Highly sensitive PCR-based detection method specific forAspergillus flavusin wheat flour

Simultaneous detection of mycotoxigenic Aspergillus species of sections Circumdati and Flavi using multiplex digital PCR

Populations of ochratoxin-producing Aspergillus section Circumdati species and aflatoxin-producing Aspergillus section Flavi species frequently coexist in soil and are the main sources of mycotoxin contamination of tree nuts. Identification of mycotoxigenic Aspergillus species in these sections is difficult using traditional isolation and culture methods. We developed a multiplex digital PCR (dPCR) assay to detect and quantify Aspergillus ochraceus, Aspergillus westerdijkiae, and Aspergillus steynii (section Circumdati), as well as Aspergillus flavus and Aspergillus parasiticus (section Flavi), in environmental samples based on species-specific calmodulin gene sequences. Relative quantification of each species by dPCR of mixed-species templates correlated with corresponding DNA input ratios. Target species could be detected in soil inoculated with conidia from each species. Non-target species of sections Circumdati, Flavi, and Nigri were generally not detectable using this dPCR method. Detected non-target species (Aspergillus fresenii, Aspergillus melleus, Aspergillus sclerotiorum, and Aspergillus subramanianii) were discernible from A. ochraceus in dual-template dPCR reactions based on differential fluorescence intensity.

Development of a real-time PCR and multiplex PCR assay for the detection and identification of mycotoxigenic fungi in stored maize grains

This study aimed to identify important mycotoxigenic fungi and accurate detection of mycotoxin in stored maize grains using molecular methods. The current study also optimised the real-time PCR (RT-PCR) assay. The melting curve was established to identify isolated fungal species of Aspergillus (4), Fusarium (3), Penicillium (3), and Alternaria (one). A multiplex polymerase chain reaction (mPCR) technique was developed for the detection and characterisation of mycotoxin producing fungi, mycotoxin metabolic pathway genes, and the determination of eleven mycotoxins in stored maize grains using high-performance liquid chromatography (HPLC). The mPCR results indicated positive signals for potentially mycotoxigenic fungal species tested of Aspergillus, Fusarium, Penicillium, and Alternaria. A protocol for multiplex reverse transcription-polymerase chain reaction (mRT-PCR) was tested to distinguish between free and contaminated, stored maize with aflatoxin B1 (AFB1). The expression pattern of four aflatoxin biosynthetic pathway genes, AFB1 (aflQ, aflP, aflO, and aflD), was a good marker for contaminated, stored maize grains. HPLC analysis showed that maize grain samples were contaminated with mycotoxins, and the concentration was above the detection level. The results indicate that the polyphasic approach might provide a sensitive, rapid, and accurate method for detecting and identifying mycotoxigenic fungal species and mycotoxins in stored maize grains.

Conventional and advanced detection techniques of foodborne pathogens: A comprehensive review

Foodborne pathogens are a major public health concern and have a significant economic impact globally. From harvesting to consumption stages, food is generally contaminated by viruses, parasites, and bacteria, which causes foodborne diseases such as hemorrhagic colitis, hemolytic uremic syndrome (HUS), typhoid, acute, gastroenteritis, diarrhea, and thrombotic thrombocytopenic purpura (TTP). Hence, early detection of foodborne pathogenic microbes is essential to ensure a safe food supply and to prevent foodborne diseases. The identification of foodborne pathogens is associated with conventional (e.g., culture-based, biochemical test-based, immunological-based, and nucleic acid-based methods) and advances (e.g., hybridization-based, array-based, spectroscopy-based, and biosensor-based process) techniques. For industrial food applications, detection methods could meet parameters such as accuracy level, efficiency, quickness, specificity, sensitivity, and non-labor intensive. This review provides an overview of conventional and advanced techniques used to detect foodborne pathogens over the years. Therefore, the scientific community, policymakers, and food and agriculture industries can choose an appropriate method for better results.

Low-cost, specific PCR assays to identify the main aflatoxigenic species of Aspergillus section Flavi

Aflatoxins are fungal metabolites that are present as contaminants in food globally. Most aflatoxigenic species belong to Aspergillus section Flavi, and the main ones are grouped in the A. flavus clade, where many cryptic species that are difficult to discriminate are found. In this study, we investigated inter- and intraspecific diversity of the A. flavus clade to develop low-cost, species-specific PCR assays for identifying aflatoxigenic species. A total of 269 sequences of the second largest subunit of RNA polymerase II (RPB2) locus were retrieved from GenBank, and primer pairs were designed using data mining to identify A. flavus, A. parasiticus, and A. novoparasiticus. Species-specific amplicons of approximately 620, 350, and 860 bp enabled identification of target species as A. flavus, A. parasiticus, and A. novoparasiticus, respectively.

