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PubMed2001

New additive for culture media for rapid identification of aflatoxin-producing Aspergillus strains.

A new reliable, fast, and simple method for the detection of aflatoxigenic Aspergillus strains, consisting of the addition of a cyclodextrin (a methylated beta-cyclodextrin derivative) to common media used for testing mycotoxin production ability, was developed. We propose the use of this compound as an additive for fungal culture media to enhance the natural fluorescence of aflatoxins. The production of aflatoxins coincided with the presence of a bright blue or blue-green fluorescent area surrounding colonies when observed under long-wavelength (365-nm) UV light after 3 days of incubation at 28 degrees C. The presence of aflatoxins was confirmed by extracting the medium with chloroform and examining the extracts by high-pressure liquid chromatography with fluorescence detection.

Aflatoxins↗

PubMed2006

Molecular analysis of an inactive aflatoxin biosynthesis gene cluster in Aspergillus oryzae RIB strains.

To help assess the potential for aflatoxin production by Aspergillus oryzae, the structure of an aflatoxin biosynthesis gene homolog cluster in A. oryzae RIB 40 was analyzed. Although most genes in the corresponding cluster exhibited from 97 to 99% similarity to those of Aspergillus flavus, three genes shared 93% similarity or less. A 257-bp deletion in the aflT region, a frameshift mutation in norA, and a base pair substitution in verA were found in A. oryzae RIB 40. In the aflR promoter, two substitutions were found in one of the three putative AreA binding sites and in the FacB binding site. PCR primers were designed to amplify homologs of aflT, nor-1, aflR, norA, avnA, verB, and vbs and were used to detect these genes in 210 A. oryzae strains. Based on the PCR results, the A. oryzae RIB strains were classified into three groups, although most of them fell into two of the groups. Group 1, in which amplification of all seven genes was confirmed, contained 122 RIB strains (58.1% of examined strains), including RIB 40. Seventy-seven strains (36.7%) belonged to group 2, characterized by having only vbs, verB, and avnA in half of the cluster. Although slight expression of aflR was detected by reverse transcription-PCR in some group 1 strains, including RIB 40, other genes (avnA, vbs, verB, and omtA) related to aflatoxin production were not detected. aflR was not detected in group 2 strains by Southern analysis.

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PubMed1966

Survey of the sensitivity of microorganisms to aflatoxin.

Among the 329 microorganisms tested for aflatoxin sensitivity were 30 genera of bacteria, 34 genera of fungi, 4 genera of algae, and 1 protozoan. Twelve species of the genus Bacillus, a clostridium, and a streptomycete were inhibited when 30 mug/ml of crude aflatoxin (36% pure) was incorporated into the growth substrate. A strain of Bacillus brevis and two of B. megaterium were most sensitive to aflatoxin, being inhibited at 10 and 15 mug/ml, respectively.

Aflatoxins↗

PubMed1968

Investigation of reported aflatoxin production by fungi outside the Aspergillus flavus group.

A screening study of 121 fungus isolates, representing 29 species, for aflatoxin synthesis demonstrated this property only in Aspergillus flavus and A. parasiticus. Eight of the organisms found negative were isolates reported by other investigators to produce aflatoxin. Since similar negative reports have come from several other workers, it is concluded that only the A. flavus group of Aspergillus can presently be certified as sources of these toxins. Reasons for possible false-positive findings are discussed along with precautionary measures and differential analytical procedures useful in aflatoxin screening studies.

Aflatoxins↗

PubMed1968

Effect of diurnal temperature cycles on the production of aflatoxin.

Exposures to short periods of high temperature (40 to 50 C) in each 24-hr diurnal temperature cycle (average temperature ca. 25 C) reduced growth of Aspergillus parasiticus and production and accumulation of the aflatoxins when compared with cultures held continuously at 25 C. In contrast, diurnal cycles with an average temperature of ca. 25 C but with minima as low as 10 C did not appreciably affect either growth or toxin production. The ratio of production of aflatoxin B to aflatoxin G increased as the maximal temperature was raised but remained essentially unchanged with decreasing minimal temperatures.

Aflatoxins↗

PubMed1970

Aflatoxin B1 induction of lysogenic bacteria.

A technique for biological verification of aflatoxin B(1) was developed based on toxin-mediated induction of lysis in a lysogenic strain of Bacillus megaterium NNRL B-3695. Reduction of culture turbidity was determined at various concentrations of toxin. Incubation of 1.1 x 10(-4) g (dry weight) of cells/ml of growth medium containing 25 mug of B(1) per ml at 37 C reduced initial turbidity 0.20 absorbance units in 4 hr. If the bacterial lysate of the lysogenic strain, after a 2-hr incubation with 25 mug of B(1) per ml, was plated with a sensitive B. megaterium strain (NRRL B-3694), plaque-forming units increased approximately 150 times relative to the control. Comparable testing of the effects of aflatoxin on the nonlysogenic, sensitive strain demonstrated that 75 mug of B(1) per ml neither induced lysis nor plaque-forming units. Although induction is not an exclusive property of aflatoxin B(1), the differential response of the lysogenic and sensitive Bacillus strains to B(1) offers a unique and rapid technique for biological verification of the toxin.

