Effect of Dietary Aflatoxin Concentration on the Assessment of Genetic Variability of Response in a Randombred Population of Chickens

The effect of graded levels of dietary aflatoxin on the assessment of genetic variability of body weight and gain and plasma protein response was tested utilizing the Athens-Canadian randombred population of chickens. Dietary aflatoxin was administered at levels of either 0, 1.25, 2.50 or 5.0 µg/g of diet ad libitum from 7 to 21 days of age to progeny from 58 sire families. Twenty-one-day body weights, gain and plasma protein concentration were used to assess the variation in response.—The administration of increasing levels of aflatoxin resulted in a dose-related decrease of gains and plasma protein concentrations. Plasma protein concentrations were significantly higher among males than females within the control group; however, this difference was reversed as the severity of the aflatoxin challenge increased. Heritability estimates for all responses increased as the level of aflatoxin administered increased. This change was most notable for total plasma protein concentration. Phenotypic correlations for plasma protein concentration and growth measurements tended to diminish with increasing levels of aflatoxin. A similar trend was noted for the genetic correlations; however, a moderate correlation between growth responses and plasma protein response was detected in the 5.0-µg/g aflatoxin treatment group. Genetic correlations were calculated for the same characters between the different levels of aflatoxin. Regardless of which aflatoxin challenges were compared, a very high genetic correlation for 21-day body weight and 7- to 21-day gain was estimated. This variation in growth potential in the toxic environment paralleled that observed in the control environment but at a lower plane. Genetic correlations for plasma protein response across aflatoxin levels diminished as the difference between the levels of aflatoxin administered increased. Plasma protein concentration in the control environment was positively correlated with plasma protein response in groups fed a low level of aflatoxin, but negatively correlated when an aflatoxin challenge of 2.5 µg/g or more was given, suggesting that selection for aflatoxin resistance using plasma protein response as a selection criterion should be made under an aflatoxin stress environment.     

Effect of climate and type of storage container on aflatoxin production in corn and its associated risks to wildlife species

The effects of grain storage containers on aflatoxin production, and the relationship between the level of aflatoxin and the number and weight of fluorescing kernels were determined in corn (Zea maize) stored in controlled climate regimes. Two hundred and forty 100-g samples were held up to 3 mos using four types of storage containers placed in four climates. Storage containers included corn placed in metal cans, paper bags, plastic bags, and paper bags placed in plastic bags. Climates were constant during the duration of the project and included a combination of temperatures and humidities. Temperatures were 29-32 C and 14-18 C; relative humidities were 85-88% and 35-40%. In addition, corn was exposed to environmental conditions conductive for aflatoxin production and 100 g samples were randomly collected, examined under ultraviolet light for fluorescence, and then quantified for aflatoxin levels. Corn samples tested negative for aflatoxin at the beginning of the project. Main (i.e., container, climate, and month) and interactive effects were not observed. Mean levels of aflatoxin ranged from 0 to 151 microg/kg. Aflatoxin was produced regardless of type of storage container, time of storage, and climatic conditions; however, only 8% of the samples produced aflatoxin levels that exceeded 50 microg/kg. Fluorescing corn ranged from 0 to 19 kernels per sample, while aflatoxin levels ranged from 0 to 1,375 microg/kg for the same samples. No relationships were found between the number and weight of fluorescing kernels of corn and aflatoxin levels. The black light test yielded a false negative rate of 23% when in fact the aflatoxin concentrations exceeded 50 microg/kg. Therefore, quantifying fluorescing grain under UV light should not be considered a feasible alternative for aflatoxin testing of grain intended for wildlife.     

