrum. The impact on DON and OTA production was very different. For F. culmorum, the presence of other species often inhibited DON production over a range of environmental conditions. For A.carbonarius, on a grape-based medium, the presence of certain species resulted in a significant stimulation of OTA production. However, this was influenced by both temperature and aw level. This suggests that the final mycotoxin concentrations observed in food matrices may be due to complex interactions between species and the environmental history of the samples analyzed.
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    Impact of environmental factors on growth and satratoxin G production by strains of Stachybotrys chartarum
    (Wageningen Academic Publishers, 2012-12-31T00:00:00Z) Frazer, Schale; Pestka, James J.; Kim, Jae-Kyung; Medina-Vayá, Ángel; Aldred, David; Magan, Naresh
    The black mould Stachybotrys chartarum and its mycotoxins have been linked to damp building-associated illnesses. The objective of this study was to determine the effects of water availability (water activity, aw) and temperature on growth and production of satratoxin G (SG) by a macrocyclic trichothecene-producing strain (IBT 7711) and non-producing strain (IBT 1495) of S. chartarum. Growth studies were carried out on potato dextrose agar modified with glycerol to 0.995-0.92 aw at 10-37 °C. Growth extension was measured and the cultures were extracted after 10 days and a competitive enzyme-linked immunosorbent assay (ELISA) method used to quantify the SG content. Growth was optimal at 25 to 30 °C at 0.995 aw, but this was modified to 0.98 aw at 30 °C for both strains (1.4- 1.6 mm/day, respectively). The ELISA method revealed that, in contrast to growth, SG production was maximal at 20 °C with highest production at 0.98 aw (approximately 250 μg/g mycelia). When water was freely available (0.995 aw), SG was maximally produced at 15 °C and decreased as temperature was increased. Interestingly, the strain classified as a non-toxigenic produced very low amounts of SG (<1.6 μg/g mycelia) that were maximal at 25 °C and 0.98 aw. Contour maps for growth and SG production were developed from these data sets. These data have shown, for the first time, that growth and SG production profiles are very different in relation to key environmental conditions in the indoor environment. This will be very useful in practically determining the risk from exposure to S. chartarum and its toxins in the built envi
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    The influence of water activity and temperature on germination, growth and sporulation of stachybotrys chartarum strains
    (Springer Science Business Media, 2011-07-01T00:00:00Z) Frazer, Schale; Magan, Naresh; Aldred, David
    The objectives were to determine theinfluence of water activity (aw, 0.997-0.92) andtemperature (10-37C) and their interactions onconidial germination, mycelial growth and sporulationof two strains of Stachybotrys chartarum in vitroon a potato dextrose medium. Studies were carriedout by modifying the medium with glycerol andeither spread plating with conidia to evaluate germinationand germ tube extension or centrally inoculatingtreatment media for measuring mycelialgrowth rates and harvesting whole colonies fordetermining sporulation. Overall, germination ofconidia was significantly influenced by aw andtemperature and was fastest at 0.997-0.98 aw between15 and 30C with complete germination within 24 h.Germ tube extension was found to be most rapid atsimilar aw levels and 25-30C. Mycelial growth ratesof both strains were optimal at 0.997 aw between 25and 30C, with very little growth at 37C. Sporulationwas optimum at 30C at 0.997 aw. However,under drier conditions, this was optimum at 25C.This shows that there are differences in the ranges ofaw x temperature for germination and growth and forsporulation. This may help in understanding the roleof this fungal species in damp buildings and conditionsunder which immune-compromised patientsmay be at risk when exposed to such contaminantsin the indoor air environment.
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    Post-harvest control strategies: Minimizing mycotoxins in the food chain.
    (Elsevier, 2007-10-20) Magan, Naresh; Aldred, David
    Contamination of cereal commodities by moulds and mycotoxins results in dry matter, quality, and nutritional losses and represents a significant hazard to the food chain. Most grain is harvested, dried and then stored on farm or in silos for medium/long term storage. Cereal quality is influenced by a range of interacting abiotic and biotic factors. In the so-called stored grain ecosystem, factors include grain and contaminant mould respiration, insect pests, rodents and the key environmental factors of temperature, water availability and intergranular gas composition, and preservatives which are added to conserve moist grain for animal feed. Thus knowledge of the key critical control points during harvesting, drying and storage stages in the cereal production chain are essential in developing effective prevention strategies post-harvest. Studies show that very small amounts of dry matter loss due to mould activity can be tolerated. With < 0.5% dry matter loss visible moulding, mycotoxin contamination and downgrading of lots can occur. The key mycotoxigenic moulds in partially dried grain are Penicillium verrucosum (ochratoxin) in damp cool climates of Northern Europe, and Aspergillus flavus (aflatoxins), A. ochraceus (ochratoxin) and some Fusarium species (fumonisins, trichothecenes) on temperate and tropical cereals. Studies on the ecology of these species has resulted in modelling of germination, growth and mycotoxin minima and prediction of fungal contamination levels which may lead to mycotoxin contamination above the tolerable legislative limits (e.g. for ochratoxin). The effect of modified atmospheres and fumigation with sulphur dioxide and ammonia have been attempted to try and control mould spoilage in storage. Elevated CO2 of > 75% are required to ensure that growth of mycotoxigenic moulds does not occur in partially dried grain. Sometimes, preservatives based on aliphatic acids have been used to prevent spoilage and mycotoxin contamination of stored commodities, especially feed. These are predominantly fungistats and attempts have been made to use alternatives such as essential oils and anti-oxidants to prevent growth and mycotoxin accumulation in partially dried grain. Interactions between spoilage and mycotoxigenic fungi and insect pests inevitably occurs in stored grain ecosystems and this can further influence contamination with mycotoxins. Effective post-harvest management of stored commodities requires clear monitoring criteria and effective implementation in relation to abiotic and biotic factors, hygiene and monitoring to ensure that mycotoxin contamination is minimised and that stored grain can proceed through the food chain for processing.
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    Water activity, solute and temperature modify growth and spore production of wild type and genetically engineered Aspergillus niger strains.
    (Elsevier, 2004-08-05) Parra, Roberto; Aldred, David; Archer, David B.; Magan, Naresh
    The effect of interactions of water activity (aw) (0.99–0.90), temperature (20, 30 and 35 °C) and modifying aw solute (glycerol, NaCl) on growth and sporulation of a wild-type strain of Aspergillus niger (W) and two genetically engineered lysozyme-producing strains (L11, B1) was examined for the first time. Maximum growth rates were achieved for both strains (L11 and B1) under moderate aW levels. L11 showed a higher growth rate than B1. Fastest growth was achieved at 30 °C, using glycerol as solute. Optimum conditions for growth of strain L11 were estimated by means of contour plot surfaces and found to be 0.965 aw with glycerol as solute at 35 °C. The predicted value of the optimum growth rate was 10.5 mm/day. A value of 10.85 mm/day was obtained experimentally giving a good correlation between the estimated and the measured results. Sporulation was optimum for the W strain at 0.99–0.95 by B1 at 35 °C. Significant higher production of conidia by L11 at 0.97–0.93 aw and at 0.97 aw and 35 °C for B1 strain was observed. Optimum conditions for spore production were different from those for growth. Under similar ecological conditions, the W and both the genetically engineered strains had a different growth and sporulation pattern.