Azole fungicides - understanding resistance mechanisms in agricultural fungal pathogens

Novel yeast-based biosensor for environmental monitoring of tebuconazole

Due to increasing demand for high and stable crop production, human populations are highly dependent on pesticide use for growing and storing food. Environmental monitoring of these agrochemicals is therefore of utmost importance, because of their collateral effects on ecosystem and human health. Even though most current-use analytical methods achieve low detection limits, they require procedures that are too complex and costly for routine monitoring. As such, there has been an increased interest in biosensors as alternative or complementary tools to streamline detection and quantification of environmental contaminants. In this work, we developed a biosensor for environmental monitoring of tebuconazole (TEB), a common agrochemical fungicide. For that purpose, we engineered S. cerevisiae cells with a reporter gene downstream of specific promoters that are expressed after exposure to TEB and characterized the sensitivity and specificity of this model system. After optimization, we found that this easy-to-use biosensor consistently detects TEB at concentrations above 5 μg L-1 and does not respond to realistic environmental concentrations of other tested azoles, suggesting it is specific. We propose the use of this system as a complementary tool in environmental monitoring programs, namely, in high throughput scenarios requiring screening of numerous samples. KEY POINTS: • A yeast-based biosensor was developed for environmental monitoring of tebuconazole. •The biosensor offers a rapid and easy method for tebuconazole detection ≥ 5 μg L-1. •The biosensor is specific to tebuconazole at environmentally relevant concentrations.

Resistance risk assessment of Rhizoctonia solani to four fungicides

BACKGROUND

Hexaconazole, thifluzamide, difenoconazole and azoxystrobin are widely used fungicides for the control of Rhizoctonia solani in China. However, few studies have assessed the sensitivity and resistance risk of R. solani to these four fungicides.

RESULTS

The sensitivities of 126 R. solani isolates to hexaconazole, thifluzamide, difenoconazole and azoxystrobin were determined, with average half maximal effective concentration (EC50) values of 0.0386, 0.0659, 0.663 and 1.508 μg mL-1, respectively. Field resistance monitoring of the four fungicides showed that the three isolates had moderate resistance to difenoconazole. Resistant mutants to the four fungicides were obtained by fungicide adaptation, and resistance could be stably inherited by most mutants. Compared with those of the parent isolates, the biological characteristics of hexaconazole-resistant mutants exhibited enhanced or similar compound fitness index (CFI), whereas most of the other mutants displayed reduced or comparable CFI. There was evidence of positive cross-resistance between hexaconazole and difenoconazole. In the presence of fungicides, the expression of the CYP51 genes in hexaconazole- and difenoconazole-resistant mutants significantly increased, the expression of SDH genes in thifluzamide-resistant mutants significantly decreased, and the expression of the Cyt b gene in azoxystrobin-resistant mutants did not significantly change.

CONCLUSION

Based on these data, we speculated that R. solani had a low-to-medium resistance risk to four fungicides. The change of target gene expression may be one of the reasons for fungicide resistance in R. solani. This study provides a theoretical basis for monitoring resistance emergence and developing resistance management strategies to control R. solani. © 2024 Society of Chemical Industry.

Induction of drug metabolizing enzyme and drug transporter expression by antifungal triazole pesticides in human HepaSH hepatocytes

Triazole pesticides are widely used fungicides, to which humans are rather highly exposed. They are known to activate drug-sensing receptors regulating expression of hepatic drug metabolizing enzymes and drug transporters, thus suggesting that the hepatic drug detoxification system is modified by these agrochemicals. To investigate this hypothesis, the effects of 9 triazole fungicides towards expression of drug metabolizing enzymes and transporters were characterized in cultured human HepaSH cells, that are human hepatocytes deriving from chimeric humanized liver TK-NOG mice. Most of triazoles used at 10 μM were found to act as inducers of cytochrome P-450 (CYP) 1A1, CYP1A2, CYP2B6, CYP3A4 and UDP-glucuronosyltransferase 1A1 mRNA levels and of CYP3A4 protein; some triazoles also enhanced mRNA expression of the canalicular transporters P-glycoprotein/MDR1, multidrug resistance-associated protein 2 and breast cancer resistance protein. Triazoles however concomitantly inhibited CYP2B6 and CYP3A4 activities and thus appeared as dual regulators of these CYPs, being both inducers of their expression and inhibitors of their activity. The inducing effect however predominated, at least for bromuconazole, propiconazole and tebuconazole. Bromuconazole was moreover predicted to enhance CYP2B6 and CYP3A4 expression in humans exposed to this fungicide in a chronic, acute or occupational context. These data demonstrate that key-actors of the human hepatic detoxification system are impacted by triazole pesticides, which may have to be considered for the risk assessment of these agrochemicals. They additionally highlight that the use of human HepaSH cells as surrogates to primary human hepatocytes represents an attractive and promising way for studying hepatic effects of environmental chemicals.

CbCyp51-Mediated Demethylation Inhibitor Resistance Is Modulated by Codon Bias

Cercospora leaf spot, caused by the fungus Cercospora beticola, is the most destructive foliar disease of sugarbeet worldwide. Resistance to the sterol demethylation inhibitor (DMI) fungicide tetraconazole has been previously correlated with synonymous and nonsynonymous mutations in CbCyp51. Here, we extend these analyses to the DMI fungicides prothioconazole, difenoconazole, and mefentrifluconazole in addition to tetraconazole to confirm whether the synonymous and nonsynonymous mutations at amino acid positions 144 and 170 are associated with resistance to these fungicides. Nearly half of the 593 isolates of C. beticola collected in the Red River Valley of North Dakota and Minnesota in 2021 were resistant to all four DMIs. Another 20% were resistant to tetraconazole and prothioconazole but sensitive to difenoconazole and mefentrifluconazole. A total of 13% of isolates were sensitive to all DMIs tested. We found five CbCyp51 haplotypes and associated them with phenotypes to the four DMIs. The most predominant haplotype (E170_A/L144F_C) correlated with resistance to all four DMIs with up to 97.6% accuracy. The second most common haplotype (E170_A/L144) consisted of isolates associated with resistance phenotypes to tetraconazole and prothioconazole while also exhibiting sensitive phenotypes to difenoconazole and mefentrifluconazole with up to 98.4% accuracy. Quantitative PCR did not identify differences in CbCyp51 expression between haplotypes. This study offers an understanding of the importance of codon usage in fungicide resistance and provides crop management acuity for fungicide application decision-making.

Resistance Mechanisms of Plant Pathogenic Fungi to Fungicide, Environmental Impacts of Fungicides, and Sustainable Solutions

The significant reduction in agricultural output and the decline in product quality are two of the most glaring negative impacts caused by plant pathogenic fungi (PPF). Furthermore, contaminated food or transit might introduce mycotoxins produced by PPF directly into the food chain. Eating food tainted with mycotoxin is extremely dangerous for both human and animal health. Using fungicides is the first choice to control PPF or their toxins in food. Fungicide resistance and its effects on the environment and public health are becoming more and more of a concern, despite the fact that chemical fungicides are used to limit PPF toxicity and control growth in crops. Fungicides induce target site alteration and efflux pump activation, and mutations in PPF result in resistance. As a result, global trends are shifting away from chemically manufactured pesticides and toward managing fungal plant diseases using various biocontrol techniques, tactics, and approaches. However, surveillance programs to monitor fungicide resistance and their environmental impact are much fewer compared to bacterial antibiotic resistance surveillance programs. In this review, we discuss the PPF that contributes to disease development in plants, the fungicides used against them, factors causing the spread of PPF and the emergence of new strains, the antifungal resistance mechanisms of PPF, health, the environmental impacts of fungicides, and the use of biocontrol agents (BCAs), antimicrobial peptides (AMPs), and nanotechnologies to control PPF as a safe and eco-friendly alternative to fungicides.

Advancements in the nanodelivery of azole-based fungicides to control oil palm pathogenic fungi

The cultivation of oil palms is of great importance in the global agricultural industry due to its role as a primary source of vegetable oil with a wide range of applications. However, the sustainability of this industry is threatened by the presence of pathogenic fungi, particularly Ganoderma spp., which cause detrimental oil palm disease known as basal stem rot (BSR). This unfavorable condition eventually leads to significant productivity losses in the harvest, with reported yield reductions of 50-80 % in severely affected plantations. Azole-based fungicides offer potential solutions to control BSR, but their efficacy is hampered by limited solubility, penetration, distribution, and bioavailability. Recent advances in nanotechnology have paved the way for the development of nanosized delivery systems. These systems enable effective fungicide delivery to target pathogens and enhance the bioavailability of azole fungicides while minimising environmental and human health risks. In field trials, the application of azole-based nanofungicides resulted in up to 75 % reduction in disease incidence compared to conventional fungicide treatments. These innovations offer opportunities for the development of sustainable agricultural practices. This review highlights the importance of oil palm cultivation concerning the ongoing challenges posed by pathogenic fungi and examines the potential of azole-based fungicides for disease control. It also reviews recent advances in nanotechnology for fungicide delivery, explores the mechanisms behind these nanodelivery systems, and emphasises the opportunities and challenges associated with azole-based nanofungicides. Hence, this review provides valuable insights for future nanofungicide development in effective oil palm disease control.