Aflatoxin levels in corn available as wild turkey feed in Georgia

Samples of corn available as wildlife feed from retailers throughout Georgia (USA) were collected during April 1997 and analyzed for aflatoxin to determine if levels harmful to wild turkeys (Meleagris gallopavo) were present. Three of 31 (10%) samples collected from a 40-country area were positive. An enzyme-linked immunosorbent assay qualitatively determined that two samples contained from 0 to 20 ppb aflatoxin. A chromatography analysis of a third sample measured 380 ppb total aflatoxin. A small percentage of our sample of wildlife feed collected during one season contained levels of aflatoxin that may cause harm to turkeys, especially poults. However, because aflatoxin levels ranging from 100 to 400 ppb may cause liver dysfunction and immunosuppression in turkey poults and other wildlife, grains known to be contaminated with aflatoxin at levels unacceptable for domestic animal feeds (> or =100 ppb) should not be sold as wildlife feed. Further analyses of grains sold as wildlife feed should be conducted to address this potential problem.     

Evaluation of antibody levels during simultaneous aflatoxicosis and vaccination against infectious laryngotracheitis in pullets

Chickens fed 200ppb aflatoxin from 10 days of age were evaluated for their immune response to a modified live infectious laryngotracheitis vaccine. Vaccination was administered at age 4 and 12 weeks. Antibody titers to the vaccine were reduced in chickens given dietary aflatoxin. After 7 weeks, aflatoxin feeding was continued for one month in a treated group and was withdrawn in another. Serology indicated significant differences between the two treated groups relative to whether aflatoxin was fed or not. Significant reduction in body weights, antibody titers and elevated SGOT and SGPT levels were found in chickens treated with aflatoxin. The impact of aflatoxin on reduced body weight, decreased SGOT and SGPT levels and lower antibody titers was shown to be significant in the treated group fed on a ration of aflatoxin until throughout the experiment.     

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.     

Southwestern corn borer (Lepidoptera: Crambidae) damage and aflatoxin accumulation in maize

Aflatoxin, a potent carcinogen, is produced by the fungus Aspergillus flavus Link: Fr. Drought, high temperatures, and insect damage contribute to increased levels of aflatoxin contamination in corn, Zea mays L. Plant resistance is widely considered a desirable method of reducing aflatoxin contamination. Germplasm lines with aflatoxin resistance have been developed. This investigation was undertaken to determine whether crosses among these lines exhibited resistance to southwestern corn borer, Diatraea grandiosella Dyar, and to assess the effects of southwestern corn borer feeding on aflatoxin accumulation. Differences in ear damage among southwestern corn borer infested hybrids were significant. Estimates of general combining ability effects indicated that the lines Mp80:04, Mp420, and Mp488 contributed to reduced ear damage, and SC213 and T165 contributed to greater damage when used in hybrids. Mean aflatoxin levels were 254 ng/g for hybrids infested with southwestern corn borer larvae and 164 ng/g for noninfested hybrids in 2000 when environmental conditions were conducive to aflatoxin production. In contrast, the overall mean aflatoxin level for southwestern corn borer infested hybrids was only 5 ng/g in 1999 when environmental conditions did not favor aflatoxin accumulation. Crosses that included lines selected for aflatoxin resistance as parents (Mp80:04 and Mp313E) exhibited lower levels of aflatoxin contamination both with and without southwestern corn borer infestation in 2000. Only the experimental line Mp80:04 contributed significantly to both reduced southwestern corn borer damage and reduced aflatoxin contamination.     

Metabolism and acute toxicity of aflatoxin B1 in rats

Female rats are more resistant to the acute oral toxicity of aflatoxin B₁ and have higher tissue levels of aflatoxin M₁, a fluorescent hydroxylated metabolite, than males. These differences are reduced by castration, as castrated animals of either sex are more resistant and have higher tissue levels than entire males and females. The toxicity of a single oral dose of aflatoxin B₁ appears to be inversely related to levels of aflatoxin M₁ in the tissues.     

