Genetic polymorphisms associated to SDHI fungicides resistance in selected Aspergillus flavus strains and relation with aflatoxin production

The mitigative role of novel aflatoxin-degrading enzymes in diverse broiler performance indicators and gut microbiota following the consumption of diets contaminated with aflatoxins

BACKGROUND

This study aims to explore both the toxic effects of aflatoxins (AFs) and the protective effects of degrading enzymes (DE) on broilers exposed to AFs.

RESULTS

The findings reveal that a diet contaminated with 69.15 μg kg-1 of aflatoxin B1 had significant adverse effects on broilers. Specifically, it led to a reduction in average daily gain, dressed yield percentage, half-eviscerated yield with giblet yield percentage, eviscerated yield percentage, as well as serum superoxide dismutase (SOD), glutathione peroxidase activity and liver SOD activity (P < 0.05). Conversely, the diet increased the feed conversion ratio, liver index, serum glutamic oxaloacetic transaminase levels and malondialdehyde levels in both serum and liver (P < 0.05). Additionally, AFs disrupted the intestinal microflora significantly (P < 0.05), altering the relative abundance of Enterococcus, Lactobacillus and Escherichia in broiler jejunum. The addition of DE to AF-contaminated feed mitigated these negative effects and reduced the residues of aflatoxin B1, aflatoxin B2 and aflatoxin M1 in the liver and duodenum (P < 0.05). We also observed that broilers fed the diet pelleted at 80 °C exhibited improved dressing percentage and water holding capacity compared to those on the 75 °C diet.

CONCLUSION

In summary, DE serves as an effective feed additive for mitigating AF contamination in poultry production. © 2024 Society of Chemical Industry.

Characteristics of famoxadone-resistant mutants of Phytophthora litchii and their effect on lychee fruit quality

Lychee downy blight (LDB), a common disease caused by the oomycete Phytophthora litchii, poses a significant threat to both pre- and post-harvest stages, leading to substantial economic losses. Famoxadone, a quinone outside inhibitor fungicide, was registered for controlling LDB in China in 2002. However, limited information is available regarding the risk, mechanism, and impact on lychee fruit quality associated with famoxadone resistance. In this study, we determined the sensitivity of 133 P. litchii isolates to famoxadone, yielding a mean EC50 value of 0.46 ± 0.21 μg/mL. Through fungicide adaption, we derived resistant mutants with M124I and Y131C substitutions in PlCyt b (Cytochrome b in P. litchii) from wild-type isolates. In vitro assessments revealed that the fitness of the resistant mutants was significantly lower compared to the parental isolates. These laboratory findings demonstrate a moderate resistance risk of P. litchii to famoxadone. Molecular docking analyses indicated that the M124I and Y131C alterations disrupted hydrogen bonds and weakened the binding energy between famoxadone and PlCyt b. This indicates that the M124I and Y131C changes do indeed confer famoxadone resistance in P. litchii. Infection caused by famoxadone-resistant mutants exhibited a decreased or comparable impact on the characteristic traits of lychee fruit compared to the sensitive isolate. For future detection of famoxadone-resistant strains, AS-PCR primers were designed based on the M124I substitution.

Aflatoxins Contamination in Feed Commodities: From Occurrence and Toxicity to Recent Advances in Analytical Methods and Detoxification

Synthesized by the secondary metabolic pathway in Aspergilli, aflatoxins (AFs) cause economic and health issues and are culpable for serious harmful health and economic matters affecting consumers and global farmers. Consequently, the detection and quantification of AFs in foods/feeds are paramount from food safety and security angles. Nowadays, incessant attempts to develop sensitive and rapid approaches for AFs identification and quantification have been investigated, worldwide regulations have been established, and the safety of degrading enzymes and reaction products formed in the AF degradation process has been explored. Here, occurrences in feed commodities, innovative methods advanced for AFs detection, regulations, preventive strategies, biological detoxification, removal, and degradation methods were deeply reviewed and presented. This paper showed a state-of-the-art and comprehensive review of the recent progress on AF contamination in feed matrices with the intention of inspiring interests in both academia and industry.