Deciphering the mechanisms involved in reduced sensitivity to azoles and fengycin lipopeptide in Venturia inaequalis

Apple scab, caused by the hemibiotrophic fungus Venturia inaequalis, is currently the most common and damaging disease in apple orchards. Two strains of V. inaequalis (S755 and Rs552) with different sensitivities to azole fungicides and the bacterial metabolite fengycin were compared to determine the mechanisms responsible for these differences. Antifungal activity tests showed that Rs552 had reduced sensitivity to tebuconazole and tetraconazole, as well as to fengycin alone or in a binary mixture with other lipopeptides (iturin A, pumilacidin, lichenysin). S755 was highly sensitive to fengycin, whose activity was close to that of tebuconazole. Unlike fengycin, lipopeptides from the iturin family (mycosubtilin, iturin A) had similar activity on both strains, while those from the surfactin family (lichenysin, pumilacidin) were not active, except in binary mixtures with fengycin. The activity of lipopeptides varies according to their family and structure. Analyses to determine the difference in sensitivity to azoles (which target the CYP51 enzyme involved in the ergosterol biosynthesis pathway) showed that the reduced sensitivity in Rs552 is linked to (i) a constitutive increased expression of the Cyp51A gene caused by insertions in the upstream region and (ii) greater efflux by membrane pumps with the involvement of ABC transporters. Microscopic observations revealed that fengycin, known to interact with plasma membranes, induced morphological and cytological changes in cells from both strains. Sterol and phospholipid analyses showed a higher level of ergosta-7,22-dien-3-ol and a lower level of PI(C16:0/C18:1) in Rs552 compared with S755. These differences could therefore influence the composition of the plasma membrane and explain the differential sensitivity of the strains to fengycin. However, the similar antifungal activities of mycosubtilin and iturin A in the two strains indirectly indicate that sterols are probably not involved in the fengycin resistance mechanism. This leads to the conclusion that different mechanisms are responsible for the difference in susceptibility to azoles or fengycin in the strains studied.

Environmental microbiome, human fungal pathogens, and antimicrobial resistance

Traditionally, antifungal resistance (AFR) has received much less attention compared with bacterial resistance to antibiotics. However, global changes, pandemics, and emerging new fungal infections have highlighted global health consequences of AFR. The recent report of the World Health Organisation (WHO) has identified fungal priority pathogens, and recognised AFR among the greatest global health threats. This is particularly important given the significant increase in fungal infections linked to climate change and pandemics. Environmental factors play critical roles in AFR and fungal infections, as many clinically relevant fungal pathogens and AFR originate from the environment (mainly soil). In addition, the environment serves as a potential rich source for the discovery of new antifungal agents, including mycoviruses and bacterial probiotics, which hold promise for effective therapies. In this article, we summarise the environmental pathways of AFR development and spread among high priority fungal pathogens, and propose potential mechanisms of AFR development and spread. We identify a research priority list to address key knowledge gaps in our understanding of environmental AFR. Further, we propose an integrated roadmap for predictive risk management of AFR that is critical for effective surveillance and forecasting of public health outcomes under current and future climatic conditions.

Enhancing Corn (Zea mays L.) Productivity under Varying Water Regimes with At-Plant Application of Xyway Fungicide

A fungicide's ingredients can play a physiological role in crop water-management decisions. Our greenhouse study in 2021 demonstrated that Xyway LFR@FMC at-plant fungicide can significantly improve water-saving potential in corn. In 2022 and 2023, a field study was conducted to validate this finding. The 1.11 L ha-1 of Xyway LFR@FMC and no-fungicide/check were the main plot effects. Three water regimes, high (HI) and low (LO) numbers of irrigation events and rainfed (RF), were the subplot effect. Plants treated with Xyway LFR@FMC had significantly higher plant height, stem diameter, and leaf water potential (LWP), and had 11.9, 13.4, and 18.3% higher yield under RF, LO, and HI, respectively, in 2022. In 2023, there were no significant differences for the yield components and growth parameters when the combined effect of fungicide treatments and water regimes was considered. However, plants treated with the fungicide had a higher number of rows per ear, kernel number per row, and cob diameter compared to the check. There was no significant separation for yield among the water regimes in 2023, but the crop yield was overall higher for the fungicide-treated plots. Our results indicate that Xyway LFR@FMC fungicide has the potential to improve plant growth and protect the yield when limited water is applied.

Chiral Fluorescent Antifungal Azole Probes Detect Resistance, Uptake Dynamics, and Subcellular Distribution in Candida Species

Azoles are essential for fungal infection treatment, yet the increasing resistance highlights the need for innovative diagnostic tools and strategies to revitalize this class of antifungals. We developed two enantiomers of a fluorescent antifungal azole probe (1 S and 1 R ), analyzing 60 Candida strains via live-cell microscopy. A database of azole distribution images in strains of Candida albicans, Candida glabrata, and Candida parapsilosis, among the most important pathogenic Candida species, was established and analyzed. This analysis revealed distinct populations of yeast cells based on the correlation between fluorescent probe uptake and cell diameter. Varied uptake levels and subcellular distribution patterns were observed in C. albicans, C. glabrata, and C. parapsilosis, with the latter displaying increased localization to lipid droplets. Comparison of the more potent fluorescent antifungal azole probe enantiomer 1 S with the moderately potent enantiomer 1 R highlighted time-dependent differences in the uptake profiles. The former displayed a marked elevation in uptake after approximately 150 min, indicating the time required for significant cell permeabilization to occur and its association with the azole's antifungal activity potency. Divergent uptake levels between susceptible and high efflux-based azole-resistant strains were detected, offering a rapid diagnostic approach for identifying azole resistance. This study highlights unique insights achievable through fluorescent antifungal azole probes, unraveling the complexities of azole resistance, subcellular dynamics, and uptake within fungal pathogens.

Occurrence and risk assessment of azole fungicides during the urban water cycle: A year-long study along the Yangtze River, China

Azole fungicides (AFs) play an important role in the prevention and treatment of fungal diseases in agricultural crops. However, limited studies are addressing the fate and ecological risk of AFs in the urban water cycle at a large watershed scale. To address this gap, we investigated the spatiotemporal distribution and ecological risk of twenty AFs in the lower reaches of the Yangtze River across four seasons. Carbendazim (CBA), tebuconazole (TBA), tricyclazole (TCA), and propiconazole (PPA) were found to be the dominant compounds. Their highest concentrations were measured in January (188.3 ng/L), and November (2197.1 ng/L), July (162.0 ng/L), and November (1801.9 ng/L), respectively. The comparison between wastewater treatment plants (WWTPs) effluents and surface water suggested that industrial WWTPs are major sources of AFs in the Yangtze River. In particular, TBA and PPA were found to be the most recalcitrant AFs in industrial WWTPs, while difenoconazole (DFA) was found to be the most potent pollutant in municipal WWTPs, with an average removal rate of less than 60%. The average risk quotient (RQ) for the entire AFs was 6.45 in the fall, which was higher than in January (0.98), April (0.61), and July (0.40). This indicates that AFs in surface water posed higher environmental risks during the dry season. Additionally, the exposure risk of AFs via drinking water for sensitive populations deserves more attention. This study provides benchmark data on the occurrence of AFs in the lower reaches of the Yangtze River, and offers suggestions for better reduction of AFs.

Epoxiconazole altered hepatic metabolism in adult zebrafish based on transcriptomic analysis

Epoxiconazole (EPX) is a triazole fungicide, which has been widely used in pest control of cereal crops. However, its extensive use has led to concerning levels of residue in water bodies, posing substantial risks to aquatic life. In this study, we characterized the toxicological effects of EPX on 6-month-old male and female zebrafish at 70 and 700 μg/L, respectively. The results revealed that EPX exposure markedly increased both body length and weight in zebrafish of both sexes, consequently elevating their condition factor. Besides, EPX exposure resulted in notable alterations in hepatic histopathology. These changes included loosened hepatocyte structure, ballooning degeneration, nucleolysis, and disappearance of cell line, with male zebrafish exhibiting more severe damage. High concentration of EPX also significantly increased hepatic lipid accumulation in male zebrafish, as well as increased hepatic triglyceride (TG) levels. Correspondingly, there was a notable alteration in the transcription of genes including cyp51, hmgcr, and PPAR-γ, which associated with cholesterol and lipid metabolism. Interestingly, with the hepatic transcriptomic analysis, high concentration of EPX produced 195 upregulated and 107 downregulated differential expression genes. Both KEGG and GO analyses identified significant enrichment of these genes in lipid and amino acid metabolism pathways. Notably, some key genes involved in the steroid synthesis pathway were marked upregulated. In addition, molecular docking study confirmed that EPX could bind CYP51 protein well (△G = -7.7 kcal/mol). Taken together, these findings demonstrated the multiple toxic effects of EPX on adult zebrafish.

