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  • 1
    ISSN: 1573-0832
    Keywords: aflatoxin ; Aspergillus flavus ; non-toxigenic O-methylsterigmetocystin ; sterigmetocystin ; nontoxigenic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Non-aflatoxin-producing isolates ofAspergillus flavus from nature and isolates ofA. flavus that had lost their toxigenic trait following laboratory transfer were compared biochemically. After the addition of aflatoxin B1 precursors sterigmatocystin or O-methylsterigmatocystin to whole cell cultures, the non-toxin producing isolates from nature remained non-toxigenic while toxigenicity was restored in the nontoxigenic laboratory strains. Results imply a lack of enzymes needed for biochemical conversions of precursors to aflatoxin B1 in natural non-producers and suppression of these enzymes in the nonproducing laboratory strains.
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  • 2
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; aflatoxin ; cytochemistry ; Gossypium ; ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Cottonseeds having fluorescent fibers were harvested from fields in Arizona and examined utilizing light microscopy and transmission electron microscopy. The occurrence of fluorescent fibers indicated that seeds had been infected by Aspergillus flavus during development. Presence of A. flavus was verified by plating portions of seeds with fluorescent fibers. Hyphae, conidial heads, and conidia were identified readily in differentially-stained cotyledon tissue processed for light microscopy. Utilization of transmission electron microscopy permitted observations on lignified seed coats and cotyledons of mature cottonseeds. Hyphae were located throughout the cotyledon and in the nonlignified layers of the seed coat. The identification of hyphae in cross sections of vessel elements within the seed coat provided ultrastructural evidence supporting the hypothesis that A. flavus may enter seeds via the vascular tissue. Controls for the microscopy studies included observations on cottonseeds with no visual signs of infection and on laboratory-grown cultures of A. flavus. These observations demonstrated that the hyphae localized within fluorescent seeds had features characteristic of A. flavus and that fungal-like structures do not occur within uninfected seeds.
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  • 3
    ISSN: 1573-0832
    Keywords: Storage fungi ; mycotoxins ; food contaminants ; Aspergillus flavus ; Aspergillus Candidas ; aflatoxin ; rice bran ; raw rice ; parboiled rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Thirty four samples of rice bran, of which 9 were from raw (untreated) rice (RR) and 25 from parboiled rice (PbR) were collected from commercial rice mills in and around Madras and analysed for storage mycoflora and mycotoxins. Fungi of the Aspergillus flavus group were present in 29 of the 34 samples (8 from RR and 21 from PbR) in quantities ranging from 〈1–432 thousand propagules/g, though not always as the dominant mycoflora. Fungal numbers were usually higher in RR than in PbR samples. Five of the 9 RR samples and 6 of the 25 PbR samples were positive for aflatoxins. Among 29 isolates of A. flavus obtained from the bran samples, 16 isolates −6 from RR bran and 10 from PbR bran — were found to be toxigenic in vitro. Some isolates of A. candidus also seemed to produce aflatoxin and other fluorescent substances.
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  • 4
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; Sri Lanka
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The fungal flora of 6 Asian medicinal plants, Aerva lanata (Linn.) Juss. Alyssicarpus vaginalis D.C., Tribulus terrestris Linn. Adhatoda vasica Nees., Centella asciatica (L.) Urb., Cardiospermum halicacabum Linn. was determined. After surface disinfection Aspergillus spp. were most frequently observed. Aspergillus flavus, isolated from Alyssicarpus vaginalis and Aerva lanata produced aflatoxins in culture. Aflatoxin B1 was also detected in a sample of Aerra lanata at a level of 0.5 μg/g. Plant material destined for medicinal use should be stored carefully prior to its use to prevent growth of naturally occurring toxigenic mold fungi.
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  • 5
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; Aflatoxins ; Culture method ; Glass fiber
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A new method for growingAspergllius flavus for experimental studies is presented. The system consists of a humidified vial with a thick septum pierced by a pin on which a glass fiber disc is affixed. The disc contains the test solution and inoculum plus medium. The method has been used to assess the effect of variations in culture conditions on production of aflatoxin B1 (AFB1). The AFB1 level was affected by the amount of medium placed on the disc and type of disc material. The results for different types of glass fiber and quartz discs were compared with AFB1 produced by fungus grown in liquid medium or on paper discs. When compared to a liquid medium culture there was a 15 to 20-fold increase in AFB1 for one type of disc. Incubations with less than 14 µl of medium gave satisfactory results. A crude phosphatidylcholine preparation at a concentration of 0.7% of the medium resulted in a 4-fold increase in AFB1.
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  • 6
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; Elastase ; Elastinolytic ; Metalloproteinase ; Serine proteinase ; Toxigenic fungus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A survey of the distribution of elastinolytic potential among 32 culture collection isolates ofAspergillus flavus, A. oryzae, A. parasiticus, A. sojae, A. nomius, andA. tamarii revealed this character to be highly conserved withinAspergillus SectionFlavi. Furthermore, 144 isolates ofA. flavus from environmental samples from six separate regions of the United States produced elastase on solid medium. Most previously described polymorphisms in elastinolytic potential were attributed to the toxicity of borate buffers. Replacement of borate with HEPES (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) resulted in detection of elastase production on solid medium by all tested fungal isolates except two that had been in culture over 50 years. In liquid culture, only isolates ofA. flavus, A. tamarii, andA. oryzae accumulated elastase activity. Although isoelectric focusing revealed only one isoform (pI 9.0) of elastase in these culture filtrates, elastinolytic activity in filtrates was partially inhibited by both 1,10-phenanthrolene (2 mM) and phenylmethylsulfonylfluoride (2 mM), suggesting the presence of both metallo and serine elastinolytic proteinases.