Sensitivity of Aspergillus flavus Isolates from Peanut Seeds in Georgia to Azoxystrobin, a Quinone outside Inhibitor (QoI) Fungicide

Aspergillus flavus infects peanuts and produces a mycotoxin called aflatoxin, a potent human carcinogen. In infected peanuts, it can also affect peanut seed quality by causing seed rot and reducing seed viability, resulting in low germination. In 2020, peanut seeds in Georgia had lower than expected germination and a high frequency of A. flavus contamination. A total of 76 Aspergillus isolates were collected from seven seed lots and their identity and in vitro reaction to QoI (quinone outside inhibitor) fungicide (azoxystrobin) were studied. The isolates were confirmed as A. flavus by morphological characteristics and a PCR (polymerase chain reaction)-based method using species-specific primers. In vitro, these isolates were tested for sensitivity to azoxystrobin. The mean EC50 values ranged from 0.12 to 297.22 μg/mL, suggesting that some isolates were resistant or tolerate to this fungicide. The sequences of cytochrome b gene from these isolates were compared and a single nucleotide mutation (36.8% isolates) was found as Cyt B G143A, which was associated with the total resistance to the QoIs. Another single mutation (15.8% isolates) was also observed as Cyt B F129L, which had been documented for QoI resistance. Therefore, a new major single mutation was detected in the A. flavus natural population in this study, and it might explain the cause of the bad seed quality in 2020. The high frequency of this new single nucleotide mutation exists in the natural population of A. flavus and results in the ineffectiveness of using azoxystrobin seed treatment. New seed treatment fungicides are needed.

Molecular characterization of ochratoxigenic fungi associated with poultry feedstuffs in Saudi Arabia

Fungal and mycotoxins contamination of food and poultry feeds can occur at each step along the chain from grain production, storage, and processing. A total of 200 samples comprising of mixed poultry feedstuffs (n = 100) and their ingredients (n = 100) were collected from Riyadh, Alhassa, Qassium, and Jeddah cities in Saudi Arabia. These samples were screened for contamination by fungi. Penicillium chrysogenum was the predominant species taking into its account and frequency, respectively, in both mixed poultry feedstuff and barley samples (4,561.9 and 687 fungal colony-forming units (CFU)/g) and (66% and 17%). Moisture content was an important indicator for the count of fungi and ochratoxin A. Ochratoxin analysis of plate cultures was performed by a HPLC technique. Sample of mixed poultry feedstuff which was collected from Jeddah displayed the highest level of ochratoxin (14.8 µg/kg) and moisture content (11.5%). Corn grains samples were highly contaminated by ochratoxin A (450 and 423 µg/kg) and recorded the highest moisture contents (14.1 and 14.5%). Ochratoxin A production in fungal species isolated from mixed poultry feedstuff samples were high with P. verrucosum (5.5 μg/kg) and A. niger (1.1 μg/kg). In sorghum and corn grains, the highest ochratoxins producing species were P. viridicatum (5.9 μg/kg) and A. niger (1.3 μg/kg), respectively. Sixty-three isolates of A. niger were ochratoxigenic, and all of them showed the presence of pks genes using PKS15C-MeT and PKS15KS primer pairs. The detection technique of A. niger in poultry feedstuff samples described in the present study was successfully used as a rapid and specific protocol for early detection of A. niger without cultivation on specific media.

Morphological and Molecular Characterization of Toxigenic Aspergillus flavus from Groundnut Kernels in Kenya

Pathogenesis of Aspergillus flavus on important agricultural products is a key concern on human health due to the synthesis and secretion of the hazardous secondary metabolite, aflatoxin. This study identified and further characterized aflatoxigenic A. flavus from groundnuts sampled from sundry shops in Kenya using integrated morphological and molecular approaches. The groundnuts were plated on potato dextrose agar for isolation and morphological observation of A. flavus based on macroscopic and microscopic features. Molecular characterization was done through amplification and comparison of the partial sequence of the ITS1-5.8S-ITS2 region. The expression analysis of aflR, aflS, aflD, aflP, and aflQ genes in the aflatoxin biosynthesis pathways was conducted to confirm the positive identification of A. flavus. The gene expression also aided to delineate toxigenic isolates of A. flavus from atoxigenic ones. Morphologically, 18 isolates suspected to be A. flavus were identified. Out of these, 14 isolates successfully amplified the 500 bp ITS region of A. flavus or Aspergillus oryzae, while 4 isolates were not amplified. All the remaining 14 isolates expressed at least one of the aflatoxigenic genes but only 5 had all the genes expressed. Partial sequencing revealed that isolates 5, 11, 12, 13, and 15 had 99.2%, 97.6%, 98.4%, 97.5%, and 100% homology, respectively, to the A. flavus isolate LUOHE, ITS-5.8S-ITS2, obtained from the NCBI database. The five isolates were accurate identification of atoxigenic A. flavus. Precise identification of toxigenic strains of A. flavus will be useful in establishing control strategies of the fungus in food products.

