Aflatoxin-Producing Strains Of Aspergillus Flavus Research Articles

Effects of temperature and relative humidity on Aflatoxin B1 reduction in corn grains and antagonistic activities against Aflatoxin-producing Aspergillus flavus by a volatile organic compound-producing yeast, Kwoniella heveanensis DMKU-CE82

As shown in our previous study, Kwoniella heveanensis DMKU-CE82, a volatile organic compound (VOC)-producing yeast, demonstrated promising antagonistic activity against aflatoxin-producing strain of Aspergillus flavus. This yeast’s volatile organic compounds (VOCs) could reduce Aflatoxin B1 (AFB1) in corn grains. In the current study, we evaluated the effect of temperatures and relative humidity on AFB1 reduction during grain storage when co-incubated with this VOC-producing yeast. The VOCs produced by K. heveanensis DMKU-CE82 could promote reduction of AFB1 to less than 20 part per billion (ppb) in the fungal contaminated corn grains under most storage conditions at 35 °C. The major VOCs produced by 2-, 4-, and 6-day-old yeast cultures were closely matched to 3-methyl-1-butanol, 2-methyl-1-butanol, hydrazine-1-1-dimethyl, and butanoic acid-3-methyl. In addition, this yeast strain had the ability to produce β-1,3-glucanase, amylase, cellulase, chitinase, siderophores, and biofilms. Scanning electron microscopy also confirmed the antagonistic activity of K. heveanensis DMKU-CE82 as it caused structural damage to conidia and inhibited the development of mycelia and conidiophores in both direct fungal–yeast interaction and the VOC method in corn grains. These results demonstrated that this yeast strain could be a promising biocontrol agent against aflatoxin-producing fungi in agricultural products.

Systemic aspergillosis caused by an aflatoxin-producing strain of Aspergillus flavus

The first case of human systemic infection by an Aspergillus flavus isolate demonstrated to produce aflatoxins in vitro and in vivo is described. The patient, a 41-year-old man with acute myelogenous leukaemia, developed a complication of suspected pulmonary Aspergillus infection during remission induction therapy. Antifungal chemotherapy brought about a considerable degree of improvement, but remission of the underlying disease was not attained. Bone marrow transplantation was also not effective. The patient showed recovery from neutropenia but died despite aggresive antifungal chemotherapy. The autopsy revealed lesions in the lungs, myocardium, kidneys, brain, thyroid gland and skin due to a suspected Aspergillus sp. A fungus isolated from the right lung and the skin lesions was identified as A. flavus. Aflatoxins B1, B2 and M1 were detected in culture filtrates of the isolated A. flavus, and in an extract of lung lesions. These aflatoxins are considered to have played an important role in damaging the immune system of the patient through their toxic effects.

A rapid identification method for aflatoxin-producing strains of Aspergillus flavus and A. parasiticus by ammonia vapor

The colony reverse of aflatoxin (AF)-producing strains of Aspergillus flavus and A. parasiticus turned pink when their cultures were exposed to ammonia vapor. The color change was visible for colonies grown on media suitable for AF production such as potato dextrose, coconut, and yeast extract sucrose agars after 2 d incubation at 25°C. Of the 120 strains of A. flavus, A. parasiticus, and two related species in A. flavus group: A. oryzae and A. sojae tested in this study, only the AF-producing strains of A. flavus and A. parasiticus showed the pink pigmentation. The color change occurred immediately after the colony was contacted with ammonia vapor. This method was useful for rapid screening the AF-producing strains of A. flavus and A. parasiticus.

Systemic aspergillosis caused by an aflatoxin-producing strain of Aspergillus flavus

Systemic aspergillosis caused by an aflatoxin-producing strain of Aspergillus flavus

Aflatoxin-Producing Strains of Aspergillus flavus Isolated from Cheese

Contamination by fungi of the genus Aspergillus with special reference to the possible detection of aflatoxin-producing strains of Aspergillus flavus was studied in 52 samples of commercial cheeses made with different types of milk (8 of cow's milk, 12 of ewe's milk, 13 of goat's milk, and 19 of milk mixtures of various species: cow, ewe, and goat) produced in Southern Spain. The frequency of appearance of various species of Aspergillus, A. glaucus, A. niger, A. nidulans, A. sulphureus, A. Terreus, and A. flavus, in the different types of cheese was determined. In 4 (2 of goat's milk cheese and 2 of cheeses made with milk from various species) out of 52 samples (7.69%), aflatoxin-producing strains of A. flavus were detected.

Aflatoxin-producing strains of Aspergillus flavus in the mould flora of the different greenhouse substrates for the cultivation of cucumber ( Cucumis sativus, L.)