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  • 7
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; aflatoxin ; fungal competition ; barley grain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Colonization of barley grain by Aspergillus flavus and formation of aflatoxin B1 in the presence of Penicillium verrucosum, Fusarium sporotrichioides, and Hyphopichia burtonii were studied over a three-week period in all combinations of 20 or 30 °C and 0.97, 0.95 or 0.90 aw. Grain colonization was assessed initially by observing hyphal extension on the grain surface, using scanning electron microscopy, and then from the proportion of seeds infected and numbers of colony forming units (cfu) formed. Aflatoxin b1 concentrations were determined by enzyme linked immunosorbent assay using a monoclonal antibody. These studies showed that interaction between A. flavus and other fungi in paired culture had different effects on both colonization and aflatoxin formation depending on the species involved and environmental conditions. Germination of A. flavus spores was unaffected by the presence of other species on the grain surface. Subsequently, three principal patterns of A. flavus colonization of barley grain were observed through the incubation period in the presence of other fungal species: (a) colonization unaffected by the presence of other species; (b) colonization initially slower in the presence of other species but later differing little from pure cultures; and (c) colonization adversely affected by the presence of other species. Five main patterns of aflatoxin B1 production were observed relative to pure culture but with no consistent relationship with species, aw, temperature or incubation period; (a) little changed; (b) increased slowly; (c) decreased; (d) enhanced; and (e, f) increased initially but later decreased to (e) the same level as in pure culture or (f) to less than in pure culture. Generally, production of aflatoxin B1 by A. flavus was less than in pure culture but sometimes was changed only slightly by the presence of P. verrucosum, F. sporotrichioides or H. burtonii or was temporarily enhanced.
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  • 8
    ISSN: 1573-0832
    Keywords: Aspergillus flavus ; starch ; reducing sugars ; kojic acid ; aflatoxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Depletion of sugar and starch carbon sources and concomitant formation of secondary fungal metabolites, aflatoxin and kojic acid, were examined in growing corn inoculated with Aspergillus flavus. Kernels from control and inoculated ears were removed and analyzed after 16, 24, 48, 96 and 168 hrs. Reducing sugars were not significantly different for inoculated and control non-inoculated samples, but after 168 hrs (seven days) starch content was 20% lower in inoculated than in control samples. Kojic acid was detected before aflatoxins formed. Kojic acid, the oxidized product of kojic acid, and aflatoxin were all present in samples two days from inoculation. The formation of this oxidation product may influence toxin levels.
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  • 9
    ISSN: 1573-0832
    Keywords: mixed poultry feeds ; fungi ; Aspergillus flavus ; aflatoxins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A survey was carried out in Reunion island to obtain data on the occurrence of fungi, aflatoxigenic strains of Aspergillus flavus, aflatoxins, total aerobic bacteria and salmonellae of 150 samples of mixed poultry feeds and raw materials. These were collected at five farms over a 3-month period during the warm rainy season. White corn and Brazilian soybean meal seemed to present a better microbiological quality than yellow corn and US soybean meal. Mixed poultry feeds presented a high total mold count reflecting the mold flora of raw materials. The most frequent and abundant fungi were Aspergillus flavus, A. glaucus group, Fusarium spp., Penicillium spp., A. candidus, Mucor spp., A. restrictus, Scopulariopsis spp., Cladosporium spp. and A. versicolor. Of the 118 A. flavus strains screened, 42 (35.6%) were aflatoxigenic. Yellow corn samples were the most frequently contamined with aflatoxigenic strains (54.5%), followed by mixed feeds (44%). Of the 66 samples tested, 24 (36%) contained aflatoxins (traces to 22 ng/g). A good correlation seemed to exist between presence of at least one aflatoxigenic strain per sample and presence of aflatoxins.
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  • 10
    ISSN: 1573-0832
    Keywords: Aflatoxin ; Aspergillus flavus ; aflatoxin natural ; semisynthetic and synthetic media
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We have studied the aflatoxin producing capacity of 41 Aspergillus flavus strains isolated from the mycoflora present of natural media (wheat, rice and mixed feed) synthetic medium (Aflatoxin Producing Ability Medium) and semisynthetic media (Coconut Agar Medium and Glucose Yeast Extract Agar) were compared. Aflatoxins were analysed on days 4 and 8 post-inoculation under an incubation temperature of 28 °C. A total of 30 strains (75.7%) were producers on natural media as detected by Thin Layer Chromatography: 23 strains on wheat, 27 on rice and 12 on mixed feed. The results by qualitative flourescence tests on synthetic and semisynthetic media were: 3 strains positive on Coconut Agar Medium (CAM) 1 on Glucose Yeast Extract Agar (GY + Agar) and none on Aflatoxin Producing Ability Medium (APA).
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