Isolation and identification of ochratoxin A-producing Aspergillus section Nigri strains from California raisins

Unlocking the Transcriptional Reprogramming Repertoire between Variety-Dependent Responses of Grapevine Berries to Infection by Aspergillus carbonarius

Aspergillus carbonarius causes severe decays on berries in vineyards and is among the main fungal species responsible for grape contamination by ochratoxin A (OTA), which is the foremost mycotoxin produced by this fungus. The main goal of this study was to investigate at the transcriptome level the comparative profiles between two table grape varieties (Victoria and Fraoula, the white and red variety, respectively) after their inoculation with a virulent OTA-producing A. carbonarius strain. The two varieties revealed quite different transcriptomic signatures and the expression profiles of the differential expressed genes (DEGs) highlighted distinct and variety-specific responses during the infection period. The significant enrichment of pathways related to the modulation of transcriptional dynamics towards the activation of defence responses, the triggering of the metabolic shunt for the biosynthesis of secondary metabolites, mainly phenylpropanoids, and the upregulation of DEGs encoding phytoalexins, transcription factors, and genes involved in plant-pathogen interaction and immune signaling transduction was revealed in an early time point in Fraoula, whereas, in Victoria, any transcriptional reprogramming was observed after a delay. However, both varieties, to some extent, also showed common expression dynamics for specific DEG families, such as those encoding for laccases and stilbene synthases. Jasmonate (JA) may play a critical modulator role in the defence machinery as various JA-biosynthetic DEGs were upregulated. Along with the broader modulation of the transcriptome that was observed in white grape, expression profiles of specific A. carbonarius genes related to pathogenesis, fungal sporulation, and conidiation highlight the higher susceptibility of Victoria. Furthermore, the A. carbonarius transcriptional patterns directly associated with the regulation of the pathogen OTA-biosynthesis gene cluster were more highly induced in Victoria than in Fraoula. The latter was less contaminated by OTA and showed substantially lower sporulation. These findings contribute to uncovering the interplay beyond this plant-microbe interaction.

Comprehensive Review of Aflatoxin and Ochratoxin A Dynamics: Emergence, Toxicological Impact, and Advanced Control Strategies

Filamentous fungi exhibit remarkable adaptability to diverse substrates and can synthesize a plethora of secondary metabolites. These metabolites, produced in response to environmental stimuli, not only confer selective advantages but also encompass potentially deleterious mycotoxins. Mycotoxins, exemplified by those originating from Alternaria, Aspergillus, Penicillium, and Fusarium species, represent challenging hazards to both human and animal health, thus warranting stringent regulatory control. Despite regulatory frameworks, mycotoxin contamination remains a pressing global challenge, particularly within cereal-based matrices and their derived by-products, integral components of animal diets. Strategies aimed at mitigating mycotoxin contamination encompass multifaceted approaches, including biological control modalities, detoxification procedures, and innovative interventions like essential oils. However, hurdles persist, underscoring the imperative for innovative interventions. This review elucidated the prevalence, health ramifications, regulatory paradigms, and evolving preventive strategies about two prominent mycotoxins, aflatoxins and ochratoxin A. Furthermore, it explored the emergence of new fungal species, and biocontrol methods using lactic acid bacteria and essential mustard oil, emphasizing their efficacy in mitigating fungal spoilage and mycotoxin production. Through an integrative examination of these facets, this review endeavored to furnish a comprehensive understanding of the multifaceted challenges posed by mycotoxin contamination and the emergent strategies poised to ameliorate its impact on food and feed safety.

Ochratoxin A Contamination of California Pistachios and Identification of Causal Agents

Ochratoxin A (OTA) is a potent mycotoxin produced by Aspergillus and Penicillium spp., which contaminates many crops, including pistachios. Pistachios contaminated with OTA may be subjected to border rejections resulting in significant economic losses to the United States agricultural revenues. The current study examined prevalence of OTA in California-grown pistachios and identified its causal agents. OTA was detected in 20% of samples from 2018 to 2021 (n = 809), with 18% of samples exceeding the European Union regulatory limit of 5 μg/kg. Fungi potentially responsible for OTA contamination were isolated from leaves, nuts, and soil collected from 14 pistachio orchards across California. A total of 1,882 isolates of Aspergillus section Nigri and 85 isolates of section Circumdati were recovered. Within section Nigri, 216 (11.5%) isolates were identified as potential OTA producers using a boscalid-resistance assay. Phylogenetic analyses of partial gene sequences for β-tubulin and calmodulin genes resolved section Circumdati into four species: A. ochraceus (33%), A. melleus (28%), A. bridgeri (21%), and A. westerdijkiae (19%). A. westerdijkiae produced the highest levels of OTA in inoculated pistachios (47 μg/g), followed by A. ochraceus (9.6 μg/g) and A. melleus (3.3 μg/g). A. bridgeri did not produce OTA. OTA production by section Circumdati was optimal from 20 to 30°C. All 216 boscalid-resistant isolates from section Nigri were identified as A. tubingensis, and representative isolates (n = 130) produced 3.8 μg/kg OTA in inoculated pistachios. This is the first detailed report on OTA contamination and causal fungi in California pistachios and will be helpful in devising effective management strategies.