Multiplex PCR assay to detect Aspergillus, Penicillium and Fusarium species simultaneously

A wide variety of mycotoxins is produced by mycotoxigenic fungi and naturally contaminates food and feed products worldwide. Synergistic effects of multi-toxins are potentially more harmful than exposure to a single compound and can induce acute and chronic toxicity to animals and humans. The aim of the present study is to timely and simultaneously identify the multiple mycotoxigenic fungi capable of causing synergistic toxicity to improve the safety level of food and feedstuff. Here, a multiplex polymerase chain reaction assay was developed for simultaneous detection of mycotoxigenic fungi belonging to the genera Aspergillus, Fusarium and Penicillium. Three pairs of genus-specific primers were designed based on internal transcribed spacer (ITS) sequences of Aspergillus and Penicillium, and Elongation factor 1 alpha (EF- 1α) of Fusarium. Amplicons of 170, 750 and 490 bp respectively for the corresponding primer pairs were detected; thus amplicon length is diagnostic for the individual fungal genus. The sensitivity of the developed method was tested with genomic DNA obtained from mould pure cultures and artificially contaminated maize grain powder. The sensitivity result showed that spore concentrations in the contaminated maize grain powder of 10² spores/mL were detected without prior incubation. This result suggests that the developed mPCR assay would allow a rapid, specific and simultaneous detection of various mycotoxigenic potential fungi based on the occurrence and size of the amplification products and thus to estimate the multi-mycotoxins contamination potential in food and feedstuff.

Assessment of the Effect of Satureja montana and Origanum virens Essential Oils on Aspergillus flavus Growth and Aflatoxin Production at Different Water Activities

Aflatoxin contamination of foodstuffs poses a serious risk to food security, and it is essential to search for new control methods to prevent these toxins entering the food chain. Several essential oils are able to reduce the growth and mycotoxin biosynthesis of toxigenic species, although their efficiency is strongly influenced by the environmental conditions. In this work, the effectiveness of Satureja montana and Origanum virens essential oils to control Aspergillus flavus growth was evaluated under three water activity levels (0.94, 0.96 and 0.98 a_w) using a Bioscreen C, a rapid in vitro spectrophotometric technique. The aflatoxin concentrations at all conditions tested were determined by HPLC-FLD. Aspergillus flavus growth was delayed by both essential oil treatments. However, only S. montana essential oil was able to significantly affect aflatoxin production, although the inhibition percentages widely differed among water activities. The most significant reduction was observed at 0.96 a_w, which is coincident with the conditions in which A. flavus reached the highest levels of aflatoxin production. On the contrary, the treatment with S. montana essential oil was not effective in significantly reducing aflatoxin production at 0.94 a_w. Therefore, it is important to study the interaction of the new control compounds with environmental factors before their application in food matrices, and in vitro ecophysiological studies are a good option since they provide accurate and rapid results.

A Comprehensive Study on the Occurrence of Mycotoxins and Their Producing Fungi during the Maize Production Cycle in Spain

Mycotoxin contamination is one of the main problems affecting corn production, due to its significant risk to human and animal health. The Fusarium and Aspergillus species are the main producers of mycotoxins in maize, infecting both pre-harvest and during storage. In this work, we evaluated the presence of mycotoxins and their producing species along maize production cycles in three different stages (anthesis, harvest, and storage) during three consecutive seasons (2016-2018). Fungal occurrences were studied using species-specific PCR protocols, whereas mycotoxin levels were determined by LC-MS/MS. Fumonisin-producing Fusarium species (F. verticillioides and F. proliferatum), as well as the aflatoxin producer Aspergillus flavus, were the most predominant species at all stages; although, during some seasons, the presence of F. graminearum and A. niger aggregate species were also identified. Contrastingly, fumonisins were the only mycotoxins detected and levels were always under legal regulations. The results presented here demonstrate that even when fungal contamination occurs at the early stages of the maize production cycle, the application of good agricultural and storage practices might be crucial to ensure mycotoxin-free grains.

