Direct visual detection of aflatoxin synthesis by minicolonies of Aspergillus species

Meat Substitute Development from Fungal Protein (Aspergillus oryzae)

The aim of this research is to develop burger patties from fungal protein. For this purpose, to maximize fungal biomass production, an optimization of the growth medium was initially carried out by testing different carbon sources and its proportion with nitrogen. Subsequently, for the design of the fungal patties, the effect of different flours, binders, and colorants on the properties of texture, water retention capacity, and color were tested, with a traditional animal-based burger patty as a control. Based on the first results, two optimal formulations were chosen and analyzed using an electronic tongue with the same control as reference. The conditions that maximized biomass production were 6 days of incubation and maltodextrin as a carbon source at a concentration of 90 g/L. In terms of product design, the formulation containing quinoa flour, carboxymethylcellulose, and beet extract was the most similar to the control. Finally, through shelf-life analysis, it was determined that the physical characteristics of the fungal meat substitute did not change significantly in an interval of 14 days. However, the product should be observed for a longer period. In addition, by the proximate analysis, it was concluded that fungal patties could have nutritional claims such as rich content in protein and fiber.

A risk assessment study of the occurrence and distribution of aflatoxigenic Aspergillus flavus and aflatoxin B1 in dairy cattle feeds in a central northern state, Nigeria

Nigeria, being a tropical nation, characterized by favorable climatic conditions, may display high chances of feed contaminations due to aflatoxigenic Aspergillus flavus with the consequences of health risks associated with the consumption of dairy products. A cross-sectional study was conducted to examine the risks of occurrence and distribution of aflatoxigenic Aspergillus flavus (A. flavus) and aflatoxin B1 (AFB1) contamination levels based on the European Union (EU) and United States Food and Drug Administration (USFDA) set limits. Feeds (n = 144) were collected from selected conventional and traditional dairy herds; prepared and analyzed using immuno-affinity column (IAC) and high performance liquid chromatography (HPLC) respectively. Forty eight (55.8%) isolates were identified as A. flavus of the isolated Aspergilli (n = 86). Of this proportion, 12 (25.0%) were aflatoxigenic strains. An outrageous number of the tested feeds (86.8%, n = 144) were positive for AFB1 contamination. Detectable AFB1 concentrations ranged between (0.5 and 24.8) μgKg^-1 and were distributed variously according to many factors of distribution. Eighty three (66.4%, n = 125) of the AFB1 contaminated feed samples showed AFB1 concentrations between 5 and ≥20 μgKg^-1. All-inclusive policies are key to reducing the health risks posed to the consumers of dairy products.

Aspergillus flavus contamination in two Portuguese wastewater treatment plants

Filamentous fungi from genus Aspergillus were previously detected in wastewater treatment plants (WWTP) as being Aspergillus flavus (A. flavus), an important toxigenic fungus producing aflatoxins. This study aimed to determine occupational exposure adverse effects due to fungal contamination produced by A. flavus complex in two Portuguese WWTP using conventional and molecular methodologies. Air samples from two WWTP were collected at 1 m height through impaction method. Surface samples were collected by swabbing surfaces of the same indoor sites. After counting A. flavus and identification, detection of aflatoxin production was ensured through inoculation of seven inoculates in coconut-milk agar. Plates were examined under long-wave ultraviolet (UV; 365 nm) illumination to search for the presence of fluorescence in the growing colonies. To apply molecular methods, air samples were also collected using the impinger method. Samples were collected and collection liquid was subsequently used for DNA extraction. Molecular identification of A. flavus was achieved by real-time polymerase chain reaction (RT-PCR) using the Rotor-Gene 6000 qPCR detection system (Corbett). Among the Aspergillus genus, the species that were more abundant in air samples from both WWTP were Aspergillus versicolor (38%), Aspergillus candidus (29.1%), and Aspergillus sydowii (12.7%). However, the most commonly species found on surfaces were A. flavus (47.3%), Aspergillus fumigatus (34.4%), and Aspergillus sydowii (10.8%). Aspergillus flavus isolates that were inoculated in coconut agar medium were not identified as toxigenic strains and were not detected by RT-PCR in any of the analyzed samples from both plants. Data in this study indicate the need for monitoring fungal contamination in this setting. Although toxigenic strains were not detected from A. flavus complex, one cannot disregard the eventual presence and potential toxicity of aflatoxins.

Solid-supported room temperature phosphorescence from aflatoxins for analytical detection of Aspergillus spp. strains

A simple, direct and rapid analytical methodology for the detection of aflatoxin producing Aspergillus spp. strains based on the measurement of room temperature phosphorescence from aflatoxins is presented here.