Comprehensive Insights into Ochratoxin A: Occurrence, Analysis, and Control Strategies

Ochratoxin A (OTA) is a toxic mycotoxin produced by some mold species from genera Penicillium and Aspergillus. OTA has been detected in cereals, cereal-derived products, dried fruits, wine, grape juice, beer, tea, coffee, cocoa, nuts, spices, licorice, processed meat, cheese, and other foods. OTA can induce a wide range of health effects attributable to its toxicological properties, including teratogenicity, immunotoxicity, carcinogenicity, genotoxicity, neurotoxicity, and hepatotoxicity. OTA is not only toxic to humans but also harmful to livestock like cows, goats, and poultry. This is why the European Union and various countries regulate the maximum permitted levels of OTA in foods. This review intends to summarize all the main aspects concerning OTA, starting from the chemical structure and fungi that produce it, its presence in food, its toxicity, and methods of analysis, as well as control strategies, including both fungal development and methods of inactivation of the molecule. Finally, the review provides some ideas for future approaches aimed at reducing the OTA levels in foods.

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.

The Occurrence and Contamination Level of Ochratoxin A in Plant and Animal-Derived Food Commodities

Ochratoxin A (OTA) is a highly toxic mycotoxin and poses great threat to human health. Due to its serious toxicity and widespread contamination, great efforts have been made to evaluate its human exposure. This review focuses on the OTA occurrence and contamination level in nine plant and animal derived food commodities: cereal, wine, coffee, beer, cocoa, dried fruit, spice, meat, and milk. The occurrence and contamination level varied greatly in food commodities and were affected by many factors, including spices, geography, climate, and storage conditions. Therefore, risk monitoring must be routinely implemented to ensure minimal OTA intake and food safety.

Antifungal activity of Saccharomyces cerevisiae and assessment of ochratoxigenic load on currants by means of Real Time PCR

Currants are prone to contamination by ochratoxin during cultivation, processing and storage conditions. Saccharomyces cerevisiae is considered to be among the main species of grape yeast flora able to control antagonistic fungi. In this study, the potential of S. cerevisiae Y₃₃ was investigated to inhibit the growth of several fungal species indigenous to the microbiota of grapes. Moreover, the efficacy of this yeast species was investigated to inhibit OTA by toxin producing fungi both in vitro and in situ. For this purpose thirty-five different fungal species, belonging to the genera Aspergillus, Penicillium, Cladosporium, Fusarium and Alternaria interacted in vitro with S. cerevisiae on Malt Extract agar plates, stored at 25 °C for 14 days. Results showed that the highest OTA producer A. carbonarius F₇₁ was inhibited more than 99% from day 7, in contrast to A. niger strains that presented enhanced OTA production at day 14 due to interaction with S. cerevisiae Y₃₃. Additionally, the antifungal potential of the selected yeast was also studied in situ on currants subjected to different treatments and stored at 25 °C for 28 days. Microbiological analysis was undertaken for the enumeration of the bacterial and fungal flora, together with OTA determination at 7 and 21 days. To quantify A. carbonarius on all treated currant samples, molecular analysis with Real Time PCR was employed. A standard curve was prepared with A. carbonarius DNA. The efficiency of the curve was estimated to 10.416, the slope to -3.312 and the range of haploid genome that could be estimated was from 1.05 to 105∙10⁵. The amount of A. carbonarius DNA in all treated currants samples, where the fungus was positively detected, ranged from as low as 0.08 to 562 ng DNA/g currants. The antifungal activity of S. cerevisiae Y₃₃ was observed in all studied cases, causing inhibition of fungal growth and OTA production.