Azoles activate type I and type II programmed cell death pathways in crop pathogenic fungi

Triazoles are widely used to control pathogenic fungi. They inhibit the ergosterol biosynthetic pathway, but the precise mechanisms leading to fungicidal activities in many fungal pathogens are poorly understood. Here, we elucidate the mode of action of epoxiconazole and metconazole in the wheat pathogen Zymoseptoria tritici and the rice blast fungus Magnaporthe oryzae. We show that both azoles have fungicidal activity and reduce fluidity, but not integrity, of the plasma membrane. This impairs localisation of Cdc15-like F-BAR proteins, resulting in defective actin ring assembly and incomplete septation. However, mutant studies and pharmacological experiments in vitro and in planta show that azole lethality is due to a combination of reactive oxygen species-induced apoptosis and macroautophagy. Simultaneous inhibition of both programmed cell death pathways abolishes azole-induced cell death. Other classes of ergosterol biosynthesis inhibitors also induce apoptosis and macroautophagy, suggesting that activation of these two cell death pathways is a hallmark of ergosterol synthesis-targeting fungicides. This knowledge will inform future crop protection strategies.

Synthesis, biological evaluation, and molecular docking of novel ferulic acid derivatives containing a 1,3,4-oxadiazole thioether and trifluoromethyl pyrimidine skeleton

In this study, 24 novel ferulic acid derivatives containing 1,3,4-oxadiazole thioether and trifluoromethyl pyrimidine were designed and synthesized. Bioactivity assay showed that some of the target compounds exhibited moderate to good antifungal activity against Botryosphaeria dothidea BD), Phomopsis sp. (PS), Botrytis cinerea (BC), Fusarium spp. (FS), Fusarium graminearum (FG), and Colletotrichum sp. (CS). Especially, compound 6f demonstrated superior antifungal activity against Phomopsis sp., with an EC50 value of 12.64 μg mL-1, outperforming pyrimethanil (35.16 μg mL-1) and hymexazol (27.01 μg mL-1). Meanwhile, compound 6p showed strong antibacterial activity against X. axonopodis pv. citri (XAC) in vitro, with an inhibition ratio of 85.76%, which was higher than thiodiazole copper's 76.59% at 100 μg mL-1. Furthermore, molecular docking simulations elucidated that compound 6f engaged in hydrogen bonding with the succinate dehydrogenase (SDH) enzyme at SER-17, SER-39, ARG-14 and ARG-43 sites, clarifying its mode of action. This study highlights the potential of these novel ferulic acid derivatives as promising agents for controlling fungal and bacterial threats to plant health. To the best of our knowledge, this study represents the first report on the antifungal and antibacterial properties of ferulic acid derivatives containing 1,3,4-oxadiazole thioether and trifluoromethyl pyrimidine skeleton.

Triazole resistance in Aspergillus fumigatus isolated from a tomato production environment exposed to propiconazole

The emergence of azole-resistant Aspergillus fumigatus (ARAf) across the world is an important public health concern. We sought to determine if propiconazole, a demethylase inhibitor (DMI) fungicide, exerted a selective pressure for ARAf in a tomato production environment following multiple exposures to the fungicide. A tomato field trial was established in 2019 and propiconazole was applied weekly until harvest. Soil, leaf, and fruit (when present) samples were collected at baseline and after each propiconazole application. A. fumigatus isolates (n, 178) were recovered and 173 were tested for susceptibility to itraconazole, posaconazole, voriconazole, and propiconazole in accordance with CLSI M38 guidelines. All the isolates were susceptible to medical triazoles and the propiconazole MIC ranged from 0.25 to 8 mg/L. A linear regression model was fitted that showed no longitudinal increment in the log2-fold azole MIC of the isolates collected after each propiconazole exposure compared to the baseline isolates. AsperGenius real-time multiplex assay ruled out TR34/L98H and TR46/Y121F/T289A cyp51A resistance markers in these isolates. Sequencing of a subset of isolates (n, 46) demonstrated widespread presence of F46Y/M172V/E427K and F46Y/M172V/N248T/D255E/E427K cyp51A mutations previously associated with reduced susceptibility to triazoles.

IMPORTANCE

The agricultural use of azole fungicides to control plant diseases has been implicated as a major contributor to ARAf infections in humans. Our study did not reveal imposition of selection pressure for ARAf in a vegetable production system. However, more surveillance studies for ARAf in food crop production and other environments are warranted in understanding this public and One Health issue.

Metal-Organic Framework-Enabled Sustainable Agrotechnologies: An Overview of Fundamentals and Agricultural Applications

With aggravated abiotic and biotic stresses from increasing climate change, metal-organic frameworks (MOFs) have emerged as versatile toolboxes for developing environmentally friendly agrotechnologies aligned with agricultural practices and safety. Herein, we have explored MOF-based agrotechnologies, focusing on their intrinsic properties, such as structural and catalytic characteristics. Briefly, MOFs possess a sponge-like porous structure that can be easily stimulated by the external environment, facilitating the controlled release of agrochemicals, thus enabling precise delivery of agrochemicals. Additionally, MOFs offer the ability to remove or degrade certain pollutants by capturing them within their pores, facilitating the development of MOF-based remediation technologies for agricultural environments. Furthermore, the metal-organic hybrid nature of MOFs grants them abundant catalytic activities, encompassing photocatalysis, enzyme-mimicking catalysis, and electrocatalysis, allowing for the integration of MOFs into degradation and sensing agrotechnologies. Finally, the future challenges that MOFs face in agrotechnologies were proposed to promote the development of sustainable agriculture practices.

Molecular Mechanisms and Biological Characteristics of Botrytis cinerea Field Isolate Resistance to Pyrisoxazole in Liaoning Province

Botrytis cinerea is a broad-host-range necrotrophic phytopathogen responsible for serious diseases in leading crops worldwide. The novel sterol 14α-demethylase inhibitor (DMI) pyrisoxazole was recently registered for the control of tomato gray mold caused by B. cinerea in China. One hundred fifty-seven isolates of B. cinerea were collected from tomato greenhouses in 14 cities of Liaoning Province from 2016 to 2021 and examined for sensitivity to pyrisoxazole, with a mean EC50 value of 0.151 μg/ml. Three highly resistant isolates, XD-5, DG-4, and GQ-3, were screened, and the EC50 values were 0.734, 0.606, and 0.639 μg/ml with corresponding resistance factors of 12.88, 10.63, and 11.21, respectively. Compared with field-sensitive strains, the highly resistant isolate XD-5 exhibited fitness defects in traits, including mycelial growth, conidial production, and pathogenicity, but DG-4 and GQ-3 did not experience fitness costs. Positive cross-resistance was observed only between pyrisoxazole and the DMIs tebuconazole and prochloraz but not between pyrisoxazole and the non-DMIs iprodione, procymidone, pyrimethanil, fludioxonil, fluazinam, and fluopyram. Sequence alignment of the CYP51 gene indicated that three point mutations were observed in the highly resistant mutant, namely, V24I in XD-5, G461S in GQ-3, and R464K in DG-4. When exposed to pyrisoxazole, the induced expression levels of the ABC transporter AtrD and MFS transporter Mfs1 increased in the resistant isolates compared with those in the sensitive isolates, whereas the expression level of the CYP51 gene did not change significantly. Molecular docking suggested that the G461S and R464K mutations both led to a decrease in the binding energy between CYP51 and pyrisoxazole, whereas no change was found with the V24I mutation. Thus, two point mutations in the CYP51 protein combined with induced expression of the Mfs1 and AtrD genes appeared to mediate the pyrisoxazole resistance of the highly resistant mutants DG-4 and GQ-3, while the overexpression of the Mfs1 and AtrD genes was responsible for the highly resistant mutant XD-5.

Design, Synthesis, and Fungicidal Activities of Novel N-(Pyrazol-5-yl)benzamide Derivatives Containing a Diphenylamine Moiety

To accelerate the development of novel fungicides, a variety of N-(pyrazol-5-yl)benzamide derivatives with a diphenylamine moiety were designed and synthesized using a pharmacophore recombination strategy based on the structure of pyrazol-5-yl-aminophenyl-benzamides. The bioassay results demonstrated that most of the target compounds had excellent in vitro antifungal activities against Sclerotinia sclerotiorum, Valsa mali, and Botrytis cinerea. In particular, compound 5IIIh exhibited remarkable activity against S. sclerotiorum (EC50 = 0.37 mg/L), which was similar to that of fluxapyroxad (EC50 = 0.27 mg/L). In addition, compound 5IIIc (EC50 = 1.32 mg/L) was observed to be more effective against V. mali than fluxapyroxad (EC50 = 12.8 mg/L) and comparable to trifloxystrobin (EC50 = 1.62 mg/L). Furthermore, compound 5IIIh demonstrated remarkable in vivo protective antifungal properties against S. sclerotiorum, with an inhibition rate of 96.8% at 100 mg/L, which was close to that of fluxapyroxad (99.6%). Compounds 5IIIc (66.7%) and 5IIIh (62.9%) exhibited good in vivo antifungal effects against V. mali at 100 mg/L, which were superior to that of fluxapyroxad (11.1%) but lower than that of trifloxystrobin (88.9%). The succinate dehydrogenase (SDH) enzymatic inhibition assay was conducted to confirm the mechanism of action. Molecular docking analysis further revealed that compound 5IIIh has significant hydrogen-bonding, π-π, and p-π conjugation interactions with ARG 43, SER 39, TRP 173, and TYR 58 in the binding site of SDH, and the binding mode was similar to that of the commercial fungicide fluxapyroxad. All of the results suggest that compound 5IIIh could be a potential SDH inhibitor, offering a valuable reference for future studies.