A Novel Niosome-Encapsulated Essential Oil Formulation to Prevent Aspergillus flavus Growth and Aflatoxin Contamination of Maize Grains During Storage

Aflatoxin (AF) contamination of maize is a major concern for food safety. The use of chemical fungicides is controversial, and it is necessary to develop new effective methods to control Aspergillus flavus growth and, therefore, to avoid the presence of AFs in grains. In this work, we tested in vitro the effect of six essential oils (EOs) extracted from aromatic plants. We selected those from Satureja montana and Origanum virens because they show high levels of antifungal and antitoxigenic activity at low concentrations against A. flavus. EOs are highly volatile compounds and we have developed a new niosome-based encapsulation method to extend their shelf life and activity. These new formulations have been successfully applied to reduce fungal growth and AF accumulation in maize grains in a small-scale test, as well as placing the maize into polypropylene woven bags to simulate common storage conditions. In this latter case, the antifungal properties lasted up to 75 days after the first application.

Aptamer as capture agent in enzyme-linked apta-sorbent assay (ELASA) for ultrasensitive detection of Aflatoxin B1

Aflatoxin B₁ (AFB₁), is one of the most toxic mycotoxins found to contaminate various food commodities like cereals, dried fruits, tree nuts, spices and crude vegetable oils. In spite of considerable progress in analytical techniques, there is still a need to develop rapid and highly sensitive detection platforms for AFB₁. In this study, AFB₁ specific aptamer was used as a capture molecule to develop an enzyme-linked apta-sorbent assay (ELASA) for ultrasensitive detection of AFB₁. Under optimized conditions, the assay had a linear detection range from 1 μg to 1 pg with a limit of detection (LOD) of 1 pg/mL in buffer. Conventional ELISA with AFB₁ hapten as the capture agent (LOD = 10 pg/mL) was also carried out to compare the results with the present method. Recovery studies in food samples like dried red chillies, groundnut and pepper using both the methods was found to be in the range of 88.49-106.4% at 10 ng/mL and 87.4% to 95.8% at 5 ng/mL for ELASA and 76.56-127.68% at 10 ng/mL and 82-101.2% at 5 ng/mL for ELISA. Higher detection (10 fold) and better recovery using ELASA suggest that the method could offer an early, ultrasensitive, high-throughput, qualitative and semi-quantitative detection of AFB₁ in contaminated food samples.

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.

Versicolorin A is a potential indicator of aflatoxin contamination in the granary-stored corn

The objective of this study was to evaluate the feasibility of the predictive monitoring of aflatoxin B₁ (AFB₁) under granary conditions, since mycotoxin contamination of the stored grain represents an important issue. Using the storage test, we investigated the relationship between versicolorin A (Ver A, an intermediate in AFB₁ biosynthesis) levels and the levels of aflatoxigenic fungi, and their relationship with aflatoxin production. All samples, except for one, were found to be contaminated with aflatoxigenic fungi using PCR analyses, while their AFB₁ levels were not detectable before the storage test using an enzyme-linked immunosorbent assay (ELISA) method with an LOD of 2 μg/kg. Aflatoxigenic fungi levels were analysed, as well as Ver A levels prior to the accumulation of AFB₁ (Levels were ≥5 μg/kg; the permissible levels of AFB₁ in corn intended for direct consumption are <5 μg/kg (EC)). Statistical analyses demonstrated that aflatoxin levels after both actual storage and safe storage (AFB₁˂5μg/kg) times are significantly correlated with the Ver A levels and the changes in Ver A levels (ΔVer A). Both high and variable Ver A levels were indicative of the vigorous metabolic activity of aflatoxigenic fungi. In contrast, steady Ver A levels showed that aflatoxin production by the fungi was not active. Monitoring Ver A levels and their changes may allow an earlier detection of harmful aflatoxin contamination in the stored grain. Additionally, the toxicity of Ver A should be further examined. The results of our study indicate that the monitoring of Ver A levels, even when the AFB₁ levels are very low, may increase the safety of grain consumption, especially considering Ver A toxicity.

Optimal pcr primers for rapid and accurate detection of Aspergillus flavus isolates

Aspergillus flavus is among the most devastating opportunistic pathogens of several food crops including rice, due to its high production of carcinogenic aflatoxins. The presence of these organisms in economically important rice strip farming is a serious food safety concern. Several polymerase chain reaction (PCR) primers have been designed to detect this species; however, a comparative assessment of their accuracy has not been conducted. This study aims to identify the optimal diagnostic PCR primers for the identification of A. flavus, among widely available primers. We isolated 122 A. flavus native isolates from randomly collected rice strips (N = 300). We identified 109 isolates to the genus level using universal fungal PCR primer pairs. Nine pairs of primers were examined for their PCR diagnostic specificity on the 109 isolates. FLA PCR was found to be the optimal PCR primer pair for specific identification of the native isolates, over aflP(1), aflM, aflA, aflD, aflP(3), aflP(2), and aflR. The PEP primer pair was found to be the most unsuitable for A. flavus identification. In conclusion, the present study indicates the powerful specificity of the FLA PCR primer over other commonly available diagnostic primers for accurate, rapid, and large-scale identification of A. flavus native isolates. This study provides the first simple, practical comparative guide to PCR-based screening of A. flavus infection in rice strips.