Genetic Diversity, Ochratoxin A and Fumonisin Profiles of Strains of Aspergillus Section Nigri Isolated from Dried Vine Fruits

We investigated ochratoxin A (OTA) contamination in raisin samples purchased from Slovak markets and determined the diversity of black-spored aspergilli as potential OTA and fumonisin (FB1 and FB2) producers. The taxonomic identification was performed using sequences of the nuclear ITS1-5.8s-ITS2 region, the calmodulin and beta-tubulin genes. We obtained 239 isolates from eight fungal genera, of which 197 belonged to Aspergillus (82%) and 42 strains (18%) to other fungal genera. OTA contamination was evidenced in 75% of the samples and its level ranged from 0.8 to 10.6 µg/kg. The combination of all three markers used enabled unambiguous identification of A. carbonarius, A. luchuensis, A. niger, A. tubingensis and A. welwitschiae. The dominant coloniser, simultaneously having the highest within-species diversity isolated from our raisin samples, was A. tubingensis. Out of all analysed strains, only A. carbonarius was found to produce OTA, but in relatively high quantity (2477–4382 µg/kg). The production of FB1 and FB2 was evidenced in A. niger strains only.

Pest Management and Ochratoxin A Contamination in Grapes: A Review

Ochratoxin A (OTA) is the most toxic member of ochratoxins, a group of toxic secondary metabolites produced by fungi. The most relevant species involved in OTA production in grapes is Aspergillus carbonarius. Berry infection by A. carbonarius is enhanced by damage to the skin caused by abiotic and biotic factors. Insect pests play a major role in European vineyards, and Lepidopteran species such as the European grapevine moth Lobesia botrana are undoubtedly crucial. New scenarios are also emerging due to the introduction and spread of allochthonous pests as well as climate change. Such pests may be involved in the dissemination of OTA producing fungi even if confirmation is still lacking and further studies are needed. An OTA predicting model is available, but it should be integrated with models aimed at forecasting L. botrana phenology and demography in order to improve model reliability.

Diversity and ochratoxin A-fumonisin profile of black Aspergilli isolated from grapes in China

Aspergillus spp. are a common contaminant of grapes and a major source of mycotoxins. China is the largest producer of grape in the world now, however, the toxigenic Aspergillus population on grape in this country is still largely unknown. In this study, a total of 345 strains were isolated from grapes of 13 main grapevine producing regions in China. Based on calmodulin gene sequences, eight species within Aspergillus section Nigri were identified. Among them, Aspergillus tubingensis (48.7%) was predominant, followed by Aspergillus welwitschiae (20.6%) and Aspergillus aculeatinus (11%). Average of contamination level was up to 64.19%, and we found the occurrence of section Nigri species on the surface of fresh grapes was significantly influenced by the climate (P<0.05). The subtropical monsoon climate showed the highest fungal detection rate (72.45%), followed by the temperate monsoon climate (49.82%), and the lowest frequency was found in the temperate continental climate (37.23%). Regarding mycotoxin-producing capacity, 4.4% of the total tested section Nigri isolates (137) were positive for ochratoxin A (OTA) production and 59.6% were fumonisin B2 (FB2) producers. Of those, Aspergillus carbonarius was the main OTA producer and A. welwitschiae and Aspergillus niger were the main FB2 producers with different toxigenic ability. Our results highlight the potential risk of OTA and FB2 contamination by A. carbonarius and A. welwitschiae on grape in China, respectively; management strategies should be considered for preventing and reducing the toxigenic Aspergillus and its mycotoxins.

Interacting climate change factors (CO2 and temperature cycles) effects on growth, secondary metabolite gene expression and phenotypic ochratoxin A production by Aspergillus carbonarius strains on a grape-based matrix

Little is known on the impact that climate change (CC) may have on Aspergillus carbonarius and Ochratoxin A (OTA) contamination of grapes, especially in the Mediterranean region where in CC scenarios temperature are expected to increase by +2-5 °C and CO₂ from 400 to 800/1200 ppm. This study examined the effect of (i) current and increased temperature in the alternating 11.5 h dark/12.5 h light cycle (15-28 °C vs 18-34 °C), representative of the North Apulia area, South Italy and (ii) existing and predicted CO₂ concentrations (400 vs 1000 ppm), on growth, expression of biosynthetic genes (AcOTApks, AcOTAnrps, AcOTAhal, AcOTAp450, AcOTAbZIP) and regulatory genes of Velvet complex (laeA/veA/velB, "velvet complex") involved in OTA biosynthesis and OTA phenotypic production by three strains of A. carbonarius. The experiments made on a grape-based matrix showed that elevated CO₂ resulted in a general stimulation of growth and OTA production. These results were also supported by the up-regulation of both structural and regulatory genes involved in the OTA biosynthesis. Our work has shown for the first time that elevated CO₂ concentration in the Mediterranean region may result in an increased risk of OTA contamination in the wine production chain.