Aflatoxins↗

PubMed1971

High aflatoxin production on a chemically defined medium.

Aspergillus parasiticus ATCC 15517 produced 28 to 30 mg of aflatoxin per 100 ml of a medium containing sucrose, asparagine, and salts in stationary and shaken cultures. In the absence of asparagine in the medium, the toxin yields fell drastically, and the thin-layer chromatograms of the chloroform extracts of the cultures indicated the total absence of aflatoxin G(1) and the presence of new intense blue and green fluorescent bands having R(F) values lower than aflatoxins. Initial pH was critical and had to be around 4.5 for good growth and high toxin production on this medium. Optimum concentrations of KH(2)PO(4) and MgSO(4).7H(2)O in the medium were much lower than those normally used in fungal growth media.

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PubMed1973

Improved yield of aflatoxin by incremental increases of temperature.

Increasing the initial temperature of the rice fermentation of Aspergillus parasiticus NRRL 2999 from 15 to 21 C after 24 h of incubation and then to 28 C after 48 h resulted in about a fourfold increase in total aflatoxin over the usual fermentation which is held constant at 28 C for 6 days. The percentage of aflatoxin B(1), the most toxic component, in the total aflatoxin was also increased.

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PubMed1974

Aflatoxin-producing strains of Aspergillus flavus detected by fluorescence of agar medium under ultraviolet light.

The fluorescence method of detecting aflatoxin-producing strains of Aspergillus flavus and related species utilizes the ultraviolet-induced fluorescence of aflatoxin produced in a modified Czapek's solution agar containing corn steep liquor, HgCl(2), and (NH(4))H(2)PO(4) instead of NaNO(3). The presence of aflatoxin is confirmed by thin-layer chromatography of CHCl(3) extracts of the fluorescing agar.

Aflatoxins↗

PubMed1974

Aspergillus flavus infection and aflatoxin production in corn: influence of trace elements.

Distribution of trace element levels in corn germ fractions from kernels naturally infected with Aspergillus flavus and from kernels free of the fungus demonstrated an association between the presence of A. flavus and higher levels of metals. A. flavus production of aflatoxin on various autoclaved corn media showed that ground, whole corn was an excellent substrate; similar high levels of toxin were observed on full-fat corn germ but endosperm and defatted corn germ supported reduced yields. The influence of trace elements and their availability in defatted corn germ to A. flavus-mediated aflatoxin biosynthesis were measured. Enrichment of the substrate with 5 to 10 mug of manganese, copper, cadmium, or chromium per g of germ increased toxin yields. Addition of lead or zinc (50 to 250 mug/g) also enhanced toxin accumulation. Aflatoxin elaboration was reduced by the addition of 25 mug of cadmium per g or 500 mug of copper per g of germ.

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PubMed1974

Further characterization of tissue distribution and metabolism of (14C)aflatoxin B1 in chickens.

The distribution and metabolism of [(14)C]aflatoxin B(1) in chicken tissues were further investigated. Previously dried and frozen ethyl acetate extracts of liver, heart, gizzard, breast, leg, blood, and fecal samples were obtained from either layer or broiler chickens fed subclinical levels of [(14)C]aflatoxin B(1). Treatment of these extracts with either carboxypeptidase A, leucine aminopeptidase, pepsin, or trypsin revealed that an average of 50% of the (14)C detected in the acetate extracts was a liberated peptide (or amino acid) conjugate of [(14)C]aflatoxin B(2a). When a prepared standard of B(2a) was made by incubation of B(1) with cold dilute aqueous HCl, the R(f) values and absorbance maxima were identical with those of the tissue extracts after enzymatic treatment.

Acetates↗

PubMed1975

Effect of ochratoxin and aflatoxin on serum proteins, complement activity, and antibody production to Brucella abortus in guinea pigs.

The effect of ochratoxin alone and in combination with aflatoxin and Brucella abortus antigen on complement activity, serum proteins, and antibody response in guinea pigs was investigated. Ochratoxin did not affect complement activity or antibody response and there was no interaction between ochratoxin and aflatoxin on any of the responses tested. Ochratoxin significantly lowered the level of beta-globulin in serum of guinea pigs. There was no significant interaction between aflatoxin and antigen on lowering of the serum albumin levels of guinea pigs.

Aflatoxins↗

PubMed1975

Influence of modified atmosphere storage on aflatoxin production in high moisture corn.