Mycoflora isolation and molecular characterization of Aspergillus and Fusarium species in Tunisian cereals

Wheat, barley and maize are the mainly consumed cereals in Tunisia. This study aimed to determine the mycoflora of these cereals with special focus on the mycotoxigenic Aspergillus and Fusarium species. Freshly harvested samples and other stored samples of each type of cereal (31 and 34 samples, respectively) were collected in Tunisia and cultured for fungal isolation and identification. Identification of fungal genera was based on morphological features. Aspergillus and Fusarium species were identified by species specific PCR assays complemented with DNA sequencing. Alternaria (70.83%), Eurotium (62.50%), Aspergillus (54.17%) and Penicillium (41.67%) were the most frequent fungi isolated from wheat. Penicillium (75%), Aspergillus (70%), Eurotium (65%) and Alternaria (65%) were the most frequently recovered genera from barley. The predominant genera in maize were Aspergillus (76.19%), Eurotium (42.86%), and Penicillium (38.09%). Aspergilllus, Penicillium, Fusarium and Alternaria were detected in both stored and freshly harvested grain samples. The frequencies of contamination with Aspergillus, Fusarium and Alternaria were higher in freshly harvested samples, whereas Penicillium species were more frequent in stored samples. The predominant Aspergillus species detected were A. flavus and A. niger. The Fusarium species detected were F. equiseti, F. verticillioides, F. nygamai, and F. oxysporum. This study suggested the potential risk for Aflatoxins and, to a lesser extent, for Ochratoxin A in Tunisian cereals. This is the first survey about mycoflora associated with wheat, barley and maize in Tunisia.

Rapid Detection and Identification of Mycotoxigenic Fungi and Mycotoxins in Stored Wheat Grain

This study aimed to assess the occurrence of toxigenic fungi and mycotoxin contamination in stored wheat grains by using advanced molecular and analytical techniques. A multiplex polymerase chain reaction (PCR) strategy was established for rapid identification of mycotoxigenic fungi, and an improved analytical method was developed for simultaneous multi-mycotoxin determination in wheat grains by liquid chromatography-tandem mass spectrometry (LC/MS/MS) without the need for any clean-up. The optimized multiplex PCR method was highly specific in detecting fungal species containing species-specific and mycotoxin metabolic pathway genes. The method was applied for evaluation of 34 wheat grain samples collected from storage warehouses for the presence of mycotoxin-producing fungi, and a few samples were found positive for Fusarium and Aspergillus species. Further chemical analysis revealed that 17 samples contained mycotoxins above the level of detection, but only six samples were found to be contaminated over the EU regulatory limits with at least one mycotoxin. Aflatoxin B₁, fumonisins, and deoxynivalenol were the most common toxins found in these samples. The results showed a strong correlation between the presence of mycotoxin biosynthesis genes as analyzed by multiplex PCR and mycotoxin detection by LC/MS/MS. The present findings indicate that a combined approach might provide rapid, accurate, and sensitive detection of mycotoxigenic species and mycotoxins in wheat grains.

Assessment of azole fungicides as a tool to control growth of Aspergillus flavus and aflatoxin B1 and B2 production in maize

Aspergillus flavus is a highly aflatoxin (AF)-producing species infecting maize and other crops. It is dominant in tropical regions, but it is also considered an emerging problem associated with climate change in Europe. The aim of this study was to assess the efficacy of azole fungicides (prochloraz, tebuconazole and a 2:1 (w/w) mixture of prochloraz plus tebuconazole) to control the growth of A. flavus and AF production in yeast-extract-sucrose (YES) agar and in maize kernels under different water activities (a_w) and temperatures. Aflatoxins B₁ and B₂ were determined by LC with fluorescence detection and post-column derivatisation of AFB₁. In YES medium and maize grains inoculated with conidia of A. flavus, the growth rate (GR) of the fungus and AFB₁ and AFB₂ production were significantly influenced by temperature and treatment. In YES medium and maize kernels, optimal temperatures for GR and AF production were 37 and 25°C, respectively. In maize kernels, spore germination was not detected at the combination 37ºC/0.95 a_w; however, under these conditions germination was found in YES medium. All fungicides were more effective at 0.99 than 0.95 a_w, and at 37 than 25ºC. Fungicides effectiveness was prochloraz > prochloraz plus tebuconazole (2:1) > tebuconazole. AFs were not detected in cultures containing the highest fungicide doses, and only very low AF levels were found in cultures containing 0.1 mg l^-1 prochloraz or 5.0 mg l^-1 tebuconazole. Azoles proved to be highly efficient in reducing A. flavus growth and AF production, although stimulation of AF production was found under particular conditions and low-dosage treatments. Maize kernels were a more favourable substrate for AF biosynthesis than YES medium. This paper is the first comparative study on the effects of different azole formulations against A. flavus and AF production in a semi-synthetic medium and in maize grain under different environmental conditions.