Effect of potassium sorbate (E-202) and the antifungal PgAFP protein on Aspergillus carbonarius growth and ochratoxin A production in raisin simulating media

BACKGROUND

Ochratoxin A (OTA) is a mycotoxin produced by several species of Aspergillus and Penicillium fungi. The presence of OTA in raisins is mainly related to black Aspergillus spp. contamination. This toxin poses risks to human and animal health due to its high toxicity and carcinogenicity. New strategies to avoid the risk associated with OTA are therefore necessary.

RESULTS

A comparison was made between the effects of the antifungal protein PgAFP and potassium sorbate (E-202) on the growth of Aspergillus carbonarius, biosynthetic- and stress-related gene expression and its OTA production at two water activity (a_w ) levels, 0.95 and 0.93 a_w . The results showed that PgAFP successfully controlled OTA production, whereas E-202, despite being able to reduce Aspergillus carbonarius growth, caused a significant increase in OTA production by the fungus.

CONCLUSION

PgAFP protein, a biological compound with an antifungal activity, is safer to use than E-202 and may be proposed as a food preservative and a useful strategy to control ochratoxigenic A. carbonarius in raisins. © 2018 Society of Chemical Industry.

Raisins and Currants as Conventional Nutraceuticals in Italian Market: Natural Occurrence of Ochratoxin A

The healthy consumers make a strong pressure to natural products that can prevent the chronic diseases and improve the general health status, and therefore an important aspect that have to be considered is the safe level of the nutraceuticals. This study reports the occurrence of Ochratoxin A (OTA) and associated fungal contamination in 35 samples of dried vine fruits imported in the European community potentially used for the development of new nutraceutical supplements. High pressure liquid chromatography analysis identified 18 samples as contaminated by OTA with an average level of 2.6 μg/kg. OTA was measured in 4 samples of currants (mean value of 6.6 μg/kg) and 13 samples of raisins (mean value of 1.4 μg/kg). In one sample of currants and one of raisins from Turkey OTA exceeded the limits set by European Commission of 10 μg/kg, being contaminated with 12.61 and 15.99 μg/kg, respectively. All the positive samples were confirmed by Orbitrap Q Exactive through their molecular weight and the corresponding fragmentation. The worldwide consumption of dried vine fruits contributed to OTA exposure in several group of consumers. In particular, considering the potential nutraceutical approach, this consumption may be represent a severe risk for healthy consumers that consider these products like healthy and salutistic for their contents in antioxidants, flavonoids, and polyphenols. Data reported in this study confirmed the need to regularly monitor mycotoxin levels in these food products and optimize the process of fruits drying in order to reduce the development of toxigenic molds.

Differentiation and identification of grape-associated black aspergilli using Fourier transform infrared (FT-IR) spectroscopic analysis of mycelia

The purpose of this study was to evaluate the potential of FT-IR spectroscopy as a high-throughput method for rapid differentiation among the ochratoxigenic species of Aspergillus carbonarius and the non-ochratoxigenic or low toxigenic species of Aspergillus niger aggregate, namely A. tubingensis and A. niger isolated previously from grapes of Greek vineyards. A total of 182 isolates of A. carbonarius, A. tubingensis, and A. niger were analyzed using FT-IR spectroscopy. The first derivative of specific spectral regions (3002-2801cm^-1, 1773-1550cm^-1, and 1286-952cm^-1) were chosen and evaluated with respect to absorbance values. The average spectra of 130 fungal isolates were used for model calibration based on Discriminant analysis and the remaining 52 spectra were used for external model validation. This methodology was able to differentiate correctly 98.8% in total accuracy in both model calibration and validation. The per class accuracy for A. carbonarius was 95.3% and 100% for model calibration and validation, respectively, whereas for A. niger aggregate the per class accuracy amounted to 100% in both cases. The obtained results indicated that FT-IR could become a promising, fast, reliable and low-cost tool for the discrimination and differentiation of closely related fungal species.