Yellow pigments used in rapid identification of aflatoxin-producing Aspergillus strains are anthraquinones associated with the aflatoxin biosynthetic pathway

Studies on biological control of aflatoxin production in crops by pre-infection with non-toxigenic Aspergillus flavus strains have created a need for improved methods to screen isolates for aflatoxigenicity. We have evaluated two empirical aflatoxigenicity tests: (i) yellow pigment production, and (ii) the appearance of a plum-red color in colonies exposed to ammonium hydroxide vapor. Yellow pigments from aflatoxigenic A. flavus were shown to function as pH indicator dyes. Seven pigments representing most of the pigmentation in extracts have been isolated using color changes when chromatography spots were exposed to ammonium hydroxide vapor to guide fractionation. Their structures have been shown to be norsolorinic acid, averantin, averufin, versicolorin C, versicolorin A, versicolorin A hemiacetal and nidurufin, all of which are known anthraquinone pigments on, or associated with, the aflatoxin biosynthetic pathway in Aspergillus spp. Thus, the basis of both empirical tests for aflatoxigenicity is detecting production of excess aflatoxin biosynthetic intermediates.

An isolate of Aspergillus flavus used to reduce aflatoxin contamination in cottonseed has a defective polyketide synthase gene

Contamination of certain foods and feeds with the highly toxic and carcinogenic family of Aspergillus mycotoxins, the aflatoxins, can place a severe economic burden on farmers. As one strategy to reduce aflatoxin contamination, the non-aflatoxin-producing A. flavus isolate AF36 is currently being applied to agricultural fields to competitively exclude aflatoxin-producing Aspergillus species. We now show that the polyketide synthase gene (pksA) required for aflatoxin biosynthesis in AF36, and in other members of the same vegetative compatibility group, possesses a nucleotide polymorphism near the beginning of the coding sequence. This nucleotide change introduces a premature stop codon into the coding sequence, thereby preventing enzyme production and aflatoxin accumulation.

Comparison of cultural and analytical methods for determination of aflatoxin production by Mississippi DeltaAspergillusisolates

This study compared cultural and analytical methods for detecting aflatoxin production by Aspergillus species. Aspergillus isolates were obtained from various Mississippi Delta crops (corn, peanut, rice, cotton) and soils. Most of the isolates (99%) were A. flavus and the remainder comprised A. parasiticus and A. nomius. The following three cultural methods were evaluated on potato dextrose agar: fluorescence (FL) on β-cyclodextrin-containing media (CD), yellow pigment (YP) formation in mycelium and medium, and color change after ammonium hydroxide vapor exposure (AV). Aflatoxins in culture extracts were confirmed by thin-layer chromatography (TLC) and quantified by enzyme-linked immunosorbent assay (ELISA). Of the 517 isolates, 314 produced greater than 20 ng/g of total aflatoxin based on ELISA, and 180 produced greater than 10 000 ng/g of aflatoxin in the medium. Almost all the toxigenic isolates (97%) were confirmed by TLC as producers. Of the toxigenic isolates, as determined by ELISA, 93%, 73%, and 70% gave positive FL, YP, and AV responses, respectively. Of the 203 isolates producing less than 20 ng/g of aflatoxin, 20%, 6%, and 0% of respective FL, YP, and AV methods gave false-positive responses. The 9% false-positive results from TLC fall within this range. This study showed good agreement among all tested cultural methods. However, these cultural techniques did not detect aflatoxin in all cultures that were found to produce aflatoxins by ELISA, LC/MS, and TLC. The best results were obtained when the AV color change and CD fluorescence methods were used together, yielding an overall success rate comparable to TLC but without the need for chemical extraction and the time and expense of TLC.Key words: aflatoxins, analytical methods, Aspergillus flavus, Aspergillus parasiticus, cultural methods, β-cyclodextrin, fluorescence enhancers, mycotoxins, yellow pigment.