cyp51A mutations, protein modeling, and efflux pump gene expression reveals multifactorial complexity towards understanding Aspergillus section Nigri azole resistance mechanism

Black Aspergillus species are the most common etiological agents of otomycosis, and pulmonary aspergillosis. However, limited data is available on their antifungal susceptibility profiles and associated resistance mechanisms. Here, we determined the azole susceptibility profiles of black Aspergillus species isolated from the Indian environment and explored the potential resistance mechanisms through cyp51A gene sequencing, protein homology modeling, and expression analysis of selected genes cyp51A, cyp51B, mdr1, and mfs based on their role in imparting resistance against antifungal drugs. In this study, we have isolated a total of 161 black aspergilli isolates from 174 agricultural soil samples. Isolates had variable resistance towards medical azoles; approximately 11.80%, 3.10%, and 1.24% of isolates were resistant to itraconazole (ITC), posaconazole (POS), and voriconazole (VRC), respectively. Further, cyp51A sequence analysis showed that non-synonymous mutations were present in 20 azole-resistant Aspergillus section Nigri and 10 susceptible isolates. However, Cyp51A homology modeling indicated insignificant protein structural variations because of these mutations. Most of the isolates showed the overexpression of mdr1, and mfs genes. Hence, the study concluded that azole-resistance in section Nigri cannot be attributed exclusively to the cyp51A gene mutation or its overexpression. However, overexpression of mdr1 and mfs genes may have a potential role in drug resistance.

Mechanisms of methyl 2-methylbutyrate suppression on Aspergillus flavus growth and aflatoxin B1 biosynthesis

Aspergillus flavus and subsequently produced carcinogenic aflatoxins frequently contaminate postharvest food crops, resulting in a threat to global food safety. Chemical preservatives are currently the main antifungal agents. However, fungal resistance effect, biological toxicity, and environmental contamination limit their practical applications. The application of natural volatile organic compounds has great potential for controlling fungal and mycotoxin contamination of postharvest food crops. This study therefore investigated the antifungal and anti-aflatoxigenic activities of the volatile compound, methyl 2-methylbutyrate (M2M), against Aspergillus flavus and its potential mechanisms. M2M effectively inhibited A. flavus mycelia growth, with a minimum inhibitory concentration of 2.0 μL/mL. Moreover, M2M also suppressed aflatoxin production, sclerotia production, and the pathogenicity on peanut and corn flour. RNA-Seq results showed that 2899 differentially expressed genes (DEGs), and DEGs involved in ergosterol synthesis, cell wall structure, glycolysis, citric acid cycle, mitogen activated protein kinase signaling pathway, DNA replication, and aflatoxin biosynthesis, were down-regulated in A. flavus. Further studies showed that M2M strongly damaged the cell membrane and cell wall integrity, reduced ATP levels, and induced reactive oxygen species (ROS) accumulation and DNA damage. Notably, a GATA type zinc finger transcription factor, AfSreA (AFLA_132440), which is essential for A. flavus growth and aflatoxin production, was identified. The growth and aflatoxin yield in the ΔAfSreA strain decreased by 94.94 % and 71.82 %, respectively. Additionally, deletion of AfSreA destroyed cell wall integrity and decreased expressions of genes involved in aflatoxin biosynthesis. Taken together, our results identified the antifungal and anti-aflatoxigenic mechanisms of M2M against A. flavus, and confirmed the potential of M2M in protecting peanut and corn from fungal contamination.

Resistance risk assessment of mefentrifluconazole in Corynespora cassiicola and the control of cucumber target spot by a two-way mixture of mefentrifluconazole and prochloraz

The cucumber target spot, caused by Corynespora cassiicola, is a major cucumber disease in China. Mefentrifluconazole, a new triazole fungicide, exhibits remarkable efficacy in controlling cucumber target spot. However, the resistance risk and mechanism remain unclear. In this study, the inhibitory activity of mefentrifluconazole against 101 C. cassiicola isolates was determined, and the results indicated that the EC50 values ranged between 0.15 and 12.85 μg/mL, with a mean of 4.76 μg/mL. Fourteen mefentrifluconazole-resistant mutants of C. cassiicola were generated from six parental isolates in the laboratory through fungicide adaptation or UV irradiation. The resistance was relatively stable after ten consecutive transfers on a fungicide-free medium. No cross-resistance was observed between mefentrifluconazole and pyraclostrobin, fluopyram, prochloraz, mancozeb, or difenoconazole. Investigations into the biological characteristics of the resistant mutants revealed that six resistant mutants exhibited an enhanced compound fitness index (CFI) compared to the parental isolates, while others displayed a reduced or comparable CFI. The overexpression of CcCYP51A and CcCYP51B was detected in the resistant mutants, regardless of the presence or absence of mefentrifluconazole. Additionally, a two-way mixture of mefentrifluconazole and prochloraz at a concentration of 7:3 demonstrated superior control efficacy against the cucumber target spot, achieving a protection rate of 80%. In conclusion, this study suggests that the risk of C. cassiicola developing resistance to mefentrifluconazole is medium, and the overexpression of CcCYP51A and CcCYP51B might be associated with mefentrifluconazole resistance in C. cassiicola. The mefentrifluconazole and prochloraz two-way mixture presented promising control efficacy against the cucumber target spot.

Hotspot mutations and genomic expansion of ERG11 are major mechanisms of azole resistance in environmental and human commensal isolates of Candida tropicalis

OBJECTIVES

Infections caused by azole-resistant Candida tropicalis strains are increasing in clinical settings. The reason for this epidemical change and the mechanisms of C. tropicalis azole resistance are not fully understood.

METHODS

In this study, we performed biological and genomic analyses of 239 C. tropicalis strains, including 115 environmental and 124 human commensal isolates.

RESULTS

Most (99.2%) of the isolates had a baseline diploid genome. The strains from both environmental and human niches exhibit similar abilities to survive under stressful conditions and produce secreted aspartic proteases. However, the human commensal isolates exhibited a stronger ability to filament than the environmental strains. We found that 19 environmental isolates (16.5%) and 24 human commensal isolates (19.4%) were resistant to fluconazole. Of the fluconazole-resistant strains, 37 isolates (86.0%) also exhibited cross-resistance to voriconazole. Whole-genome sequencing and phylogenetic analyses revealed that both environmental and commensal isolates were widely distributed in a number of genetic clusters, but the two populations exhibited a close genetic association. The majority of fluconazole-resistant isolates were clustered within a single clade (X).

CONCLUSIONS

The combination of hotspot mutations (Y132F and S154F) and genomic expansion of ERG11, which encodes the azole target lanosterol 14-α-demethylase and represents a major target of azole drugs, was a major mechanism for the development of azole resistance. The isolates carrying both hotspot mutations and genomic expansion of ERG11 exhibited cross-resistance to fluconazole and voriconazole. Moreover, the azole-resistant isolates from both the environmental and human commensal niches showed similar genotypes.

The rapid emergence of antifungal-resistant human-pathogenic fungi

During recent decades, the emergence of pathogenic fungi has posed an increasing public health threat, particularly given the limited number of antifungal drugs available to treat invasive infections. In this Review, we discuss the global emergence and spread of three emerging antifungal-resistant fungi: Candida auris, driven by global health-care transmission and possibly facilitated by climate change; azole-resistant Aspergillus fumigatus, driven by the selection facilitated by azole fungicide use in agricultural and other settings; and Trichophyton indotineae, driven by the under-regulated use of over-the-counter high-potency corticosteroid-containing antifungal creams. The diversity of the fungi themselves and the drivers of their emergence make it clear that we cannot predict what might emerge next. Therefore, vigilance is critical to monitoring fungal emergence, as well as the rise in overall antifungal resistance.

Antifungal resistance, combinations and pipeline: oh my!

Invasive fungal infections are a strong contributor to healthcare costs, morbidity and mortality, especially amongst hospitalized patients. Historically, Candida was responsible for approximately 15% of all nosocomial bloodstream infections. In the past 10 years, the epidemiology of Candida species has altered, with increasing prevalence of resistant species. With rising fungal resistance, especially in Candida spp., the demand for novel antifungal therapies has exponentially increased over the last decade. Newer antifungal agents have become an attractive option for patients needing long-term therapy for infections or those requiring antifungal prophylaxis. Despite advances in coverage of non-Candida pathogens with newer agents, clinical scenarios involving multidrug-resistant fungal pathogens continue to arise in practice. Combination antifungal therapy can lead to a host of side-effects, some of which can be drug limiting. Additional antifungal therapies with enhanced fungal spectrum of activity and decreased rates of adverse effects are warranted. Fosmanogepix, ibrexafungerp, olorofim and rezafungin may help fill some of these gaps in the antifungal armamentarium. This article is part of the Challenges and strategies in the management of invasive fungal infections Special Issue: https://www.drugsincontext.com/special_issues/challenges-and-strategies-in-the-management-of-invasive-fungal-infections.