Aspergillus labruscus sp. nov., a new species of Aspergillus section Nigri discovered in Brazil

A novel fungal species, Aspergillus labruscus sp. nov., has been found in Brazil during an investigation of the fungal species present on the surface of grape berries (Vitis labrusca L.) for use in the production of concentrated grape juice. It seems to be associated to V. labrusca, and has never been recovered from Vitis vinifera. This new species belonging to Aspergillus subgenus Circumdati section Nigri is described here using morphological characters, extrolite profiling, partial sequence data from the BenA and CaM genes, and internal transcribed spacer sequences of ribosomal DNA. Phenotypic and molecular data enabled this novel species to be clearly distinguished from other black aspergilli. A. labruscus sp. nov. is uniseriate, has yellow mycelium, poor sporulation on CYA at 25 °C, abundant salmon to pink sclerotia and rough conidia. Neoxaline and secalonic acid D were consistently produced by isolates in this taxon. The type strain of A. labruscus sp. nov. is CCT 7800 (T) = ITAL 22.223 (T) = IBT 33586 (T).

Population Dynamics of Aspergillus Section Nigri Species on Vineyard Samples of Grapes and Raisins

Several species of Aspergillus section Nigri, including potential mycotoxin producers, are common residents of grape vineyards, but the relative population size of individual species throughout the growing season is difficult to determine using traditional isolation and identification methods. Using a quantitative droplet digital PCR (ddPCR) method in combination with dilution plating, total Aspergillus section Nigri populations and relative proportions of A. niger, A. welwitschiae, A. carbonarius, and A. tubingensis were measured from vineyard samples without the need for identifying individual fungal isolates. Grapes were sampled from two raisin vineyards (vineyards A and B) at berry set, veraison, harvest, and raisin stages in two consecutive years. Plate counts showed that the total population of Aspergillus section Nigri present on the fruit increased from berry set to raisin and became a larger component of the total recovered fungal population in both vineyards in both years. Results from ddPCR analysis showed that the relative proportion of A. carbonarius among the four species assayed increased later in the season (harvest and raisin) in comparison to earlier in the season (berry set and veraison). Total fungal and Aspergillus section Nigri plate counts were not significantly different between vineyards in either year. However, vineyard A generally showed higher proportions of A. carbonarius in harvest and raisin samples than vineyard B. This coincided with higher incidence and levels of ochratoxin A in vineyard A harvest and raisin fruit than in vineyard B fruit. This work demonstrates that this ddPCR method is a useful tool for culture-independent monitoring of populations of mycotoxigenic Aspergillus species during grape and raisin production.

Diversity of Mycotoxin-Producing Black Aspergilli in Canadian Vineyards

Several Aspergillus species produce ochratoxin A (OTA) and/or fumonisins on wine and table grapes. The relevant species and their mycotoxins have been investigated in a number of wine-producing regions around the world; however, similar data have not been reported for Canadian vineyards. A multiyear survey of black Aspergilli in Niagara, ON, vineyards was conducted to determine the diversity of species present and to assess the risk of OTA and fumonisin contamination of wine grapes from this region. From 2012 to 2014, 253 black Aspergilli were isolated from soil samples and the fruits of 10 varieties of grapes. The isolates were identified by DNA sequencing: Aspergillus welwitschiae (43%), Aspergillus uvarum (32%), Aspergillus brasiliensis (11%), Aspergillus tubingensis (9%), and Aspergillus niger (4%). Aspergillus carbonarius, the primary OTA producer on grapes in other parts of the world, was isolated only once, and this is the first report for it in Canada. All 10 A. niger strains produced fumonisins, but, in contrast, only 26% of the 109 A. welwitschiae isolates were producers, and no strains of either species produced OTA. Grape samples were analyzed for OTA and fumonisins from sites where strains with mycotoxigenic potential were isolated. Fumonisin B2 (FB2) was detected in 7 of 22 (32%) of these grape samples in the 1-15 ppb range, but no OTA was detected. Additionally, the recently reported nonaminated fumonisins were detected in 3 of 22 grape samples. These results suggest that fumonisin-producing Aspergilli can occur in Ontario vineyards but, at present, the risk of contamination of grapes appears low. The risk of OTA contamination in Niagara wine is also low because of the low prevalence of A. carbonarius.

Ochratoxin A in dried grapes in Hamadan province, Iran

The occurrence of ochratoxin A (OTA) in dried grapes was surveyed in this study. Sixty-six samples of dried grapes (40 currants, 16 sultanas and 10 raisins) were collected from dried grapes factories in Hamadan province, Iran, from October 2012 to March 2013. High-performance liquid chromatography (HPLC) was used to determine OTA in these samples. OTA was detected in 23 (57.5%) currants, 10 (62.5%) sultanas and 6 (60%) raisins samples. Levels in five samples exceeded the Institute of Standards and Industrial Research of Iran (ISIRI) maximum level of 5 µg/kg. However, OTA content in none of the samples exceeded the maximum limit prescribed in the European Union (EU) regulations, which is 10 µg/kg. The obtained data contribute to information on OTA levels in Iranian dried grapes.