Impact of bioactive packaging systems based on EVOH films and essential oils in the control of aflatoxigenic fungi and aflatoxin production in maize

Aspergillus flavus and A. parasiticus are the most common fungal species associated with aflatoxin (AF) contamination of cereals, especially maize, and other agricultural commodities. AFB_1, the most frequent and toxic metabolite, is a powerful hepatotoxic, teratogenic and mutagenic compound. Effective strategies to control these fungal species and AFs in food and feed are required. Active packaging film containing essential oils (EO) is one of the most innovative food packaging concepts. In this study, ethylene-vinyl alcohol (EVOH) copolymer films incorporating EO from Origanum vulgare (ORE), Cinnamomum zeylanicum (CIN) or their major active constituents, carvacrol (CAR) and cinnamaldehyde (CINHO), respectively, were developed and assayed to control growth of A. flavus and A. parasiticus and AF production in maize grains under different a_w and temperature regimens. EO doses assayed in cultures were in the range 0.25-4.0mg/Petri dish. The factors a_w, temperature, type of EVOH-EO film and fungal species significantly influenced the ED₅₀ values of all assayed films. Growth rate (GR) of both species was usually higher at 0.99 than at 0.96 a_w and at 37°C than at 25°C. However, the contrary was found with regard to AF production. The order of efficacy of EVOH-EO films to control growth of both species and AF production was EVOH-CINHO>EVOH-CAR>EVOH-ORE>EVOH-CIN. The effective dose (ED₅₀) (mg EO/plate) for EVOH-CINHO and EVOH-CIN films against A. flavus were in the ranges of 0.125 and 2.475-3.500 and against A. parasiticus in the ranges of 0.121-0.133 and 2.275-3.625, respectively. Under the assayed conditions, the ED₉₀ for EVOH-CINHO film were 0.22-0.23mg/plate for both species. It was the most effective bioactive film to control fungal growth (vapour phase) and AF production, regardless of a_w and temperature. This is the first study about the impact that interacting environmental conditions and bioactive EVOH-CINHO, EVOH-ORE, EVOH-CIN EVOH-CAR films have on the growth of aflatoxigenic fungi and on AF production in maize grains.

Aflatoxins and ochratoxin A and their Aspergillus causal species in Tunisian cereals

Occurrence of aflatoxins (AFs) AFB1, AFB2, AFG1, AFG2 and ochra toxin A (OTA) was studied in 65 samples of stored and freshly harvested wheat, barley and maize collected in Tunisia. The mycotoxins were simultaneously extracted and quantified by high performance liquid chromatography. Determination of AF-producing (section Flavi) and OTA-producing Aspergillus species (sections Nigri and Circumdati) was conducted in these samples by species-specific polymerase chain reaction (PCR). Results showed that most of maize samples were contaminated with AFs, data after storage showing lower values than those collected at harvest. All contaminated maize samples contained AFG1 and AFG2, among which 27.78% also had AFB1 and AFB2. This AFs pattern was consistent with the A. parasiticus toxin profile. A. flavus however showed the highest frequency in maize but was also found in barley and wheat where no AFs were detected. In contrast, OTA was neither found in maize nor in barley and only one wheat sample contained OTA. A. niger was the only OTA-producing species detected.

Fungal diversity, incidence and mycotoxin contamination in grapes from two agro-climatic Spanish regions with emphasis on Aspergillus species

BACKGROUND

Fourteen vineyards from two different agro-climatic regions in Spain were sampled in two consecutive years in order to determinate the grape mycobiota and diversity indexes with the final aim to define the potential mycotoxigenic species from both regions and their relationship.