Drug-Resistant Aspergillus spp.: A Literature Review of Its Resistance Mechanisms and Its Prevalence in Europe

Infections due to the Aspergillus species constitute an important challenge for human health. Invasive aspergillosis represents a life-threatening disease, mostly in patients with immune defects. Drugs used for fungal infections comprise amphotericin B, triazoles, and echinocandins. However, in the last decade, an increased emergence of azole-resistant Aspergillus strains has been reported, principally belonging to Aspergillus fumigatus species. Therefore, both the early diagnosis of aspergillosis and its epidemiological surveillance are very important to establish the correct antifungal therapy and to ensure a successful patient outcome. In this paper, a literature review is performed to analyze the prevalence of Aspergillus antifungal resistance in European countries. Amphotericin B resistance is observed in 2.6% and 10.8% of Aspergillus fumigatus isolates in Denmark and Greece, respectively. A prevalence of 84% of amphotericin B-resistant Aspergillus flavus isolates is reported in France, followed by 49.4%, 35.1%, 21.7%, and 20% in Spain, Portugal, Greece, and amphotericin B resistance of Aspergillus niger isolates is observed in Greece and Belgium with a prevalence of 75% and 12.8%, respectively. The prevalence of triazole resistance of Aspergillus fumigatus isolates, the most studied mold obtained from the included studies, is 0.3% in Austria, 1% in Greece, 1.2% in Switzerland, 2.1% in France, 3.9% in Portugal, 4.9% in Italy, 5.3% in Germany, 6.1% in Denmark, 7.4% in Spain, 8.3% in Belgium, 11% in the Netherlands, and 13.2% in the United Kingdom. The mechanism of resistance is mainly driven by the TR34/L98H mutation. In Europe, no in vivo resistance is reported for echinocandins. Future studies are needed to implement the knowledge on the spread of drug-resistant Aspergillus spp. with the aim of defining optimal treatment strategies.

Deep amplicon sequencing reveals extensive allelic diversity in the erg11/CYP51 promoter and allows multi-population DMI fungicide resistance monitoring in the canola pathogen Leptosphaeria maculans

Continued use of fungicides provides a strong selection pressure towards strains with mutations to render these chemicals less effective. Previous research has shown that resistance to the demethylation inhibitor (DMI) fungicides, which target ergosterol synthesis, in the canola pathogen Leptosphaeria maculans has emerged in Australia and Europe. The change in fungicide sensitivity of individual isolates was found to be due to DNA insertions into the promoter of the erg11/CYP51 DMI target gene. Whether or not these were the only types of mutations and how prevalent they were in Australian populations was explored in the current study. New isolates with reduced DMI sensitivity were obtained from screens on DMI-treated plants, revealing eight independent insertions in the erg11 promoter. A novel deep amplicon sequencing approach applied to populations of ascospores fired from stubble identified an additional undetected insertion allele and quantified the frequencies of all known insertions, suggesting that, at least in the samples processed, the combined frequency of resistant alleles is between 0.0376% and 32.6%. Combined insertion allele frequencies positively correlated with population-level measures of in planta resistance to four different DMI treatments. Additionally, there was no evidence for erg11 coding mutations playing a role in conferring resistance in Australian populations. This research provides a key method for assessing fungicide resistance frequency in stubble-borne populations of plant pathogens and a baseline from which additional surveillance can be conducted in L. maculans. Whether or not the observed resistance allele frequencies are associated with loss of effective disease control in the field remains to be established.

Isolates of Colletotrichum truncatum with Resistance to Multiple Fungicides from Soybean in Northern Thailand

In Thailand, four systemic fungicides-carbendazim (Car), azoxystrobin (Azo), difenoconazole (Dif), and penthiopyrad (Pen)-are commonly used to control soybean anthracnose caused by Colletotrichum truncatum; however, the pathogen has developed resistance. From 2019 to 2020, fungicide resistance in C. truncatum from fields in Chiang Rai and Chiang Mai was monitored. In tests of 85 C. truncatum isolates for resistance to multiple fungicides, 15.3% were CarRAzoR, 34.1% were triple resistant (CarRAzoRDifR or CarRAzoRPenR), and 50.6% were CarRAzoRDifRPenR. Surprisingly, all isolates tested had lost their sensitivity to one or more of the fungicides tested. The carbendazim-resistant isolates carried a point mutation in the β-tubulin gene at codon 198 (E198A) or 200 (F200Y), and all azoxystrobin-resistant isolates had a mutation in the cytochrome b gene at codon 143 (G143A) or 129 (F129L). Moreover, a novel mutation at codon 208 (S208Y) in the gene encoding succinate dehydrogenase subunit B was detected in all of the isolates highly resistant to penthiopyrad. No mutation linked with difenoconazole resistance was detected in the genes encoding cytochrome P450 sterol 14α-demethylase. To the best of our knowledge, this is the first report of C. truncatum isolates resistant to multiple fungicides and serves as a warning to take measures to prevent the occurrence and distribution of these multiple-fungicide-resistant populations in soybean fields.

Dissipation Kinetics and Risk Assessment of Diniconazole, Dinotefuran, Metconazole, and Tebuconazole in Raphanus sativus L

This study investigated the degradation characteristics and conducted a risk assessment of four pesticides (Diniconazole, Dinotefuran, Metconazole, and Tebuconazole) in the leaves and roots of radish. Radish was cultivated in two greenhouse fields, and samples were collected at 0, 1, 2, 3, 5, 7, and 10 days after pesticide application. Sample analysis was performed using LC-MS/MS, and the recovery rates ranged from 70.1% to 118.6%. The biological half-life of Diniconazole was found to be 6.2 days (leaf and root), Dinotefuran was 5.3 days (leaf) and 4.6 days (root), Metconazole was 9.3 days (leaf) and 3.2 days (root), and Tebuconazole was 8.0 days (leaf) and 5.1 days (root). After comparing the maximum residue limits (MRL) of each pesticide in Korea with the residues during the pre-harvest interval (PHI), Diniconazole showed a Hazard quotient (HQ) exceeding 1, indicating potential risks for true consumers. Furthermore, Tebuconazole showed an HQ of 0.3 or higher, indicating a significant level of risk.

Effect of Streptomyces roseolus Cell-Free Supernatants on the Fungal Development, Transcriptome, and Aflatoxin B1 Production of Aspergillus flavus

Crop contamination by aflatoxin B1 (AFB1), an Aspergillus-flavus-produced toxin, is frequently observed in tropical and subtropical regions. This phenomenon is emerging in Europe, most likely as a result of climate change. Alternative methods, such as biocontrol agents (BCAs), are currently being developed to reduce the use of chemicals in the prevention of mycotoxin contamination. Actinobacteria are known to produce many bioactive compounds, and some of them can reduce in vitro AFB1 concentration. In this context, the present study aims to analyze the effect of a cell-free supernatant (CFS) from Streptomyces roseolus culture on the development of A. flavus, as well as on its transcriptome profile using microarray assay and its impact on AFB1 concentration. Results demonstrated that in vitro, the S. roseolus CFS reduced the dry weight and conidiation of A. flavus from 77% and 43%, respectively, and was therefore associated with a reduction in AFB1 concentration reduction to levels under the limit of quantification. The transcriptomic data analysis revealed that 5198 genes were differentially expressed in response to the CFS exposure and among them 5169 were downregulated including most of the genes involved in biosynthetic gene clusters. The aflatoxins' gene cluster was the most downregulated. Other gene clusters, such as the aspergillic acid, aspirochlorine, and ustiloxin B gene clusters, were also downregulated and associated with a variation in their concentration, confirmed by LC-HRMS.

Antifungal Activity of Hop Leaf Extracts and Xanthohumol on Two Strains of Venturia inaequalis with Different Sensitivities to Triazoles

Hop cones are well-known for their antimicrobial properties, attributed to their specialized metabolites. Thus, this study aimed to determine the in vitro antifungal activity of different hop parts, including by-products such as leaves and stems, and some metabolites against Venturia inaequalis, the causal agent of apple scab. For each plant part, two types of extracts, a crude hydro-ethanolic extract and a dichloromethane sub-extract, were tested on spore germination of two strains with different sensitivities to triazole fungicides. Both extracts of cones, leaves and stems were able to inhibit the two strains, whereas rhizomes did not show activity. The apolar sub-extract of leaves appeared as the most active modality tested with half maximal inhibitory concentrations (IC₅₀) of 5 and 10.5 mg·L^-1 on the sensitive strain and the strain with reduced sensitivity, respectively. Differences in activity level between strains were noticed for all active modalities tested. Sub-extracts of leaves were then separated into seven fractions by preparative HPLC and tested on V. inaequalis. One fraction, containing xanthohumol, was especially active on both strains. This prenylated chalcone was then purified by preparative HPLC and showed significant activity against both strains, with IC₅₀ of 1.6 and 5.1 mg·L^-1. Therefore, xanthohumol seems to be a promising compound to control V. inaequalis.

