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  • 1
    ISSN: 1573-0832
    Keywords: Aflatoxin ; broad bean ; cultivars ; fungi ; hybrid ; mycotoxins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract One hundred different cultivars and lines of broad bean (Vicia faba L.) seed samples were inoculated with Aspergillus flavus Link (CMI 102135) to determine varietal differences which may support or resist aflatoxin production. Thin-layer chromatographic analysis of the chloroform extracts of the different seed samples revealed that 11 cultivars/lines were highly resistant to seed invasion and aflatoxin production while 9 cultivars/lines showed partial resistance. The remaining 80 samples were susceptible to the establishment of A. flavus and aflatoxin accumulation. All the resistant cultivars/lines seed samples were inoculated also with three local isolates of fungi namely; Stachybotrys chartarum (Ehrenb. ex Link) Hughes, Aspergillus ochraceus Wilhelm, and Fusarium oxysporum Schlecht. The resistant seed samples were also resistant for colonization with these fungi and mycotoxin formation.
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  • 2
    ISSN: 1573-0832
    Keywords: Aflatoxin ; Breast milk ; Ochratoxin A ; Sierra Leone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Breast milks from 113 mothers in two ‘Under-Five Clinics’ in the Southern Province of Sierra Leone, namely, Njala and Bo, were examined for their mycotoxin content. Only 10 were mycotoxin-free. Eighty-eight per cent of samples contained various aflatoxins and 35% contained ochratoxin A (OTA). Few samples (15%) had a single mycotoxin. Thirty-six (32%) had two mycotoxins and 50 (40%) had three or more. The occurrence of OTA in combination with various aflatoxins was recorded. It is concluded that infants in Sierra Leone are exposed to OTA and aflatoxins at levels which in some cases far exceed those permissible in animal feed in developed countries.
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  • 3
    ISSN: 1573-0832
    Keywords: Brain ; Aflatoxin ; Children ; Nigeria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Autopsy brain (cerebrum) specimens from 18 kwashiorkor children and 19 children who had died from a variety of other diseases, at the Obafemi Awolowo Teaching Hospital complex, Ile-Ife, Nigeria, were analysed for the presence of aflatoxins using high-performance liquid chromatography. Aflatoxins were detected in 81%, 15 specimens in each group. More than one type of aflatoxin was detected in 14 (37.8%) of all the specimens. Aflatoxin B1 and its reversible metabolite, aflatoxicol, were detected in 11 brain specimens of patients with kwashiorkor and 6 of those who died of other miscellaneous diseases; out of these 6, two died from measles and its complications. The frequent detection of aflatoxins in the brains of these children and sometimes in multiple forms may suggest that aflatoxins are stored in the brain tissue which could be related to the lipophilic nature of these compounds. These findings also suggest that although many children in the tropics are exposed to aflatoxins, the accumulation of aflatoxin B1 and aflatoxicol in the brains of kwashiorkor children may be a result of an impaired metabolism of these compounds by these children.
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  • 4
    ISSN: 1573-0832
    Keywords: Aflatoxin ; soya-bean root ; leucine ; mycotoxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The present work reports a portion of our continuing effort to determine the mechanism(s) whereby aflatoxins cause toxic responses in in vitro cultured plant tissues. Few investigations have dealt with the mode of action of aflatoxin B1 (AFB1) in excised plant tissues. Here is detailed AFB1 influence on growth, uptake and incorporation of 14C-leucine by excised, incubated soya-bean roots. Pure AFB1 was added to culture medium prior to autoclaving. One gram fresh weight portions of roots from three-day old soya-bean seedlings were excised and incubated for 4, 8, 12 and 24 hours. Growth was assayed by following changes in root dry weight. Aflatoxin B1 inhibited root dry weight at both 20 and 30 μg/ml. Uptake of 14C-leucine was checked by following its depletion from the medium. Reduced 14C-leucine uptake by roots exposed to 20 μg/ml AFB1 suggests that the toxin may alter the plasmalemma. A possible role for AFB1 in modification of membrane-associated amino acid transport mechanisms is discussed. Incorporation of 14C-leucine into trichloroacetic acid-precipitable cytoplasm was assayed. Inhibition of this incorporation at 20 μg/ml AFB1 was most apparent at 12 hours. Thus, AFB1 may also impair the ability of excised soya-bean roots to carry out protein synthesis.
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  • 5
    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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  • 6
    ISSN: 1573-0832
    Keywords: Aflatoxin ; Aspergillus flavus ; Central Japan ; Soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In Kanagawa Prefecture, located in central Japan, aflatoxin-producingAspergillus flavus was isolated in 4 (2.5%) of 160 field soil samples. In the 4 fields, whose soil contained aflatoxin-producingA. flavus, the annual average temperature of the sampling sites of the soil ranged from 13.8 to 15.1°C. Of all the isolated strains of aflatoxin-producingA. flavus, 4 strains, isolated from a single soil sample, produced large amounts of aflatoxin B1 and B2 when incubated in coconut agar, peanut agar, peanuts or trilaurin-added rice, although they did not produce aflatoxin when incubated in rice, yeast extract-sucrose broth or sucrose-low salts broth.