Occurrence of ochratoxin a contamination and detection of ochratoxigenic Aspergillus species in retail samples of dried fruits and nuts

Ochratoxin A (OTA) is a mycotoxin produced by several species of Aspergillus and Penicillium and is a potential contaminant of a wide variety of food products. To determine the incidence of OTA contamination in dried fruits and tree nuts, retail packaged and bulk raisins, dates, figs, prunes, almonds, pistachios, and walnuts were collected from small and large supermarkets in seven areas of the United States between 2012 and 2014. Of the 665 samples analyzed, OTA was detected in 48 raisin samples, 4 fig samples, 4 pistachio samples, and 1 date sample. OTA contamination levels ranged from 0.28 to 15.34 ng/g in dried fruits and 1.87 to 890 ng/g in pistachios; two raisin samples and one pistachio sample exceeded the European Union regulatory limit of 10 ng/g. PCR detection of potential OTA-producing Aspergillus species revealed the presence of A. niger, A. welwitschiae, and A. carbonarius in 20, 7, and 7 of the 57 OTA-contaminated samples, respectively. However, OTA-producing A. carbonarius was isolated from only one raisin sample, and no other OTA-producing Aspergillus species were found. These results suggest that raisins are more frequently contaminated with low levels of OTA than are other dried fruits and nuts and that Aspergillus species are the likely source of that contamination.

Detection and discrimination of four Aspergillus section Nigri species by PCR

Species of Aspergillus section Nigri are not easily distinguished by traditional morphological techniques, and typically are identified by DNA sequencing methods. We developed four PCR primers to distinguish between Aspergillus niger, Aspergillus welwitschiae, Aspergillus carbonarius and Aspergillus tubingensis, based on species-conserved differences in the calmodulin gene sequence. PCR amplification from total DNA using these primers was species specific; no amplification occurred from nontarget species DNA for each primer pair. Species-specific PCR could distinguish between species in mixed DNA templates, indicating a utility in determining culture uniformity of isolated Aspergillus strains. In addition, with these primer sets, each species could be detected in soil following mixed-species inoculation with Aspergillus spores. This indicates that PCR with these species-specific primers may be useful in determining the distribution of Aspergillus species in environmental samples without the need for species identification from isolated strains, as well as detecting species that may be infrequently isolated by culture-based methods.

Biodiversity and ITS-RFLP characterisation of Aspergillus section Nigri isolates in grapes from four traditional grape-producing areas in Greece

A study on the occurrence of Aspergillus section Nigri species on grapes from four traditional grape-producing areas in Greece during the 2011/2012 vintage, and their capability to produce OTA was conducted. One hundred and twenty-eight black aspergilli isolates were characterised at the species level initially by the use of morphological criteria in accordance with appropriate keys, followed by molecular characterisation performed with Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) of the 5.8 ribosomal RNA gene Internal Transcribed Spacer region (5.8 rRNA ITS). Restriction enzyme digestion of the ITS amplicons using the HhaI, HinfI and RsaI, endonucleases distinguished eleven different patterns of restriction fragment length polymorphism (RFLP), four for each of the HhaI and RsaI digests and three for HinfI. From a total number of 128 individual isolates, 124 were classified into four Aspergillus species corresponding to A. carbonarius, A. tubingensis, A. japonicus and A. ibericus, and the remaining 4 were classified as members of the A. niger aggregate. A. carbonarius and A. tubingensis being the main representative species were equally counted, with higher geographical representation of the former in southern and the latter in northern regions, respectively. All isolates were tested for their ochratoxigenic potential by use of High Performance Liquid Chromatography (HPLC) and Enzyme Linked Immuno Sorbent Assay (ELISA), resulting in significant interspecies differences in OTA production.

Microbiological food safety and a low-microbial diet to protect vulnerable people

Low-microbial diets are advised by many institutions for people with neutropenia resulting from treatment with immunosuppressive drugs or medical conditions that increase their susceptibility to foodborne disease. In this article, the main microbiological hazards associated with foods are outlined, and a low-microbial diet in which higher-risk foods are replaced by lower-risk foods is described.