The triazole fungicide metconazole inhibits the homodimerization of human androgen receptors to suppress androgen-induced transcriptional activation

We assessed the mechanism of human androgen receptor-mediated endocrine-disrupting effect by a triazole fungicide, metconazole in this study. The internationally validated stably transfected transactivation (STTA) in vitro assay, which was established for determination of a human androgen receptor (AR) agonist/antagonist by using 22Rv1/MMTV_GR-KO cell line, alongside an in vitro reporter-gene assay to confirm AR homodimerization was used. The STTA in vitro assay results showed that metconazole is a true AR antagonist. Furthermore, the results from the in vitro reporter-gene assay and western blotting showed that metconazole blocks the nuclear transfer of cytoplasmic AR proteins by suppressing the homodimerization of AR. These results suggest that metconazole can be considered to have an AR-mediated endocrine-disrupting effect. Additionally, the evidence from this study might help identify the endocrine-disrupting mechanism of triazole fungicides containing a phenyl ring.

Design, Synthesis, In Vitro Antifungal Activity and Mechanism Study of the Novel 4-Substituted Mandelic Acid Derivatives

Plant diseases caused by phytopathogenic fungi are a serious threat in the process of crop production and cause large economic losses to global agriculture. To obtain high-antifungal-activity compounds with novel action mechanisms, a series of 4-substituted mandelic acid derivatives containing a 1,3,4-oxadiazole moiety were designed and synthesized. In vitro bioassay results revealed that some compounds exhibited excellent activity against the tested fungi. Among them, the EC₅₀ values of E₁₃ against Gibberella saubinetii (G. saubinetii), E₆ against Verticillium dahlia (V. dahlia), and E₁₈ against Sclerotinia sclerotiorum (S. sclerotiorum) were 20.4, 12.7, and 8.0 mg/L, respectively, which were highly superior to that of the commercialized fungicide mandipropamid. The morphological studies of G. saubinetii with a fluorescence microscope (FM) and scanning electron microscope (SEM) indicated that E₁₃ broke the surface of the hyphae and destroyed cell membrane integrity with increased concentration, thereby inhibiting fungal reproduction. Further cytoplasmic content leakage determination results showed a dramatic increase of the nucleic acid and protein concentrations in mycelia with E₁₃ treatment, which also indicated that the title compound E₁₃ could destroy cell membrane integrity and affect the growth of fungi. These results provide important information for further study of the mechanism of action of mandelic acid derivatives and their structural derivatization.

Synthesis, Antifungal Evaluation, 3D-QSAR, and Preliminarily Mechanism Study of Novel Chiral Mandelic Acid Derivatives

To investigate the effect of spatial configuration on the biological activity of the compounds, a series of chiral mandelic acid derivatives with a moiety of 1,3,4-oxadiazole thioether have been designed and synthesized. Bioassay results demonstrated that most title compounds with the S-configuration exhibited better in vitro antifungal activity against three plant fungi, such as H3' (EC₅₀ = 19.3 μg/mL) against Gibberella saubinetii, which was approximately 16 times higher than that of H3 (EC₅₀ = 317.0 μg/mL). CoMFA and CoMSIA models were established for 3D-QSAR analysis and provided an important support for further optimization of this series of compounds. Comparing the preliminary mechanism studies between enantiomers (H3 and H3') found that the S-configuration compound (H3') exhibited a stronger ability to destroy the surface structure of G. saubinetii mycelia, causing the leakage of intracellular substances to accelerate and the growth of the hyphae to be inhibited. The results provided a novel view for the further optimization of this series of active compounds and deep mechanism study of chiral pesticides.

Induced Expression of CYP51a and HK1 Genes Associated with Penconazole and Fludioxonil Resistance in the Potato Pathogen Fusarium oxysporum

Preventing antifungal resistance development and identifying pathogens with high, medium, and low risk of resistance development to a particular fungicide or fungicide class is crucial in the fight against phytopathogens. We characterized the sensitivity of potato wilt-associated Fusarium oxysporum isolates to fludioxonil and penconazole and assessed the effect of these fungicides on the expression of fungal sterol-14-α-demethylase (CYP51a) and histidine kinase (HK1) genes. Penconazole stunted the growth of F. oxysporum strains at all concentrations used. While all isolates were susceptible to this fungicide, concentrations of up to 1.0 μg/mL were insufficient to cause a 50% inhibition. At low concentrations (0.63 and 1.25 μg/mL), fludioxonil stimulated growth in F. oxysporum. With an increase in the concentration of fludioxonil, only one strain (F. oxysporum S95) exhibited moderate sensitivity to the fungicide. Interaction of F. oxysporum with penconazole and fludioxonil leads to respective elevated expressions of the CYP51a and HK1 genes, which upsurge with increasing concentration of the fungicides. The data obtained indicate that fludioxonil may no longer be suitable for potato protection and its continuous use could only lead to an increased resistance with time.

Oral Exposure to Epoxiconazole Disturbed the Gut Micro-Environment and Metabolic Profiling in Male Mice

Epoxiconazole (EPX), a triazole fungicide, is widely used in agriculture to control pests and diseases. High residual and occupational exposure to EPX increases health risks, and evidence of potential harm to mammals remains to be added. In the present study, 6-week-old male mice were exposed to 10 and 50 mg/kg bw EPX for 28 days. The results showed that EPX significantly increased the liver weights. EPX also decreased the mucus secretion of the colon and altered intestinal barrier function in mice including a reduced expression of some genes (Muc2, meprinβ, tjp1). Moreover, EPX altered the composition and abundance of gut microbiota in the colon of mice. The alpha diversity indices (Shannon, Simpson) in the gut microbiota increased after exposure to EPX for 28 days. Interestingly, EPX increased the ratio of Firmicutes to Bacteroides and the abundance of other harmful bacteria including Helicobacter and Alistipes. Based on the untargeted metabolomic analysis, it was found that EPX altered the metabolic profiles of the liver in mice. KEGG analysis of differential metabolites revealed that EPX disrupted the pathway related to glycolipid metabolism, and the mRNA levels of related genes were also confirmed. In addition, the correlation analysis showed that the most altered harmful bacteria were associated with some significantly altered metabolites. The findings highlight that EPX exposure changed the micro-environment and lipid metabolism disturbance. These results also suggest that the potential toxicity of triazole fungicides to mammals cannot be ignored.

Targeted deletion of three CYP51s in Fusarium fujikuroi and their different roles in determining sensitivity to 14α-demethylase inhibitor fungicides

BACKGROUND

Fusarium fujikuroi is the pathogenic agent of rice bakanae disease and has developed serious resistance to prochloraz, a 14α-demethylase inhibitor (DMI). Prochloraz resistance in F. fujikuroi is caused by cooperation between FfCyp51B with Cyp51A and shows cross-resistance only to prothioconazole but not to tebuconazole, difenoconazole, propiconazole, metconazole, hexaconazole, and triadimefon. This study aimed to analyze the functions of the three Cyp51s in F. fujikuroi, especially their role in determining sensitivity to DMIs.

RESULTS

The respective deletion of FfCyp51A, Cyp51B, and Cyp51C had no obvious effect on morphology, conidium germination, or pathogenicity. The involvement of growth, growth and ergosterol biosynthesis, and conidium production and ergosterol biosynthesis was observed for FfCyp51A, Cyp51B, and Cyp51C, respectively. Compared with the sensitive isolate of F. fujikuroi, the effect on sensitivity to the tested DMIs was divided into four groups: (i) both of Cyp51A and Cyp51B positively regulate the sensitivity to prochloraz and prothioconazole; (ii) Cyp51B positively regulate the sensitivity to tebuconazole and metconazole, but negatively regulate the sensitivity to difenoconazole; (iii) Cyp51A and Cyp51B play opposite roles in the sensitivity to triadimefon. Therefore, deletion of Cyp51A in F. fujikuroi confers a higher sensitivity to triadimefon, while deletion of Cyp51B results in a triadimefon-resistant mutant isolate; (iv) deletion of Cyp51B yielded a mutant isolate that was more resistant to propiconazole and hexaconazole.

CONCLUSION

Sophisticated interactions exist within the three Cyp51 genes to DMIs fungicides sensitivity in F. fujikuroi, and Cyp51B probably plays a more critical role than Cyp51A and Cyp51C. © 2022 Society of Chemical Industry.