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  • 7
    ISSN: 1573-0832
    Keywords: Aflatoxin ; Biodeterioration ; ‘Donkwa’ ; Fungi ; Relative humnidity ; Storage time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A total of 14 fungal species, mostly toxigenic, were isolated from 50 samples of ‘donkwa’ snack obtained from 16 producers. All of the isolates recorded substantial growth, though at varying rates, on the 2% snack agar provided. They also induced a reduction in the oil and an increase in free fatty acids of the substrate suggesting their participatory roles in deterioration. Most of the snack samples analysed contained initial amounts of aflatoxins above the ‘safe’ permissible level (30 ppb). The initial toxin levels increased substantially with storage time under 79.5, 89.5 and 100% ambient relative humidities but increased only slightly when samples were kept at 71% relative humidity. Almost constant toxin levels were recorded throughout the study period under 51% relative humidity. Accumulation of aflatoxin B1 in samples was most enhanced at 89.5% relative humidity. Comparatively, greater amounts of aflatoxin B1 accumulated under all conditions than the amounts recorded for aflatoxin G1.
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  • 8
    ISSN: 1573-0832
    Keywords: Aflatoxin ; Aspergillus ; Versicolorin B ; Versiconal hemiacetal acetate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The sequence of steps versiconal hemiacetal acetate (VHA) to versiconal (VL) catalyzed by an esterase and VL to versicolorin B (VB) catalyzed by VL cyclase has been previously demonstrated in cell-free systems fromAspergillus parasiticus. VHA esterase and VL cyclase activities were estimated by determining the amounts of VL and VB after incubation of VHA in cell-free extracts from mycelia that were either synthesizing or not synthesizing aflatoxins. VHA esterase activity but not VL cyclase activity was present in extracts from cells grown in a nonaflatoxin-producing medium. VHA esterase activity was present in extracts from mycelia grown in aflatoxin-producing medium harvested after one to six days of incubation. VL cyclase activity was absent at one day, low at two days, maximal at three to five days, and lower at six days. VL cyclase activity appears in the later part of the growth period which is also the period of aflatoxin biosynthesis. This supports a role for VL cyclase in the aflatoxin biosynthetic pathway.
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  • 9
    ISSN: 1573-0832
    Keywords: Aflatoxin ; Aspergillus flavus ; Fumonisins ; Fusarium ; Maize ; Mycotoxins ; Stenocarpella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Sixty nine samples of maize were collected from pre-harvest standing crops and on-farm storage facilities from 52 smallholder farms located within 4 regions of Honduras during October 1992 and November 1993. Samples were visually assessed for insect damage and fungal spoilage, and the mycoflora quantified on artificial media. The major components of the ear rot complex were:Fusarium moniliforme, F. moniliforme var.subglutinans, Penicillium species,Stenocarpella maydis, S. macrospora andAcremonium spp. Representative samples were also assayed for mycotoxin content. Fumonisin B1 was detected in all 24 samples tested at levels of between 68–6,555 (µg/kg), and aflatoxin was detected in 2 samples heavily contaminated withAspergillus flavus. Moniliformin and tenuazonic acid were not detected in the samples tested. The implications of these findings for human and livestock health risk are discussed, together with possible strategies for controlling these pathogens.
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  • 10
    ISSN: 1573-0832
    Keywords: Aflatoxin ; aflR ; Aspergillus parasiticus ; repressor ; sclerotia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Regulation of aflatoxin (AF) biosynthesis likely involves a complex interplay of positive- and negative-acting factors that are affected by physiological cues responsive to internal and external stimuli. These factors, presumably, modulate the expression of the AF pathway-specific regulatory gene, aflR, whose product, AFLR, a zinc cluster transcription factor, then turns on or off the transcription of other AF genes. To determine if the AFLR carboxyl region (AFLRC) interacts with positive-or negative-acting proteins, we fused the Aspergillus parasiticus aflR carboxyl coding region(aflRC) to the promoter of A. parasiticusnitrite reductase gene (niiA(p)::aflRC), and transformed it into A. parasiticus SRRC 2043. Transformants that contained two copies of niiA(p)::aflRC, one at the niaD locus and another at the aflR locus, over produced AF precursors independent of the nitrogen source. The higher copy number of the integrated niiA(p)::aflRC correlated with increased production of AF precursors by the transformants as well as increased expression of both aflRC and native aflR in potato dextrose broth and A & M medium. Since aflRC does not encode a DNA-binding domain, the expressed AFLRC should not bind to the promoters of AF pathway genes and affect transcription directly. The results are consistent with AFLRC titrating out a putative repressor that interacts with AFLR under different growth conditions and modulates AF biosynthesis. This interaction also indirectly affects sclerotial development.
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