Biocontrol of aflatoxin in corn by inoculation with non-aflatoxigenic Aspergillus flavus isolates

The ability of two non-aflatoxigenic Aspergillus flavus Link isolates (CT3 and K49) to reduce aflatoxin contamination of corn was assessed in a 4-year field study (2001–2004). Soil was treated with six wheat inoculant treatments: aflatoxigenic isolate F3W4; two non-aflatoxigenic isolates (CT3 and K49); two mixtures of CT3 or K49 with F3W4; and an autoclaved wheat control, applied at 20 kg ha^?1. In 2001, inoculation with the aflatoxigenic isolate increased corn grain aflatoxin levels by 188% compared to the non-inoculated control, while CT3 and K49 inoculation reduced aflatoxin levels in corn grain by 86 and 60%, respectively. In 2002, the non-toxigenic CT3 and K49 reduced aflatoxin levels by 61 and 76% compared to non-inoculated controls, respectively. In 2001, mixtures of aflatoxigenic and non-aflatoxigenic isolates had little effect on aflatoxin levels, but in 2002, inoculation with mixtures of K49 and CT3 reduced aflatoxin levels 68 and 37% compared to non-inoculated controls, respectively. In 2003 and 2004, a low level of natural aflatoxin contamination was observed (8 ng g^?1). However, inoculation with mixtures of K49?+?F3W4 and CT3?+?F3W4, reduced levels of aflatoxin 65–94% compared to the aflatoxigenic strain alone. Compared to the non-sclerotia producing CT3, strain K49 produces large sclerotia, has more rapid in vitro radial growth, and a greater ability to colonize corn when artificially inoculated, perhaps indicating greater ecological competence. Results indicate that non-aflatoxigenic, indigenous A. flavus isolates, such as strain K49, have potential use for biocontrol of aflatoxin contamination in southern US corn.     

Induction of aflatoxin biosynthesis inAspergillus parasiticus by ascorbic acid-mediated lipid peroxidation

The effect ofl-ascorbic acid on the biosynthesis of aflatoxin inAspergillus parasiticus was studied. Ascorbic acid at lower concentrations did not inhibit the growth of fungus but markedly induced aflatoxin biosynthesis. At a concentration of 1000 ppm of ascorbic acid, 4.8-fold higher levels of aflatoxin were detected. Copper did not enhance the induction of toxin synthesis by ascorbic acid when added to the growth medium. Ascorbic acid at 1000 ppm was also found to induce aflatoxin synthesis in resting mycelia. Chloroform (1% vol/vol) was found to induce aflatoxin synthesis under similar conditions. Ascorbic acid in the presence of ferrous ion can cause lipid peroxidation, which in turn is responsible for the induction of aflatoxin synthesis. During the induction of aflatoxin synthesis by ascorbic acid, the uptake of carbon source (acetate) was not affected. This observation suggests that on ascorbic acid treatment a precursor or an intermediate of aflatoxin biosynthesis is synthesized in vivo and is responsible for the higher levels of toxin without increasing the uptake of acetate.     

Intrafungal distribution of aflatoxins among conidia and sclerotia of Aspergillus flavus and Aspergillus parasiticus

This research examines the distribution of aflatoxins among conidia and sclerotia of toxigenic strains of Aspergillus flavus Link and Aspergillus parasiticus Speare cultured on Czapek agar (21 days, 28 degrees C). Total aflatoxin levels in conidia and sclerotia varied considerably both within (intrafungal) and among strains. Aspergillus flavus NRRL 6554 accumulated the highest levels of aflatoxin (conidia: B1, 84000 ppb; G1, 566000 ppb; sclerotia: B1, 135000 ppb; G1, 968000 ppb). Substantial aflatoxin levels in conidia could place at risk those agricultural workers exposed to dust containing large numbers of A. flavus conidia. Cellular ratios of aflatoxin B1 to aflatoxin G1 were nearly identical in conidia and sclerotia even though levels of total aflatoxins in these propagule types may have differed greatly. Aflatoxin G1 was detected in sclerotia of all A. flavus strains but in the conidia of only one strain. Each of the A. parasiticus strains examined accumulated aflatoxin G1 in both sclerotia and conidia. These results are examined in the context of current evolutionary theory predicting an increase in the chemical defense systems of fungal sclerotia, propagules critical to the survival of these organisms.     