A validated dispersive liquid-liquid microextraction method for extraction of ochratoxin A from raisin samples

A method based on dispersive liquid-liquid microextraction (DLLME) was developed for the quantitative extraction of Ochratoxin A (OTA) from raisin samples. The influence of various parameters on the recovery of OTA such as type and volume of DLLME extractant, centrifuging and sonication time, also volume of deionized water was investigated. Recovery values under the optimum conditions were between 68.6 and 85.2 %, the inner and intra-day precision expressed as relative standard deviation (RSD%, n = 3), were less than 15 % at spiking levels of 2.5-30 μg kg(-1). Linearity was studied from 0.5 to 30 μg L(-1), and the limits of detection (LOD) and quantification (LOQ) were 0.7 and 2.0 μg kg(-1), respectively. Real samples were analyzed by DLLME method and compared with confirmative immunoaffinity Column Chromatography (IAC) clean-up. Low cost, simplicity of operation, speed and minimum consumption of organic solvent were the main advantages of proposed method. The mean contamination of samples was 0.88 μg kg(-1) that was lower than European Legal Limit.

Non-Botrytis grape-rotting fungi responsible for earthy and moldy off-flavors and mycotoxins

The grape microflora is complex and includes filamentous fungi, yeasts and bacteria with different physiological characteristics and effects on wine production. Most studies have focused on the wine microbiota, but a few studies have reported the ecology of grape microorganisms. Some of these organisms - such as non-Botrytis bunch rotting fungi, which greatly influence the safety or sensory quality of wine, due to the production of mycotoxins and off-flavors, respectively - are considered to be spoilage agents. We review here the diversity of filamentous fungi on grapes and the factors influencing their development, such as grape ripening stage, environmental factors (climate, rain and cultivation practices), grape variety and grape health status. We also discuss the pathways by which mycotoxins and off-flavors are produced, the control of the population, the metabolites responsible for wine spoilage and the methods for detecting and characterizing the microorganisms involved.

Differences in the regulation of ochratoxin A by the HOG pathway in Penicillium and Aspergillus in response to high osmolar environments

Penicillium verrucosum, P. nordicum and Aspergillus carbonarius are three important ochratoxin A producing species. P. verrucosum is in addition able to produce citrinin. It has been shown earlier that P. nordicum is adapted to NaCl rich environments like salt rich dry cured foods or even salines. In this organism, the biosynthesis of ochratoxin A plays an adaptive role in this habitat. P. verrucosum generally can be found on cereals, but occasionally also on salt rich dry cured foods. In contrast A. carbonarius usually cannot be found in NaCl rich environments, but it occurs in another environment with high concentration of solutes, e.g., in sugar rich substrates like grapes and grape juices. Usually osmotic challenging conditions activate the HOG MAP kinase signal cascade, which in turn activates various osmo-regulated genes. In the current analysis, it could be demonstrated that in case of P. nordicum and P. verrucosum the NaCl induced production of ochratoxin A is correlated to the phosphorylation status of the HOG MAP kinase. Just the opposite was true for A. carbonarius. In this case, also higher amounts of NaCl in the medium lead to an increased phosphorylation status of HOG, but no increase in ochratoxin biosynthesis was observed. In contrast to the Penicillia, higher NaCl concentrations lead to a rapid cessation of growth by A. carbonarius. High glucose concentrations have much less impact on growth and the phosphorylation of HOG.

Molecular biodiversity of mycotoxigenic fungi that threaten food safety

Fungal biodiversity is one of the most important contributors to the occurrence and severity of mycotoxin contamination of crop plants. Phenotypic and metabolic plasticity has enabled mycotoxigenic fungi to colonize a broad range of agriculturally important crops and to adapt to a range of environmental conditions. New mycotoxin-commodity combinations provide evidence for the ability of fungi to adapt to changing conditions and the emergence of genotypes that confer enhanced aggressiveness toward plants and/or altered mycotoxin production profiles. Perhaps the most important contributor to qualitative differences in mycotoxin production among fungi is variation in mycotoxin biosynthetic genes. Molecular genetic and biochemical analyses of toxigenic fungi have elucidated specific differences in biosynthetic genes that are responsible for intra- and inter-specific differences in mycotoxin production. For Aspergillus and Fusarium, the mycotoxigenic genera of greatest concern, variation in biosynthetic genes responsible for production of individual families of mycotoxins appears to be the result of evolutionary adaptation. Examples of such variation have been reported for: a) aflatoxin biosynthetic genes in Aspergillus flavus and Aspergillus parasiticus; b) trichothecene biosynthetic genes within and among Fusarium species; and c) fumonisin biosynthetic genes in Aspergillus and Fusarium species. Understanding the variation in these biosynthetic genes and the basis for variation in mycotoxin production is important for accurate assessment of the risks that fungi pose to food safety and for prevention of mycotoxin contamination of crops in the field and in storage.