Resistance of Black Aspergilli Species from Grape Vineyards to SDHI, QoI, DMI, and Phenylpyrrole Fungicides

Fungicide applications constitute a management practice that reduces the size of fungal populations and by acting as a genetic drift factor, may affect pathogen evolution. In a previous study, we showed that the farming system influenced the population structure of the Aspergillus section Nigri species in Greek vineyards. The current study aimed to test the hypothesis that the differences in the population structure may be associated with the selection of fungicide-resistant strains within the black aspergilli populations. To achieve this, we determined the sensitivity of 102, 151, 19, and 22 for the A. uvarum, A. tubingensis, A. niger, and A. carbonarious isolates, respectively, originating either from conventionally-treated or organic vineyards to the fungicides fluxapyroxad-SDHIs, pyraclostrobin-QoIs, tebuconazole-DMIs, and fludioxonil-phenylpyrroles. The results showed widespread resistance to all four fungicides tested in the A. uvarum isolates originating mostly from conventional vineyards. In contrast, all the A. tubingensis isolates tested were sensitive to pyraclostrobin, while moderate frequencies of only lowly resistant isolates were identified for tebuconazole, fludioxonil, and fluxapyroxad. Sequencing analysis of the corresponding fungicide target encoding genes revealed the presence of H270Y, H65Q/S66P, and G143A mutations in the sdhB, sdhD, and cytb genes of A. uvarum resistant isolates, respectively. No mutations in the Cyp51A and Cyp51B genes were detected in either the A. uvarum or A. tubingensis isolates exhibiting high or low resistance levels to DMIs, suggesting that other resistance mechanisms are responsible for the observed phenotype. Our results support the initial hypothesis for the contribution of fungicide resistance in the black aspergilli population structure in conventional and organic vineyards, while this is the first report of A. uvarum resistance to SDHIs and the first documentation of H270Y or H65Q/S66P mutations in sdhB, sdhD, and of the G143A mutation in the cytb gene of this fungal species.

Aflatoxins in Cereals and Cereal-Based Products: Occurrence, Toxicity, Impact on Human Health, and Their Detoxification and Management Strategies

Cereals and cereal-based products are primary sources of nutrition across the world. However, contamination of these foods with aflatoxins (AFs), secondary metabolites produced by several fungal species, has raised serious concerns. AF generation in innate substrates is influenced by several parameters, including the substrate type, fungus species, moisture content, minerals, humidity, temperature, and physical injury to the kernels. Consumption of AF-contaminated cereals and cereal-based products can lead to both acute and chronic health issues related to physical and mental maturity, reproduction, and the nervous system. Therefore, the precise detection methods, detoxification, and management strategies of AFs in cereal and cereal-based products are crucial for food safety as well as consumer health. Hence, this review provides a brief overview of the occurrence, chemical characteristics, biosynthetic processes, health hazards, and detection techniques of AFs, along with a focus on detoxification and management strategies that could be implemented for food safety and security.

Design, Synthesis, and Biological Profiles of Novel 1,3,4-Oxadiazole-2-carbohydrazides with Molecular Diversity

To unceasingly expand the molecular diversity of 1,3,4-oxadiazole-2-carbohydrazides, herein, small fragments (including -CH₂-, -OCH₂-, and -SCH₂-) were incorporated into the target compounds to screen out the potential succinate dehydrogenase inhibitors (SDHIs). The bioassay results showed that the antifungal effects (expressed by EC₅₀) against Sclerotinia sclerotiorum, Botryosphaeria dothidea, Fusarium oxysporum, and Colletotrichun higginsianum could reach 1.29 (10a), 0.63 (8h), 1.50 (10i), and 2.09 (10i) μg/mL, respectively, which were slightly lower than those of carbendazim (EC₅₀ were 0.69, 0.13, 0.55, and 0.80 μg/mL, respectively). Especially, compound 10h was extremely bioactive against Gibberella zeae (G. z.) with an EC₅₀ value of 0.45 μg/mL. This outcome was better than that of fluopyram (3.76 μg/mL) and was similar to prochloraz (0.47 μg/mL). In vivo trials against the corn scab (infected by G. z.) showed that compound 10h had control activity of 86.8% at 200 μg/mL, which was better than that of boscalid (79.6%). Further investigations found that compound 10h could inhibit the enzymatic activity of SDH in the G. z. strain with an IC₅₀ value of 3.67 μM, indicating that potential SDHIs might be developed. Additionally, the other biological activities of these molecules were screened simultaneously. The anti-oomycete activity toward Phytophthora infestans afforded a minimal EC₅₀ value of 3.22 μg/mL (10h); compound 4d could strongly suppress the growth of bacterial strains Xanthomonas axonopodis pv. citri and Xanthomonas oryzae pv. oryzae with EC₅₀ values of 3.79 and 11.4 μg/mL, respectively; and compound 10a displayed some insecticidal activity toward Plutella xylostella. Given their multipurpose features, these frameworks could be actively studied as potential pesticide leads.

