Antimicrobial resistance is a global issue that threatens the effective practice of modern medicine and global health. The emergence of multidrug-resistant (MDR) fungal strains of Candida auris and azole-resistant Aspergillus fumigatus were highlighted in the Centers for Disease Control and Prevention’s (CDC) 2019 report, Antibiotic Resistance Threats in the United States. Conventional antifungals used to treat fungal infections are no longer as effective, leading to increased mortality. Compounding this issue, there are very few new antifungals currently in development. Plants from traditional medicine represent one possible research path to addressing the issue of MDR fungal pathogens. In this commentary piece, we discuss how medical ethnobotany—the study of how people use plants in medicine—can be used as a guide to identify plant species for the discovery and development of novel antifungal therapies.

The structural determination of natural products (NPs) can be arduous because of sample heterogeneity. This often demands iterative purification processes and characterization of complex molecules that may be available only in miniscule quantities. Microcrystal electron diffraction (microED) has recently shown promise as a method to solve crystal structures of NPs from nanogram quantities of analyte. However, its implementation in NP discovery remains hampered by sample throughput and purity requirements, akin to traditional NP-discovery workflows. In the methods described herein, we leverage the resolving power of transmission electron microscopy (TEM) and the miniaturization capabilities of deoxyribonucleic acid (DNA) microarray technology to address these challenges through the establishment of an NP screening platform, array electron diffraction (ArrayED). In this workflow, an array of high-performance liquid chromatography (HPLC) fractions taken from crude extracts was deposited onto TEM grids in picoliter-sized droplets. This multiplexing of analytes on TEM grids enables 1200 or more unique samples to be simultaneously inserted into a TEM instrument equipped with an autoloader. Selected area electron diffraction analysis of these microarrayed grids allows for the rapid identification of crystalline metabolites. In this study, ArrayED enabled structural characterization of 14 natural products, including four novel crystal structures and two novel polymorphs, from 20 crude extracts. Moreover, we identify several chemical species that would not be detected by standard mass spectrometry (MS) or ultraviolet-visible (UV/vis) spectroscopy and crystal forms that would not be characterized using traditional methods.

Among fungal pathogens, infections by drug-resistant Candida species continue to pose a major challenge to healthcare. This study aimed to evaluate the activity of the bioactive natural product, penta-O-galloyl-β-d-glucose (PGG) against multidrug-resistant (MDR) Candida albicans, MDR Candida auris, and other MDR non-albicans Candida species. Here, we show that PGG has a minimum inhibitory concentration (MIC) of 0.25-8 μg mL^-1 (0.265-8.5 μM) against three clinical strains of C. auris and a MIC of 0.25-4 μg mL^-1 (0.265-4.25 μM) against a panel of other MDR Candida species. Our cytotoxicity studies found that PGG was well tolerated by human kidney, liver, and epithelial cells with an IC₅₀ > 256 μg mL^-1 (>272 μM). We also show that PGG is a high-capacity iron chelator and that deletion of key iron homeostasis genes in C. albicans rendered strains hypersensitive to PGG. In conclusion, PGG displayed potent anti-Candida activity with minimal cytotoxicity for human cells. We also found that the antifungal activity of PGG is mediated through an iron-chelating mechanism, suggesting that the compound could prove useful as a topical treatment for superficial Candida infections.

This study highlights the potential of Punica granatum (pomegranate) peel extract (PPE) as a natural antimicrobial alternative to synthetic chemicals. Pomegranate peels, typically considered a byproduct of fruit processing, contain bioactive compounds such as polyphenols, flavonoids, and tannins. This research explored the antimicrobial efficacy of these phytochemicals against Staphylococcus aureus using a bioassay-guided fractionation approach to identify key bioactive components. While evaluating antimicrobial efficacy is critical, it is equally important to ensure safety for human use. Therefore, we assessed the cytotoxicity of punicalagins α and β on human keratinocytes to determine their biocompatibility and potential for safe application in food or therapeutic settings. The antibacterial activity of PPE was then evaluated using different food models. Punicalagins α and β were identified as individual compounds, and their pure reference forms showed a minimum inhibitory concentration (MIC) of 16 μg/mL. None of the tested fractions exhibited significant cytotoxicity to human keratinocytes (HaCaTs) (IC₅₀ > 128 μg/mL). A significant reduction of up to 0.8-fold in bacterial cell counts was observed after PPE incorporation into tested food models. This research underscores the importance of exploring sustainable antimicrobial solutions derived from food industry byproducts as alternatives to synthetic antibiotics.