Improvement of Akanthomyces lecanii resistance to tebuconazole through UV-C radiation and selective pressure on microbial evolution and growth arenas

Tebuconazole (TEB) is a fungicide widely used in agriculture; however, its constant application has increased the emergence of resistant plant pathogenic fungal strains and reduced the effectiveness of fungi as biological control agents; for instance, the entomopathogenic and hyperparasitic fungus Akanthomyces lecanii, suitable for simultaneous biological control of insect pest and plant pathogenic fungi, is highly sensitive to fungicides. We carried out the induction of resistance to TEB in two wild type strains of A. lecanii by UV radiation and selective pressure in increasing fungicide gradients using a modified Microbial Evolution and Growth Arena (MEGA), to produce A. lecanii strains that can be used as biological control agent in the presence of tebuconazole. Nine UV-induced and three naturally adapted A. lecanii strains were resistant to TEB at the agriculturally recommended dose, and three irradiated strains were resistant to TEB concentration ten times higher; moreover, growth, sporulation rates, production of hydrolytic enzymes, and virulence against the hemipteran Coccus viridis, a major pest of coffee crops, were not affected in the TEB-resistant strains. These A. lecanii TEB-resistant strains would have a greater opportunity to develop and to establish themselves in fields where the fungicide is present and can be used in a combined biological-chemical strategy to improve insect and plant pathogenic fungal control in agriculture. Also, the selective pressure through modified MEGA plate methodology can be used for the adaptation of entomopathogenic filamentous fungi to withstand other chemical or abiotic stresses that limits its effectiveness for pest control.

Metabolomics-Based Mechanistic Insights into Revealing the Adverse Effects of Pesticides on Plants: An Interactive Review

In plant biology, metabolomics is often used to quantitatively assess small molecules, metabolites, and their intermediates in plants. Metabolomics has frequently been applied to detect metabolic alterations in plants exposed to various biotic and abiotic stresses, including pesticides. The widespread use of pesticides and agrochemicals in intensive crop production systems is a serious threat to the functionality and sustainability of agroecosystems. Pesticide accumulation in soil may disrupt soil-plant relationships, thereby posing a pollution risk to agricultural output. Application of metabolomic techniques in the assessment of the biological consequences of pesticides at the molecular level has emerged as a crucial technique in exposome investigations. State-of-the-art metabolomic approaches such as GC-MS, LC-MS/MS UHPLC, UPLC-IMS-QToF, GC/EI/MS, MALDI-TOF MS, and ¹H-HR-MAS NMR, etc., investigating the harmful effects of agricultural pesticides have been reviewed. This updated review seeks to outline the key uses of metabolomics related to the evaluation of the toxicological impacts of pesticides on agronomically important crops in exposome assays as well as bench-scale studies. Overall, this review describes the potential uses of metabolomics as a method for evaluating the safety of agricultural chemicals for regulatory applications. Additionally, the most recent developments in metabolomic tools applied to pesticide toxicology and also the difficulties in utilizing this approach are discussed.

Novel (Z)/(E)-1,2,4-triazole derivatives containing oxime ether moiety as potential ergosterol biosynthesis inhibitors: design, preparation, antifungal evaluation, and molecular docking

Inspired by the highly effective and broad-spectrum antifungal activity of ergosterol biosynthesis inhibitions, a series of novel 1,2,4-triazole derivatives containing oxime ether moiety were constructed for screening the bioactivity against phytopathogenic fungi. The (Z)- and (E)-isomers of target compounds were successfully separated and identified by the spectroscopy and single crystal X-ray diffraction analyses. The bioassay results showed that the (Z)-isomers of target compounds possessed higher antifungal activity than the (E)-isomers. Strikingly, the compound (Z)-5o exhibited excellent antifungal activity against Rhizoctonia solani with the EC₅₀ value of 0.41 μg/mL in vitro and preventive effect of 94.58% in vivo at 200 μg/mL, which was comparable to the positive control tebuconazole. The scanning electron microscopy observation indicated that the compound (Z)-5o caused the mycelial morphology to become wizened and wrinkled. The molecular docking modes of (Z)-5o and (E)-5o with the potential target protein RsCYP51 were especially compared. And the main interactions between ligands and amino acid residues were carefully analyzed to preliminarily explain the mechanism leading to the difference of activity between two isomers. The study provided a new lead molecular skeleton for developing novel triazole fungicides targeting ergosterol biosynthesis.

4-Allyl-2-methoxyphenol modulates the expression of genes involved in efflux pump, biofilm formation and sterol biosynthesis in azole resistant Aspergillus fumigatus

Introduction

Antifungal therapy for aspergillosis is becoming problematic because of the toxicity of currently available drugs, biofilm formation on host surface, and increasing prevalence of azole resistance in Aspergillus fumigatus. Plants are rich source of bioactive molecules and antimicrobial activity of aromatic bioactive compounds draws attention because of its promising biological properties. The present study elucidated the antibiofilm activity of 4-allyl-2-methoxyphenol (eugenol) against azole-resistant environmental A. fumigatus isolates.

Methods

Soil samples were collected from agricultural fields across India; azole-resistant A. fumigatus (ARAF) were isolated followed by their molecular identification. Antibiofilm activity of eugenol was calculated via tetrazolium based-MTT assay. The expression of the multidrug efflux pumps genes MDR1, MDR4, transporters of the MFS gene, erg11A gene encoding 14α demethylase, and transcription regulatory genes, MedA, SomA and SrbA, involved in biofilm formation of A. fumigatus were calculated by quantitative real time PCR.

Results

Out of 89 A. fumigatus isolates, 10 were identified as azole resistant. Eugenol exhibited antibiofilm activity against ARAF isolates, ranging from 312 to 500 µg/mL. Confocal laser scanning microscopy analysis revealed absence of extracellular matrix of ARAF biofilm after eugenol treatment. The gene expression indicated significantly low expression of efflux pumps genes MDR1, MDR4, erg11A and MedA in eugenol treated ARAF isolates when compared with untreated isolates.

Conclusions

Our results demonstrate that eugenol effects the expression of efflux pump and biofilm associated genes as well as inhibits biofilm formation in azole resistant isolates of A. fumigatus.

Synergistic effect of amino acid substitutions in CYP51B for prochloraz resistance in Fusarium fujikuroi

Prochloraz has been used to control Fusarium fujikuroi, the causative pathogen of rice bakanae disease. Linkage analysis of FfCYP51 genes in the progenies obtained from crossing prochloraz moderately resistant and sensitive strains suggested that the FfCYP51B gene is involved in prochloraz resistance. Sequence comparison revealed that the prochloraz-resistant strain had an F511S or S312T/F511S substitution in FfCYP51B compared with the sensitive strains. The contribution of the S312T and F511S substitutions in FfCYP51B to prochloraz resistance was investigated by creating S/F-, T/F-, or T/S- types at 312/511 codons from the S/S-type, which is a natural moderately resistant strain, using a gene-editing technique. T/S exhibited the highest prochloraz resistance, followed by S/S-, T/F-, and S/F-types. These results indicated that the S312T and F511S substitutions in FfCYP51B had a synergistic effect on prochloraz resistance in F. fujikuroi.

Antifungal metabolites, their novel sources, and targets to combat drug resistance

Excessive antibiotic prescriptions as well as their misuse in agriculture are the main causes of antimicrobial resistance which poses a growing threat to public health. It necessitates the search for novel chemicals to combat drug resistance. Since ancient times, naturally occurring medicines have been employed and the enormous variety of bioactive chemicals found in nature has long served as an inspiration for researchers looking for possible therapeutics. Secondary metabolites from microorganisms, particularly those from actinomycetes, have made it incredibly easy to find new molecules. Different actinomycetes species account for more than 70% of naturally generated antibiotics currently used in medicine, and they also produce a variety of secondary metabolites, including pigments, enzymes, and anti-inflammatory compounds. They continue to be a crucial source of fresh chemical diversity and a crucial component of drug discovery. This review summarizes some uncommon sources of antifungal metabolites and highlights the importance of further research on these unusual habitats as a source of novel antimicrobial molecules.

The fungicide prothioconazole and its metabolite prothioconazole-desthio disturbed the liver-gut axis in mice

The triazole fungicide prothioconazole (PTC) can cause adverse effects in animals, and its main metabolite prothioconazole-desthio (PTC-d) is even much more harmful. However, the toxic effects of PTC and PTC-d on the liver-gut axis of mice are still unknown. In the present experiment, we found that oral exposure to PTC and PTC-d increased total bile acids (TBAs) levels in the serum, liver, and feces. Correspondingly, the transcription of genes involved in bile acids (BAs) disposition was significantly influenced by PTC or PTC-d exposure. Furthermore, the BAs composition of serum BAs was analyzed by LC-MS, and the results indicated that PTC and PTC-d exposure changed the BAs composition, lowered the ratio of conjugated/unconjugated BAs, elevated the ratio of CA/b-MCA, and enhanced the hydrophobicity of BAs pool. 16s RNA gene sequencing of the DNA from colonic contents uncovered that PTC and PTC-d exposure altered the relative abundance and constitution of intestinal microbiota, increasing the relative level of Lactobacillus with bile salt hydrolase (BSH) activity. Furthermore, PTC and PTC-d exposure impaired the gut barrier function, causing an increase in mucus secretion. In particular, the effects of PTC-d on some endpoints in the BAs metabolism and gut barrier function had been proven to be more significant than the parent compound PTC. All these findings draw attention to the health risk of PTC and PTC-d exposure in regulating BAs metabolism, which might lead to some metabolic disorders and occur of related diseases in animals.

Microbial Contamination in the Coffee Industry: An Occupational Menace besides a Food Safety Concern?