Effect of malting and roasting on reduction of aflatoxin in contaminated soybeans

The effect of malting and roasting on the reduction of aflatoxin in contaminated soybeans was studied. Through the observation of the malting process of contaminated and noncontaminated beans it was found that aflatoxin brought about 50% reduction on germination percentage and radicle length of malts. Malting appeared to have a minimal effect in lowering the aflatoxin content of the soybean and aflatoxin G-1 was more affected than B-1 by the treatment. The contaminated samples of nonmalted, steeped and malted soybeans were roasted at 150 ° C and 180 ° C. Roasting at 180 ° C reduced the levels of aflatoxin by 40 to 73 percent depending on the sample nature. Roasting of both steeped and malted beans was much less effective in the reduction of the toxin levels than that of nonmalted beans and in all cases aflatoxin B-1 was more heat resistant than aflatoxin G-1.Present address: North Dakota State University, Cereal Chem. & Techn., Fargo, ND 58105, USA     

Aflatoxin variability in pistachios.

Pistachio fruit components, including hulls (mesocarps and epicarps), seed coats (testas), and kernels (seeds), all contribute to variable aflatoxin content in pistachios. Fresh pistachio kernels were individually inoculated with Aspergillus flavus and incubated 7 or 10 days. Hulled, shelled kernels were either left intact or wounded prior to inoculation. Wounded kernels, with or without the seed coat, were readily colonized by A. flavus and after 10 days of incubation contained 37 times more aflatoxin than similarly treated unwounded kernels. The aflatoxin levels in the individual wounded pistachios were highly variable. Neither fungal colonization nor aflatoxin was detected in intact kernels without seed coats. Intact kernels with seed coats had limited fungal colonization and low aflatoxin concentrations compared with their wounded counterparts. Despite substantial fungal colonization of wounded hulls, aflatoxin was not detected in hulls. Aflatoxin levels were significantly lower in wounded kernels with hulls than in kernels of hulled pistachios. Both the seed coat and a water-soluble extract of hulls suppressed aflatoxin production by A. flavus.     

Influence of gamma irradiation of aflatoxin B1 production by Aspergillus flavus growing on some Nigerian foodstuffs

Spores of Aspergillus flavus (UI, 81) inoculated into some local food materials were irradiated at 62.5, 125.0, 250.0 and 500.0 krad, and the effect on aflatoxin B1 production on subsequent incubation was measured. The results show that aflatoxin B1 production decreased with increasing gamma irradiation dose in soya bean, groundnut, palm juice, while paw paw mash showed a relatively high yield of aflatoxin at 125.0 krad as compared to other irradiation levels tested except for the control. Irradiation of soya bean and groundnut inoculated with spores of Aspergillus flavus at 500.0 krad (pre-irradiation incubation period of 2 h) inhibited aflatoxin B1 production. Analysis of variance showed that media, pre-irradiation incubation periods and irradiation levels affected the total amounts of aflatoxin produced.     

Inactivation of aflatoxin B1 by using the synergistic effect of hydrogen peroxide and gamma radiation.

Inactivation of aflatoxin B1 was studied by using gamma radiation and hydrogen peroxide. A 100-krad dose of gamma radiation was sufficient to inactivate 50 micrograms of aflatoxin B1 in the presence of 5% hydrogen peroxide, and 400 krad was required for total degradation of 100 micrograms of aflatoxin in the same system. Degradation of aflatoxin B1 was confirmed by high-pressure liquid chromatographic and thin-layer chromatographic analysis. Ames microsomal mutagenicity test showed loss of aflatoxin activity. This method of detoxification also reduces the toxin levels effectively in artificially contaminated groundnuts.     

Inactivation of aflatoxin B1 by using the synergistic effect of hydrogen peroxide and gamma radiation

Inactivation of aflatoxin B1 was studied by using gamma radiation and hydrogen peroxide. A 100-krad dose of gamma radiation was sufficient to inactivate 50 micrograms of aflatoxin B1 in the presence of 5% hydrogen peroxide, and 400 krad was required for total degradation of 100 micrograms of aflatoxin in the same system. Degradation of aflatoxin B1 was confirmed by high-pressure liquid chromatographic and thin-layer chromatographic analysis. Ames microsomal mutagenicity test showed loss of aflatoxin activity. This method of detoxification also reduces the toxin levels effectively in artificially contaminated groundnuts.     