Application of a modified culture medium for the simultaneous counting of molds and yeasts and detection of aflatoxigenic strains of Aspergillus flavus and Aspergillus parasiticus

Molds and yeasts from 91 samples of feed and raw materials used in feed formulation were enumerated on a new culture medium to which a beta cyclodextrin (beta-W7M 1.8-cyclodextrin) had been added. This medium was compared with other media normally used in laboratories for the routine analysis of fungi, such as Sabouraud agar, malt agar supplemented with 2% dextrose, and potato dextrose agar. When a t test for paired data (0.05 significance level, 95% confidence interval) was applied, no statistically significant differences between the results obtained with the new culture medium and those obtained with the other media used to enumerate molds and yeasts were found. For the evaluation of contamination due to aflatoxin for all of the samples, Sabouraud agar and yeast extract agar, both supplemented with 0.3% beta-W7M 1.8-cyclodextrin, and APA (aflatoxin-producing ability) medium were used. Aflatoxin was detected in 21% of the feed samples and in 23% of the raw-material samples analyzed, with maximal amounts of 2.8 and 6.0 microg of aflatoxin B1 per kg, respectively, being detected. In any case, the aflatoxin contents found exceeded the legally stipulated limits. The t test for paired data (0.05 significance level, 95% confidence interval) did not show statistically significant differences between the results obtained with the different culture media used for the detection of aflatoxins. The advantage of the new medium developed (Sabouraud agar with 0.3% beta-W7M 1.8-cyclodextrin) is that it allows simultaneous fungal enumeration and determination (under UV light) of the presence of aflatoxin-producing strains without prior isolation and culture procedures involving expensive and/or complex specific media and thus saves work, time, and money.

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.

Differentiation of aflatoxin-producing and non-producing strains of Aspergillus flavus group

AIMS

Three conventional methods and a multiplex PCR procedure with a set of four primers (Quadruplex-PCR) were used to differentiate between aflatoxin-producing and non-producing strains of the Aspergillus flavus group.

METHODS AND RESULTS

By combining sets of primers for aflR, nor-1, ver-1 and omt-A genes of the aflatoxin biosynthetic pathway, Quadruplex-PCR showed that aflatoxinogenic strains gave a quadruplet pattern, indicating the presence of all the genes involved in the aflatoxin biosynthetic pathway which encode for functional products. Non-aflatoxinogenic strains gave varying results with one, two, three or four banding patterns. A banding pattern in three non-aflatoxinogenic strains resulted in non-differentiation between these and aflatoxinogenic strains.

CONCLUSION AND SIGNIFICANCE AND IMPACT OF THE STUDY

Because conventional methods are time-consuming, further studies are needed to develop a rapid and objective technique that permits complete differentiation between aflatoxin-producing and non-producing strains of the A. flavus group.

Use of propolis and ultragriseofulvin to inhibit aflatoxigenic fungi

Propolis ethanolic extract (PEE) at 3 and 4 g/L and ultragriseofulvin (UG) at 0.75 and 1 g/L reduced the percentage of conidia germination in two Aspergillus flavus isolates. PEE at 1-4 g/L decreased the mycelial dry mass of A. flavus isolates by 11-80%, and aflatoxin B1 production by 34-100%. UG concentrations of 0.25-1 g/L reduced the growth and aflatoxin B1 production of the isolates by 16-88 and 48-98%, respectively. Any increase in PEE and UG concentration was accompanied by a clear decrease in the per cent conidia germination, growth and aflatoxin B1 production. At equal concentration, UG was about 4-times more effective than PEE.

Incidence and stability of infection by double-stranded RNA genetic elements inAspergillussectionflaviand effects on aflatoxigenicity

Ninety-two isolates belonging to Aspergillus sect, flavi were analyzed for double-stranded (ds) RNA via standard cellulose chromatography. Double-stranded RNA infection was detected in fungal isolates that had been in culture for long periods (5 of 26 were infected) and in those recently isolated (5 of 66 were infected). The number of dsRNA genetic elements differed among infected isolates and no two isolates contained identical dsRNAs on the basis of electrophoretic migration in agarose gels. Addition of micronutrients to culture media affected both the amount of dsRNA produced and the number of dsRNA genetic elements detected. Attempts to cure six fungal isolates of dsRNA by serial single conidial transfer, chlorate selection for nitrogen-metabolism mutants, and cycloheximide treatment, met with variable results. The frequency at which serial single conidial transfer and nitrogen-metabolism mutant (nit) selection successfully cured six Aspergillus sect, flavi isolates varied from 11 to 100% and 0 to 100%, respectively. The cycloheximide treatment was effective at curing 40% of the dsRNA-infected isolates. Comparison of aflatoxin production prior to and after dsRNA curing indicated that infection by dsRNA did not influence aflatoxin production. However, aflatoxin production by two isolates (91-031B and 91-184G) was reduced by both single conidial transfer and induction of nit mutants. Keywords: aflatoxin, cycloheximide, mycovirus, nitrogen-metabolism mutant.