Fungal contamination in a greenhouse for production of cucumbers ( Cucumis sativus L.) was studied. 158 samples of water, sand, air, leaves and fruits were analyzed. 25 different genera were isolated, the most frequent ones being Pullularia, Aspergillus, Paecilomyces, Alternaria, Fusarium, Rhizopus and Penicillium. Pullularia, Aspergillus, Paecilomyces and Penicillium were present in all types of samples studied. Twenty-one strains of A. flavus were identified and only eight of those produced aflatoxins “in vitro”.

Aflatoxin-Producing Strains of Aspergillus flavus in Yogurt

Fungal contamination was investigated in two batches of commercial yogurt obtained from two different Spanish manufacturers, with special reference to the detection of aflatoxin-producing strains of Aspergillus. The samples were classified into four grades of standard, according to the level of mold present: target, acceptable, doubtful, and reject. The frequency of appearance of different genera of molds in yogurt was also determined. Species of Aspergillus, potential producers of mycotoxins, were frequently identified in the samples analyzed. In seven out of 20 samples (35%), aflatoxin-producing strains of Aspergillus flavus were detected.

Precipitins to an aflatoxin-producing strain of Aspergillus flavus in patients with malignancy.

Serum samples from 121 patients in whom malignant disease had been diagnosed, were assayed for precipitins to fungal isolates from leukemia-associated environments. Control sera were from age-, sex-, and race-matched patients with no history of malignant disease. Sera from 36 (30%) malignancy patients and seven (6%) controls yielded a precipitin band to an aflatoxin-producing Aspergillus flavus isolate from a leukemia-associated house (x2 = 222, p less than 0.05%). No significant numbers of precipitins were obtained to either of the other fungal isolates from that and another such house. Although A. fumigatus has frequently been incriminated as a source of infection in patients with malignancy, only 9% of malignancy patients had a precipitin response to it, as did 1.6% of controls. Also, the presence of the precipitins to A. flavus was not connected with past radiation or immunosuppressive therapy. However, among patients with precipitins to A. fumigatus there was a higher death rate in the year following the study. Precipitins to A. flavus may be related to heavy environmental exposure possibly leading to aflatoxin exposure which may contribute to development of malignancy though immunosuppressive effects.

Use of aflatoxin-producing ability medium to distinguish aflatoxin-producing strains of Aspergillus flavus.

Aflatoxin-producing ability medium was tested for its ability to distinguish aflatoxin-positive from aflatoxin-negative strains of Aspergillus flavus in naturally occurring populations from corn at harvest. All of the aflatoxin-positive strains and some of the aflatoxin-negative strains produced aflatoxins when cultured on cracked corn. Although the data indicate that aflatoxin-producing ability medium is not entirely reliable in distinguishing potential aflatoxin-producing strains of A. flavus from nontoxigenic strains, it is significant that the medium did not yield false-positives.

Influence of Diurnal Temperature Cycles on Infection of Cotton Bolls by Aspergillus flavus

Excised cotton bolls were inoculated with an aflatoxin-producing strain of Aspergillus flavus (ATCC #26994), and were placed in growth chambers for 7 or 3 days with short (2-hour) or long (10-hour) diurnal maximum temperature cycles. The maximum and minimum temperatures were 30-32 C and 16-18 C, respectively. The percent bright greenish-yellow (BGY) fluorescence of locks and seeds, as well as seed infection of BGY-fluorescent seeds, increased as the duration of the daily maximum temperature of 30 C increased, and/or as the number of diurnal maximum temperature cycles of 30 C increased. Aflatoxin did not accumulate in A. flavus-infected seed, regardless of treatment.

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.

Laboratory Studies on the Formation of Aflatoxin in Forages

SUMMARYForages are often subjected to fungus growth both in storage and in the field and, therefore, may be contaminated with aflatoxin. Aflatoxin-producing strains of Aspergillus flavus were used to inoculate flasks containing moistened forages. The fungus grew well, causing considerable disintegration of the plant material. The fermented forages were extracted with chloroform for assay, and impurities were removed from extract residues by precipitation from 70% acetone solutions with lead acetate and with hexane from chloroform solutions. Partially purified extracts were chromatographed on thin-layer plates and quantities of aflatoxin determined with a recording densitometer. All forages at 6 days showed the presence of aflatoxin, except red clover and alfalfa. All strains formed aflatoxin on timothy, sweet clover, and oat straw. Aflatoxin B1 was produced at levels of 18–52 μg/g by NRRL 3145 on sweet clover and oat straw. The highest total aflatoxin (170 μg/g) was on oat straw fermented with NRRL 3145, as well as the highest yields of G1, 108 μg. Results were confirmed with the duckling assay.