Samples of freshly harvested corn and remoistened corn were inoculated with Asphergillus flavus and stored for 4 weeks at about 27 C in air and three modified atmospheres. Aflatoxins and fat acidity were determined weekly. Corn stored in the modified atmospheres did not accumulate over 15 mug of total aflatoxins per kg. Corn from the high CO2 treatment (61.7 per cent CO2, 8.7 per cent O2, and 29.6 per cent N2) was visibly molded at 4 weeks and had a higher fat acidity than the other treatments. In the N2 (99.7 per cent N2 and 0.3 per cent O2) and controlled atmosphere (13.5 per cent CO2, 0.5 per cent O2, 84.5 per cent N2) treatments, a fermentation-like odor was detected. When the corn was removed from the modified atmospheres it deteriorated rapidly and was soon contaminated with aflatoxins.

Aflatoxins↗

PubMed1975

Effect of initial pH on aflatoxin production.

The effect of initial pH on aflatoxin production by Aspergillus parasiticus NRRL 2999 was examined in a semisynthetic medium. Maximal growth, aflatoxin production, and aflatoxin production per unit of growth occurred at initial pH levels of 5.0, 6.0, and 7.0 respectively. Initial pH levels less than pH 6.0 favored production of the B toxins, whereas levels greater than pH 6.0 favored production of the G toxins.

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PubMed1987

Determination of glucose level needed to induce aflatoxin production in Aspergillus parasiticus.

Previous studies have established that aflatoxin production is induced by high levels of glucose (or other compatible carbohydrates). However, the minimal amount of glucose needed to achieve this effect had not been determined. Aspergillus parasiticus was induced to produce aflatoxin when incubated for 18 h in the presence of greater than or equal to 0.1 M glucose before addition of cycloheximide. Toxin formation was not induced at any glucose concentration in the mycelia incubated for 8 h. These results suggest that aflatoxin synthesis would not be expected in substrate containing less than 0.1 M of a carbohydrate source.

Aflatoxins↗

PubMedDate not supplied

A study on the isolation of aflatoxin-producing strains from agricultural products in Korea.

In order to isolate aflatoxin-producing strains from agricultural products in the Youngnam district of Korea, rice, barley, unhulled barley, corn, soybean, Meju (soybean paste), peanut, and soil samples were collected from markets or homes. From the 347 samples, 280 strains of Aspergillus spp. were isolated. As a result of screening by thin layer chromatography (TLC), 29 strains showed fluorescent spot and four strains had the same Rf values as those of standard aflatoxins. The percentage of contamination of aflatoxin-producing strains was 1.4%. The four strains were classified as the Aspergillus flavus group by the examination of characteristics and morphology.

Aflatoxins↗

PubMed1995

Fusarium mycotoxins (fumonisins, nivalenol, and zearalenone) and aflatoxins in corn from Southeast Asia.

Corn samples collected from the Philippines, Thailand, and Indonesia were surveyed for the natural occurrence of Fusarium mycotoxins (fumonisins, trichothecenes, and zearalenone) and aflatoxins. Fumonisins B1 and B2 were found in over 50% of corn samples in individual countries, and their co-occurrences with aflatoxins at the incidence of 48% were noted. In addition to these mycotoxins, a trichothecene, nivalenol, and an estrogen, zearalenone, both mycotoxins of Fusarium species, were detected in these Southeast Asian samples. This is the first report on the simultaneous occurrence of two carcinogenic mycotoxins, fumonisins and aflatoxins, together with Fusarium mycotoxins (nivalenol and zearlenone) in corn from Asian tropics.

Aflatoxins↗

PubMed1995

Toward less misleading comparisons of uncertain risks: the example of aflatoxin and alar.

Critics of comparative risk assessment (CRA), the increasingly common practice of juxtaposing disparate risks for the purpose of declaring which one is the "larger" or the "more important," have long focused their concern on the difficulties in accommodating the qualitative differences among risks. To be sure, people may disagree vehemently about whether "larger" necessarily implies "more serious," but the attention to this aspect of CRA presupposes that science can in fact discern which of two risks has the larger statistical magnitude. This assumption, encouraged by the indiscriminate calculation of risk ratios using arbitrary point estimates, is often incorrect: the fact that environmental and health risks differ in unknown quantitative respects is at least as important a caution to CRA as the fact that risks differ in known qualitative ways. To show how misleading CRA can be when uncertainty is ignored, this article revisits the claim that aflatoxin contamination of peanut butter was "18 times worse" than Alar contamination of apple juice. Using Monte Carlo simulation, the number 18 is shown to lie within a distribution of plausible risk ratios that ranges from nearly 400:1 in favor of aflatoxin to nearly 40:1 in the opposite direction. The analysis also shows that the "best estimates" of the relative risk of aflatoxin to Alar are much closer to 1:1 than to 18:1. The implications of these findings for risk communication and individual and societal decision-making are discussed, with an eye toward improving the general practice of CRA while acknowledging that its outputs are uncertain, rather than abandoning it for the wrong reasons.

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