RESULTS

The most common fungal genera encountered were Aspergillus (30.0%), Alternaria (53.2%), Cladosporium (11.9%) and Penicillium (2.9%). Black aspergilli presence in the hotter region (south) was significantly higher (P < 0.05) than in the northeast in both years. Among black aspergilli, A. tubingensis seemed to be the better adapted species to environmental conditions, while A. carbonarius was the main potentially ochratoxigenic species in both regions and years, owing to the most relevant percentage of ochratoxigenic isolates. Ochratoxin A (OTA)-positive musts were only detected from southern vineyards, although contamination was always lower than 0.1 µg L(-1) . Finally, none of black aspergilli tested produced fumonisins (FBs) on Czapek yeast extract agar (CYA), while 63% of A. niger tested produced FB2 when inoculated on CYA20S, reaching 100% of isolates from the south.

CONCLUSION

Climate change scenarios in southern Europe point to an increase in temperature and drought. This could promote particularly adapted species such as A. niger, decreasing OTA risk, but this could lead to an increase in FB2 presence.

Detection of Aspergillus flavus in stored peanuts using real-time PCR and the expression of aflatoxin genes in toxigenic and atoxigenic A. flavus isolates

Aspergillus flavus is the main species from section Flavi responsible for aflatoxin accumulation in stored peanuts. Rapid methods to detect A. flavus could help to prevent aflatoxins from entering the food chain. A real-time polymerase chain reaction (RTi-PCR) assay was standardized for rapid, specific, and sensitive detection of A. flavus in stored peanuts. A. flavus was detected in 53.6% and 50% of peanut samples by RTi-PCR and A. flavus and Aspergillus parasiticus agar culture, respectively, with 95% agreement between them. Twenty-two A. flavus isolates were screened using high-performance liquid chromatography for their capacity to produce aflatoxin AFB1 (B1). B1 was produced by >72% of the isolates. Sixteen isolates produced B1 at concentrations ranging from 1.64 to 109.18 μg/mL. Four aflatoxin biosynthetic pathway genes (aflD, aflM, aflP, and aflQ) were evaluated using PCR and reverse-transcription PCR in 22 A. flavus isolates from peanut kernels with the aim of rapidly and accurately differentiating toxigenic and atoxigenic isolates. The PCR amplification of genes did not correlate with aflatoxin production capability. The expression of aflD and aflQ was a good marker for differentiating toxigenic from atoxigenic isolates.

Development and evaluation of ITS- and aflP-based LAMP assays for rapid detection of Aspergillus flavus in food samples

Aspergillus flavus is a common filamentous fungus that produces aflatoxins and presents a major threat to agriculture and human health. Previous studies focused mainly on the detection of A. flavus or aflatoxin separately. Here, we developed internal transcribed spacer (ITS)- and aflP-based rapid detection of A. flavus in food samples using the loop-mediated isothermal amplification (LAMP) method. The ITS1-5.8S-ITS2 rDNA region of A. flavus and the aflatoxin-encoding gene aflP were used as target regions. The detection limits of A. flavus and aflP were 10 fg and 1 pg pure DNA, respectively, which allows aflatoxin-contaminated samples to be differentiated from infected samples and reduces false-negative or false-positive results. For specificity testing, DNA extracted from 7 A. flavus, 5 different Aspergillus spp., and 21 other fungi were used, and our results showed that A. flavus strains are detected by ITS-based detection and aflatoxigenic A. flavus strains are detected by aflP-based detection. Furthermore, the ITS- and aflP-based LAMP assays were used for detection analysis of DNA from food samples artificially and naturally contaminated with A. flavus. Our results showed that the detection rate of A. flavus based on the multi-ITS-based LAMP detection is 100% and that the aflatoxigenic strains in all A. flavus are detected by the aflP-based LAMP assay. The LAMP protocol described in our study represents a rapid and highly specific and sensitive diagnostic method for A. flavus detection, which can be used as a diagnostic tool that simplifies A. flavus monitoring and guarantees the quality and safety of foods.

In vitro effect of some fungicides on growth and aflatoxins production by Aspergillus flavus isolated from Capsicum powder

The aim of this study was to determine the effect of some pre-harvest fungicides on growth and aflatoxin (AF) production of three Aspergillus flavus strains found in Capsicum powder. Each isolate, previously isolated from paprika, chilli and smoked paprika, was inoculated on yeast extract sucrose agar and on a 3% paprika extract agar medium supplemented with different fungicides and incubated at 20 and 30°C during 7 days. Growth measurements were obtained on days 3, 5 and 7, and the AF production was determined on day 7. The significance of the effects of the factors (strain, medium, temperature, time and fungicides) and their interaction over colony diameter and AF production was determined. Temperature constrained the effectiveness of fungicides in reducing growth, the fungicides being most effective at 20°C. The efficacy of the fungicides over AF production depended on the medium used and temperature. The most effective fungicides in inhibiting growth and AF production, regardless of the strain tested or applied conditions, were tebuconazole 25% and mancozeb 80% applied at a concentration of 0.75 and 3.5 g l(-1), respectively. Care should thus be taken in the choice of a suitable fungicide because their effectiveness may depend on intra-specific variation and temperature. Moreover, it is necessary to take into account that the most efficient fungicide in reducing growth is not always the best choice for pre-harvest treatments because it may promote AF production. Thus, the best fungicide is the one that can simultaneous prevent growth and AF production.

