Triazole Priming as an Adaptive Response and Gateway to Resistance in Aspergillus fumigatus

Priming enhances tolerance of Fusarium graminearum to triazole

Organisms exposed to environmental stimuli can develop "memory" of those experiences, a phenomenon known as priming, which allows them to better adapt to subsequent stimuli. Growing evidence has shown that fungi can "remember" past encounters, but the priming effect remains poorly understood in phytopathogenic fungi. In this study, we examined the priming effect in Fusarium graminearum, the causative agent of Fusarium head blight (FHB), by culturing its conidia in the presence of a median effective concentration (EC50) of triazole fungicide. We observed that primed conidia exhibited significantly higher germination rates and longer hyphal length than unprimed conidia when exposed to double EC50 concentration of triazole. The triazole priming effect in F. graminearum was retained in conidia for an extended period but was not stably heritable. Further investigations revealed that this priming effect was linked to increased over-expression of the fungicide target genes (FgCYP51s) above the level seen in non-primed F. graminearum. This study reveals that F. graminearum develops adaptive resistance following treatment with triazole fungicides, and elucidates the mechanism behind priming, which is regulated by the transcription factor FgSR. This regulation leads to the upregulation of FgCYP51 expression, thereby mediating the observed adaptive resistance. This provides a theoretical basis for understanding the development of resistance in pathogens and offers relevant guidance for the use of triazole fungicides in the control of FHB.

In vitro and silico activity of piperlongumine against azole-susceptible/resistant Aspergillus fumigatus and terbinafine-susceptible/resistant Trichophyton species

In recent years, the widespread emergence of drug resistance in yeasts and filamentous fungi to existing antifungal armamentariums has become a severe threat to global health. There is also concern regarding increased rates of azole resistance in Aspergillus fumigatus and Terbinafine resistance in Trichophyton species. To overcome this concern of resistance to regular therapies, new antifungal drugs with novel and effective mechanisms are crucially needed. Herbal remedies may be promising strategies for the treatment of resistant infections. We aimed to investigate the in vitro and silico activity of piperlongumine against clinical azole susceptible/resistant A. fumigatus and terbinafine-susceptible/resistant Trichophyton species. In the current study, piperlongumine demonstrated potent antifungal activity, with minimum inhibitory concentrations (MICs) ranging from 0.016-4 μg/mL against Trichophyton isolates and 0.25-2 μg/mL for A. fumigatus isolates. Additionally, molecular docking studies indicated that piperlongumine has a strong binding affinity to the active sites of squalene epoxidase and sterol 14-alpha demethylase. However, further studies are warranted to correlate these findings with clinical outcomes and provide the basis for further investigations to pave the way for developing novel antifungal agents.

Antimicrobial resistance in the wild: Insights from epigenetics

Spreading of bacterial and fungal strains that are resistant to antimicrobials poses a serious threat to the well-being of humans, animals, and plants. Antimicrobial resistance has been mainly investigated in clinical settings. However, throughout their evolutionary history microorganisms in the wild have encountered antimicrobial substances, forcing them to evolve strategies to combat antimicrobial action. It is well known that many of these strategies are based on genetic mechanisms, but these do not fully explain important aspects of the antimicrobial response such as the rapid development of resistance, reversible phenotypes, and hetero-resistance. Consequently, attention has turned toward epigenetic pathways that may offer additional insights into antimicrobial mechanisms. The aim of this review is to explore the epigenetic mechanisms that confer antimicrobial resistance, focusing on those that might be relevant for resistance in the wild. First, we examine the presence of antimicrobials in natural settings. Then we describe the documented epigenetic mechanisms in bacteria and fungi associated with antimicrobial resistance and discuss innovative epigenetic editing techniques to establish causality in this context. Finally, we discuss the relevance of these epigenetic mechanisms on the evolutionary dynamics of antimicrobial resistance in the wild, emphasizing the critical role of priming in the adaptation process. We underscore the necessity of incorporating non-genetic mechanisms into our understanding of antimicrobial resistance evolution. These mechanisms offer invaluable insights into the dynamics of antimicrobial adaptation within natural ecosystems.

Triazole resistance in Aspergillus fumigatus exposed to new chiral fungicide mefentrifluconazole

BACKGROUND

Triazole resistance in the human fungal pathogen Aspergillus fumigatus has been a growing challenge in clinic treatment with triazole drugs such as itraconazole. The fast evolvement of triazole resistance in A. fumigatus in the ecosystem has drawn great attention, and there has been a possible link between the application of triazole fungicides in agriculture and triazole resistance in A. fumigatus. The change in susceptibility of A. fumigatus exposed to the new chiral triazole fungicide mefentrifluconazole was investigated in this study.

RESULTS

The results indicated that triazole resistance in A. fumigatus was acquired with exposure to mefentrifluconazole at a level of greater than or equal to 2 mg L^-1 in liquid medium and soil (not at 0.4 nor 1 mg L^-1 ). Interestingly, stereoselectivity was found in the acquisition of triazole resistance in A. fumigatus when exposed to mefentrifluconazole. R-mefentrifluconazole, which is very active on plant pathogens, exhibited stronger possibility in the development of the resistance in A. fumigatus than its antipode. Overexpression of cyp51A, AtrF, AfuMDR1 and AfuMDR4 were associated with the acquired resistance in A. fumigatus with hereditary stability.

CONCLUSION

The results suggest that triazole resistance in A. fumigatus could be resulted from the selection of mefentrifluconazole at concentrations larger than 2 mg L^-1 . Mefentrifluconazole should be applied within the dosage recommended by good agricultural practice to avoid the resistance in A. fumigatus in soil. This also may be applicable to other triazole fungicides. © 2022 Society of Chemical Industry.