Respiratory abnormalities among workers at coffee roasting and packaging facilities have already been reported; however, little is known about microbiological contamination inside coffee production facilities. This study intends to assess the microbial contamination (fungi and bacteria) in two coffee industries from Brazil with a multi-approach protocol for sampling and for subsequent analyses using four main sources of samples: filtering respiratory protection devices (FRPD) used by workers, settled dust, electrostatic dust cloths (EDC) and coffee beans. The fungal contamination in the assessed industries was also characterized through the molecular detection of toxigenic species and antifungal resistance. Total bacteria contamination presented the highest values in FRPD collected from both industries (7.45 × 104 CFU·m-2; 1.09 × 104 CFU·m-2). Aspergillus genera was widespread in all the environmental samples collected and sections with clinical relevance (Fumigati) and with toxigenic potential (Nigri and Circumdati) were recovered from FRPD. Circumdati section was observed in 4 mg/mL itraconazole. Sections Circumdati (EDC, coffee beans and settled dust) and Nidulantes (EDC, coffee beans and FRPD) were detected by qPCR. Some of the targeted Aspergillus sections that have been identified microscopically were not detected by qPCR and vice-versa. Overall, this study revealed that microbial contamination is a potential occupational risk in the milling stage and should be tackled when assessing exposure and performing risk assessment. In addition, a multi-sampling campaign should be the approach to follow when assessing microbial contamination and FRPD should be included in this campaign. Occupational exposure to mycotoxins should be considered due to high fungal diversity and contamination. A One Health approach should address these issues in order to prevent consumption of coffee crops and beans infected by fungi and, more specifically, to avoid widespread azole resistance.

Analysis of pesticide and persistent organic pollutant residues in German bats

Bats are strictly protected throughout Europe. They are a highly diverse order of mammals in terms of body size, body weight, migratory behaviour, trophic niche specialisation and habitat use. The latter ranges from urban areas and arable land to forest. Due to their low reproductive rate, environmental stressors can have a major impact on bat populations. Pesticides in particular are discussed as an important driver of bat population declines. In this work, we analysed nearly 400 animals of five different species (Eptesicus serotinus, Myotis myotis, Nyctalus noctula, Pipistrellus pipistrellus, and Plecotus auritus) from all over Germany for residues of 209 pesticides and persistent organic pollutants. Residue analysis was conducted with a previously developed method using a miniaturized quick, easy, cheap, effective, rugged and safe (QuEChERS) sample preparation and gas chromatography-tandem mass spectrometry for separation and detection. These analytical data were statistically correlated with the known data on the animals (e.g. age, sex, place and time of finding). Of 209 pesticides and pollutants investigated, 28 compounds were detected, the most frequent being organochlorine insecticides and polychlorinated biphenyls, which have been banned for decades by the Stockholm Convention on Persistent Organic Pollutants. Detection of more recent pesticides that were legally used for the last decade included azole antifungals and the insecticide fipronil. The bats contained between four and 25 different residues. Statistical data analyses showed that the distribution throughout Germany is largely comparable, and single exceptions were observed in specialized ecological niches. In conclusion, this work provides the largest dataset of pesticide and persistent organic pollutant residues in European bats to date.

Rhamnolipids and fengycins, very promising amphiphilic antifungal compounds from bacteria secretomes, act on Sclerotiniaceae fungi through different mechanisms

Rhamnolipids (RLs) and fengycins (FGs) are amphiphilic lipid compounds from bacteria secretomes proposed to replace synthetic pesticides for crop protection. They both display plant defense triggering properties and direct antimicrobial activities. In particular, they have well reported antifungal effects against phytopathogenic fungi. RLs and FGs are considered to act through a direct interaction with membrane lipids and a destabilization of microorganism plasma membrane, thereby limiting the risk of resistance emergence. The main objective of this work was to gain insights in the antimycelial mode of action of these metabolites to promote them as environment and human health friendly biocontrol solutions. Their biocidal effects were studied on two Sclerotiniaceae fungi responsible for diseases in numerous plant species worldwide. We show here that different strains of Botrytis cinerea and Sclerotinia sclerotiorum have opposite sensitivities to RLs and FGs on plate experiments. Overall, B. cinerea is more sensitive to FGs while S. sclerotiorum is more sensitive to RLs. Electron microscopy observations demonstrated that RLs induce mycelial destructuring by asperities emergence and hyphal fusions whereas FGs promote swelling and formation of vesicle-like structures due to vacuole fusions and autophagy. Permeability studies, phosphatidylserine externalization and reactive oxygen species production assessments showed a programmed cell death triggering by RLs at medium concentrations (until 50 μg mL⁻¹) and necrosis characteristics at higher concentration. Programmed cell death was always observed on hyphae treated with FGs. Quantifications of mycelial ergosterol content indicated that a higher ergosterol rate in S. sclerotiorum correlates with increasing sensitivity to RLs. Oppositely, a lower ergosterol rate in B. cinerea correlates with increasing sensitivity to FGs, which was confirmed by ergosterol biosynthesis inhibition with tebuconazole. This gain of knowledge will help to better understand the mode of action of RLs and FGs to fight specific plant fungal diseases.

Emerging Fungal Infections: from the Fields to the Clinic, Resistant Aspergillus fumigatus and Dermatophyte Species: a One Health Perspective on an Urgent Public Health Problem

Purpose of Review

For this review, we use a One Health approach to examine two globally emerging public health threats related to antifungal drug resistance: triazole-resistant Aspergillus fumigatus infections, which can cause a life-threatening illness in immunocompromised hosts, and antifungal-resistant dermatophytosis, which is an aggressive skin infection caused by dermatophyte molds. We describe the state of current scientific knowledge and outline necessary public health actions to address each issue.

Recent Findings

Recent evidence has identified the agricultural use of triazole fungicides as an important driver of triazole-resistant A. fumigatus infections. Antifungal-resistant dermatophyte infections are likely driven by the inappropriate use of antifungal drugs and antibacterial and corticosteroid creams.

Summary

This review highlights the need for a One Health approach to address emerging antifungal resistant infections, emphasizing judicious antifungal use to preserve available treatments; strengthened laboratory capacity to identify antifungal resistance; and improved human, animal, and environmental surveillance to detect emerging resistance, monitor trends, and evaluate the effectiveness of efforts to decrease spread.

Bioactivity of mefentrifluconazole against different Fusarium spp

Emergence and development of resistance to 14α-demethylase inhibitors (DMIs) have become a critical issue in both agriculture and medical fields. Mefentrifluconazole, the first isopropanol triazole fungicide belonging to a new subclass of DMIs, has been proposed to show high activity, minimal adverse side effects, and inconsistent cross resistance with other DMIs due to its high structural flexibility. In this study, mefentrifluconazole showed disparate inhibitory activity against the mycelium growth of seven tested Fusarium species. The most sensitive species included F. oxysporum, F. proliferatum, F. commuae, and F. fujikuroi, followed by F. equiseti and F. graminearum, while F. solani was most insensitive. Consistently, mefentrifluconazole presented the strongest inhibiting effects on conidium germination, cell membrane integrity, and ergosterol biosynthesis in F. fujikuroi, followed by F. graminearum, while F. solani ranked last. Further results indicated that all F. fujikuroi isolates causing rice bakanae disease (RBD) were sensitive to mefentrifluconazole regardless of their resistance to prochloraz, tebuconazole, carbendazim, and phenamacril. Additionally, the inoculation tests found that mefentrifluconazole presented a better protective efficacy on rice seedlings when applied 12 h before the F. fujikuroi inoculation, compared to applied 12 h post the inoculation. Overall, this study demonstrated the various bioactivity of mefentrifluconazole combating Fusarium spp. and put new insights into RBD management as well as the applications of DMIs.

Synthesis, Antifungal Activity, Cytotoxicity and QSAR Study of Camphor Derivatives

Control of fungal phytopathogens affecting crops and woodlands is an important goal in environmental management and the maintenance of food security. This work describes the synthesis of 37 camphor derivatives, of which 27 were new compounds. Their antifungal effects on six fungi were evaluated in vitro. Compounds 3a, 4a and 5k showed strong antifungal activity against Trametes versicolor, with EC₅₀ values of 0.43, 6.80 and 4.86 mg/L, respectively, which were better than that of tricyclazole (EC₅₀ 118.20 mg/L) and close to or better than that of carbendazim (EC₅₀ 1.20 mg/L). The most potent compound, 3a, exhibited broad-spectrum antifungal activity towards six fungi with EC₅₀ values within the range of 0.43–40.18 mg/L. Scanning electron microscopy demonstrated that compounds 3a, 4a and 5k gave irregular growth and shriveling of the mycelia. In vitro cytotoxicity evaluation revealed that the tested camphor derivatives had mild or no cytotoxicity for LO₂ and HEK293T cell lines. Quantitative structure−activity relationship (QSAR) analysis revealed that the number of F atoms, relative molecular weight, the atomic orbital electronic population and total charge on the positively charged surfaces of the molecules of camphor derivatives have effects on antifungal activity. The present study may provide a theoretical basis for a high-value use of camphor and could be helpful for the development of novel potential antifungals.