Comparison of soil fungal community structure in different peanut rotation sequences using ribosomal intergenic spacer analysis in relation to aflatoxin-producing fungi

The present study focuses on determining soil fungal community structure in different peanut-cropping sequences by using a high-resolution DNA fingerprinting technique: ribosomal intergenic spacer analysis (RISA). This study was initiated to determine fungal community profiles in four peanut-cropping sequences (continuous peanut, 4 years of continuous bahiagrass followed by peanut, peanut-corn-cotton, and peanut-cotton rotations), with a special focus to evaluate whether the profiles under investigation may have also indicated microbial differences that could affect Aspergillus flavus populations. Results indicated 75% similarities among fungal communities from the same cropping sequences as well as with similar times of sampling. Polymerase chain reaction (PCR)-based detection of A. flavus directly from these soils was carried out using A. flavus-specific primers (FLA1 and FLA2) and also through quantitative estimation on A. flavus and A. parasiticus agar medium. Population levels of A. flavus in soil samples ranged from zero to 1.2 × 10(3) CFU g(-1) of soil (based on culturable methods); however, the fungus was not detected with A. flavus-specific primers. The minimum threshold limit at which these aflatoxin-producing fungi could be detected from the total soil genomic DNA was determined through artificial inoculation of samples with 10-fold increases in concentrations. The results indicated that a minimum population density of 2.6 × 10(6) CFU g(-1) of soil is required for PCR detection in our conditions. These results are useful in further determining the relative population levels of these fungi in peanut soils with other soil fungi. This is a new approach to understanding soil fungal communities and how they might change over time and under different rotation systems.

Highly sensitive PCR-based detection specific to Aspergillus flavus

Aspergillus flavus is an important fungal species that frequently contaminates food commodities with diverse toxins, with aflatoxins being the most relevant in food safety. In addition, this is one of the major pathogenic Aspergillus species. In this work, specific PCR-based protocol for this species is described which allows the discrimination of other closely related species from the Aspergillus section Flavi, particularly Aspergillus parasiticus. The specific primers were designed on the multicopy internal transcribed region of the rDNA unit (ITS1-5.8S-ITS2 rDNA).

Mycotoxigenic fungi in peanuts from different geographic regions of Egypt

To understand the importance of mycotoxigenic fungi in Egyptian peanuts, samples from five regions (Alexandria, El-Beheira, El-Sharqiya, El-Daqahelaya in northern Egypt and Asyut, southern Egypt) in two seasons (2007, 2008) were collected. Aspergillus was consistently the most frequent genus in seeds and in-shell peanuts and was the dominant mycotoxigenic component of the mycobiota. There was no direct correlation between the moisture content of the samples and the fungal populations on peanut seeds tested from different regions. The most common species were from Aspergillus section Flavi (4.7-78.3%), Aspergillus section Nigri (9.4-52.6%) and Aspergillus section Circumdati (5.1-30.9%). In the in-shell peanut samples, the lowest populations were recorded in El-Beheira and Asyut (3.7-4.0 log10 CFU g(-1)) and the highest in Alexandria and Elsharqiya (4.1-6.0 log10 CFU g(-1)). Aspergillus section Flavi and section Nigri were the most dominant, and Aspergillus section Circumdati were only found in samples in 2008. Both qualitative (coconut cream agar) and quantitative analyses (HPLC) were used to analyse the potential mycotoxin production by strains isolated from peanuts. Of a total of 88 Aspergillus section Flavi strains examined, 95% were A. flavus based on production of aflatoxin B1 on yeast extract sucrose (YES) medium and confirmation using molecular analyses. Of 64 Aspergillus section Circumdati strains only 28% produced ochratoxin A (OTA), and were identified as A. westerdijkiae. No Aspergillus section Nigri strains produced OTA, and they were identified as A. niger (uniseriate). The presence of these toxigenic fungi indicates that there is a potential risk of mycotoxin contamination in Egyptian peanuts and suggests that problems can arise from contamination with both aflatoxins and perhaps also OTA.