Burden of Disease Associated with Dietary Exposure to Aflatoxins in China in 2020

Aflatoxins (AFTs), as a group 1 carcinogen, could lead to hepatocellular carcinoma (HCC). Dietary intake is the primary way of AFT exposure in humans. However, the contribution of foodborne AFT intake to the HCC burden remains unknown in recent years in China. Hence, the present study was conducted to estimate the burden of HCC attributed to foodborne AFT exposure by using disability-adjusted life years (DALYs). The risk assessment was used to estimate the incidence of HCC related to AFT exposure. Concentrations of AFTs in peanuts, peanut oil, corn, and corn products were retrieved from literature published between 2010 and 2020 in China. Corresponding daily food consumption data were obtained from two nationwide Chinese surveys. A direct approach was used to calculate DALY and DALY rates to quantify the HCC burden attributed to dietary AFT exposure. The total amount of AFT intake through peanut, peanut oil, corn, and corn products was 4.018 ng/kg bw/day resulting in 0.125 extra HCC cases per year/100,000 persons, corresponding to a DALY number and DALY rate of 21,625.08 and 1.53 per 100,000 population, respectively. Regionally, DALYs were high in Guangxi and Guangdong provinces, corresponding to 5948 and 5595 DALYs. A total of 1.5 DALYs/100,000 were lost due to the AFT exposure. DALYs per 100,000 population were higher in several coastal areas. Though the disease burden of HCC caused by dietary AFTs was low in the Chinese population, a high health risk was found in the residents of some areas with high AFT exposure. AFTs are still a health challenge for the Chinese people.

The research progress in and perspective of potential fungicides: Succinate dehydrogenase inhibitors

Succinate dehydrogenase inhibitors (SDHIs) have become one of the fastest growing classes of new fungicides since entering the market, and have attracted increasing attention as a result of their unique structure, high activity and broad fungicidal spectrum. The mechanism of SDHIs is to inhibit the activity of succinate dehydrogenase, thereby affecting mitochondrial respiration and ultimately killing pathogenic fungi. At present, they have become popular varieties researched and developed by major pesticide companies in the world. In the review, we focused on the mechanism, the history, the representative varieties, structure-activity relationship and resistance of SDHIs. Finally, the potential directions for the development of SDHIs were discussed. It is hoped that this review can strengthen the individuals' understanding of SDHIs and provide some inspiration for the development of new fungicides.

Directed evolution predicts cytochrome b G37V target site modification as probable adaptive mechanism towards the QiI fungicide fenpicoxamid in Zymoseptoria tritici

Acquired resistance is a threat to antifungal efficacy in medicine and agriculture. The diversity of possible resistance mechanisms and highly adaptive traits of pathogens make it difficult to predict evolutionary outcomes of treatments. We used directed evolution as an approach to assess the resistance risk to the new fungicide fenpicoxamid in the wheat pathogenic fungus Zymoseptoria tritici. Fenpicoxamid inhibits complex III of the respiratory chain at the ubiquinone reduction site (Qi site) of the mitochondrially encoded cytochrome b, a different site than the widely used strobilurins which inhibit the same complex at the ubiquinol oxidation site (Q_o site). We identified the G37V change within the cytochrome b Q_i site as the most likely resistance mechanism to be selected in Z. tritici. This change triggered high fenpicoxamid resistance and halved the enzymatic activity of cytochrome b, despite no significant penalty for in vitro growth. We identified negative cross-resistance between isolates harbouring G37V or G143A, a Q_o site change previously selected by strobilurins. Double mutants were less resistant to both QiIs and quinone outside inhibitors compared to single mutants. This work is a proof of concept that experimental evolution can be used to predict adaptation to fungicides and provides new perspectives for the management of QiIs.

Predicted Aflatoxin B1 Increase in Europe Due to Climate Change: Actions and Reactions at Global Level

Climate change (CC) is predicted to increase the risk of aflatoxin (AF) contamination in maize, as highlighted by a project supported by EFSA in 2009. We performed a comprehensive literature search using the Scopus search engine to extract peer-reviewed studies citing this study. A total of 224 papers were identified after step I filtering (187 + 37), while step II filtering identified 25 of these papers for quantitative analysis. The unselected papers (199) were categorized as “actions” because they provided a sounding board for the expected impact of CC on AFB₁ contamination, without adding new data on the topic. The remaining papers were considered as “reactions” of the scientific community because they went a step further in their data and ideas. Interesting statements taken from the “reactions” could be summarized with the following keywords: Chain and multi-actor approach, intersectoral and multidisciplinary, resilience, human and animal health, and global vision. In addition, fields meriting increased research efforts were summarized as the improvement of predictive modeling; extension to different crops and geographic areas; and the impact of CC on fungi and mycotoxin co-occurrence, both in crops and their value chains, up to consumers.