Correlation of Zn2+ content with aflatoxin content of corn.

Forty-nine samples from the 1983 Virginia corn harvest were analyzed for aflatoxin, zinc, copper, iron, and manganese content. Values (mean +/- standard deviation) were as follows: aflatoxin, 117 +/- 360 micrograms/kg; zinc, 22.5 +/- 3.4 mg/kg; copper, 2.27 +/- 0.56 mg/kg; iron, 40.8 +/- 18.7 mg/kg; and manganese, 5.1 +/- 1.1 mg/kg. Aflatoxin levels positively correlated with zinc (Spearman correlation coefficient, 0.385; P less than 0.006) and copper levels (Spearman correlation coefficient, 0.573; P less than 0.0001). Based on biochemical data in the literature, we believe that the correlation with zinc is important and that there may be a cause-and-effect relationship between zinc levels in corn and aflatoxin levels which are produced upon infection with Aspergillus flavus or A. parasiticus. Control of aflatoxin contamination in field corn by decreasing the zinc levels may be feasible, but no methods to decrease zinc levels are currently available.     

Aflatoxin contamination in insect damaged seeds of horsegram under storage

Studies on one of the protein rich pulses, horsegram (Dolichos biflorus L.) were carried out to know how far these low risk pulses are free from aflatoxin contamination under severe insect infestation in storage. A total of 150 stored seed samples of horsegram were analyzed for the presence of aflatoxins by collecting 25 samples each of undamaged and insect damaged seeds of all the three varieties (PDM-1, PHG-1 and HG-96). More than 33% of insect damaged seed samples were contaminated with aflatoxin B₁ and B₂, whereas less than 8% of the undamaged seed samples contain only low levels of aflatoxin B₂. Higher levels of aflatoxin B₁ (up to 130 μg/kg) were reported in insect damaged seed samples of all the three varieties under study. The levels of aflatoxin B₂ were always lower than aflatoxin B₁ of the corresponding seed samples with insect damage. Aflatoxin B₁ was reported in both the undamaged and insect damaged seed samples of all the three varieties of horsegram. It is evident from the varietal response studies that PDM-1 and HG-96 varieties of horsegram are highly vulnerable to aflatoxin contamination whereas, PHG-1 variety is relatively less susceptible to it. In general, insect infestation leads to increase in fungal invasion (including aflatoxigenic fungi) and this further enhances the levels of aflatoxin contamination in horsegram seeds.     

Factors affecting aflatoxin production by Aspergillus parasiticus in a chemically defined medium

The optimum levels of sucrose, (NH4)2SO4, MgSO4, KH2PO4 and ZnSO4 for aflatoxin production in a chemically defined medium have been established. The last two were found to be essential for fungal growth and aflatoxin production. The effect of various carbon sources on aflatoxin production was tested using the defined medium. Asparagine was found to be essential for aflatoxin production. Very little aflatoxin was produced in the absence of asparagine with any of the other inorganic nitrogen sources tested. Supplementation with yeast extract, Casamino acids, Casitone and peptone increased the aflatoxin yield, but omission of asparagine led to decreased aflatoxin yields even when complex nitrogen sources were present. Asparagine could be replaced by aspartic acid or alanine.     

Effect of pyridazinone herbicides on growth and aflatoxin release by Aspergillus flavus and Aspergillus parasiticus

The influence of pyridazinone herbicides on aflatoxin production by Aspergillus flavus and A. parasiticus was studied in liquid media. Mycelia production was not affected by 20, 40, or 60 micrograms of herbicide per ml; however, aflatoxin production by A. parasiticus was higher in media with herbicide, whereas A. flavus produced lower aflatoxin levels.