Multilocus sequence analysis of Aspergillus Sect. Nigri in dried vine fruits of worldwide origin

Dried vine fruits may be heavily colonized by Aspergillus species. The molecular biodiversity of an Aspergillus population (234 strains) isolated from dried vine fruit samples of worldwide origin were analyzed by investigating four housekeeping gene loci (calmodulin, β-tubulin, elongation factor 1-α, RPB2). Aspergillus Sect. Nigri was dominant and the strains were identified as A. tubingensis (138), A. awamori (38), A. carbonarius (27), A. uvarum (16) and A. niger (11). Four Aspergillus flavus strains were also identified from Chilean raisins. Two clusters closely related to the A. tubingensis species with a significant bootstrap (60% and 99%) were identified as distinct populations. Among the four loci, RPB2 showed the highest genetic variability. This is the first complete study on the worldwide distribution of black Aspergilli occurring on dried vine fruits identified by a molecular approach.

Detection of ochratoxin A in tropical wine and grape juice from Brazil

BACKGROUND

Ochratoxin A (OTA) is the main mycotoxin found in grapes, wines and grape juices and is considered one of the most harmful contaminants to human health. In this study, samples of tropical wines and grape juices from different grape varieties grown in Brazil were analysed for their OTA content by high-performance liquid chromatography.

RESULTS

The detection and quantification limits for OTA were 0.01 and 0.03 µg L(-1) respectively. OTA was detected in 13 (38.24%) of the samples analysed, with concentrations ranging from < 0.03 to 0.62 µg L(-1). OTA was not detected in any of the grape juice samples. Most of the red wine samples proved to be contaminated with OTA (75%), while only one white wine sample was contaminated. However, the OTA levels detected in all samples were well below the maximum tolerable limit (2 µg L(-1)) in wine and grape juice established by the European Community and Brazilian legislature.

CONCLUSION

The results of this study indicate a low risk of exposure to OTA by consumption of tropical wines and grape juices from Brazil.

Multiplex PCR analysis of fumonisin biosynthetic genes in fumonisin-nonproducing Aspergillus niger and A. awamori strains

To determine the genetic basis for loss of fumonisin B2 (FB2) biosynthesis in FB2-nonproducing Aspergillus niger and A. awamori strains, we developed multiplex PCR primer sets to amplify fragments of eight fumonisin biosynthetic pathway (fum) genes. Fragments of all eight fum genes were amplified from FB2-producing A. niger and A. awamori strains; from FB2-nonproducing strains four amplification patterns arose in which one or more fum gene fragments were absent. Southern hybridization analysis of strains yielding patterns 2 and 3 confirmed that loss of FB2 production in A. awamori is associated with gene deletions within the fumonisin biosynthetic gene cluster. In addition, we observed a fifth multiplex amplification pattern in which all eight fum gene fragments appeared. Reverse transcription-PCR analysis of strains yielding pattern 5 showed that the expression of at least one fum gene was reduced relative to expression in FB2-producing A. niger. This suggests that in these strains loss of FB2 production is a result of structural or regulatory mutations that alter gene expression or function. These results demonstrate a diversity of genotypes within FB2-nonproducing A. niger and A. awamori populations and provide tools useful for identifying certain non-toxigenic strains for industrial or ecological applications.

Mycotoxin production by Aspergillus niger aggregate strains isolated from harvested maize in three Portuguese regions

BACKGROUND

Maize is considered one of the crops more susceptible to mycotoxins in the world. Two of the mycotoxins commonly associated with maize are fumonisins and ochratoxin A. Aspergillus niger is a known producer of ochratoxin A and is easily found in maize. Recently, however, A. niger has been reported to produce as well fumonisins, mainly fumonisin B(2).

AIMS

The aim of this study was to isolate A. niger strains from maize samples collected in three Portuguese maize growing regions and to detect the production of both fumonisin B(2) and ochratoxin A.

METHODS

Ninety five maize samples were collected, plated, and all observable Aspergillus section Nigri strains were isolated. Strains were morphologically characterized and mycotoxin production was determined by HPLC-FD.

RESULTS

Isolations resulted in a total of 270 strains of black Aspergillus from 73 samples (77% of the samples). About 14% of those strains were found to produce ochratoxin A and 39% of the strains were found to produce fumonisin B(2).

CONCLUSIONS

An association between the production of these two mycotoxins could not be found and no conclusions could be taken whether the presence of A. niger aggregate strains will increase the risk of maize contamination with fumonisins and more specifically with fumonisin B(2).