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Although polyenes were the first broad spectrum antifungal drugs on the market, after 70 years they are still the gold standard to treat a variety of fungal infections. Polyenes such as amphotericin B have a controversial image. They are the antifungal drug class with the broadest spectrum, resistance development is still relatively rare and fungicidal properties are extensive. Yet, they come with a significant host toxicity that limits their use. Relatively recently, the mode of action of polyenes has been revised, new mechanisms of drug resistance were discovered and emergent polyene resistant species such as Candida auris entered the picture. This review provides a short description of the history and clinical use of polyenes, and focusses on the ongoing debate concerning their mode of action, the diversity of resistance mechanisms discovered to date and the most recent trends in polyene resistance development.

Candida auris is a recently discovered human fungal pathogen and has shown an alarming potential for developing multi- and pan-resistance toward all classes of antifungals most commonly used in the clinic. Currently, C. auris has been globally recognized as a nosocomial pathogen of high concern due to this evolutionary potential. Candida auris is globally recognized as an opportunistic fungal pathogen of high concern, due to its extensive multidrug resistance (MDR). Still, molecular mechanisms of MDR are largely unexplored. This is the first account of genome-wide evolution of MDR in C. auris obtained through serial in vitro exposure to azoles, polyenes, and echinocandins. We show the stepwise accumulation of copy number variations and novel mutations in genes both known and unknown in antifungal drug resistance. Echinocandin resistance was accompanied by a codon deletion in FKS1 hot spot 1 and a substitution in FKS1 “novel” hot spot 3. Mutations in ERG3 and CIS2 further increased the echinocandin MIC. Decreased azole susceptibility was linked to a mutation in transcription factor TAC1b and overexpression of the drug efflux pump Cdr1, a segmental duplication of chromosome 1 containing ERG11 , and a whole chromosome 5 duplication, which contains TAC1b . The latter was associated with increased expression of ERG11 , TAC1b , and CDR2 but not CDR1 . The simultaneous emergence of nonsense mutations in ERG3 and ERG11 was shown to decrease amphotericin B susceptibility, accompanied with fluconazole cross-resistance. A mutation in MEC3 , a gene mainly known for its role in DNA damage homeostasis, further increased the polyene MIC. Overall, this study shows the alarming potential for and diversity of MDR development in C. auris , even in a clade until now not associated with MDR (clade II), stressing its clinical importance and the urge for future research. IMPORTANCE Candida auris is a recently discovered human fungal pathogen and has shown an alarming potential for developing multi- and pan-resistance toward all classes of antifungals most commonly used in the clinic. Currently, C. auris has been globally recognized as a nosocomial pathogen of high concern due to this evolutionary potential. So far, this is the first study in which the stepwise progression of multidrug resistance (MDR) in C. auris is monitored in vitro . Multiple novel mutations in known resistance genes and genes previously not or vaguely associated with drug resistance reveal rapid MDR evolution in a C. auris clade II isolate. Additionally, this study shows that in vitro experimental evolution can be a powerful tool to discover new drug resistance mechanisms, although it has its limitations.

Candida auris is an emerging nosocomial fungal pathogen associated with life-threatening invasive disease due to its persistent colonization, high level of transmissibility and multi-drug resistance. Aggregative and non-aggregative growth phenotypes for C. auris strains with different biofilm forming abilities, drug susceptibilities and virulence characteristics have been described. Using comprehensive transcriptional analysis we identified key cell surface adhesins that were highly upregulated in the aggregative phenotype during in vitro and in vivo grown biofilms using a mouse model of catheter infection. Phenotypic and functional evaluations of generated null mutants demonstrated crucial roles for the adhesins Als4112 and Scf1 in mediating cell-cell adherence, coaggregation and biofilm formation. While individual mutants were largely non-aggregative, in combination cells were able to co-adhere and aggregate, as directly demonstrated by measuring cell adhesion forces using single-cell atomic force spectroscopy. This co-adherence indicates their role as complementary adhesins, which despite their limited similarity, may function redundantly to promote cell-cell interaction and biofilm formation. Functional diversity of cell wall proteins may be a form of regulation that provides the aggregative phenotype of C. auris with flexibility and rapid adaptation to the environment, potentially impacting persistence and virulence. Here, Wang et al show that Candida auris cell wall adhesins function redundantly to promote cell-cell interaction and biofilm formation as a form of regulation and potential adaption to the environment.

Background Humans impose a significant pressure on large herbivore populations, such as hippopotami, through hunting, poaching, and habitat destruction. Anthropogenic pressures can also occur indirectly, such as artificial lake creation and the subsequent introduction of invasive species that alter the ecosystem. These events can lead to drastic changes in parasite diversity and transmission, but generally receive little scientific attention. Results In order to document and identify trematode parasites of the common hippopotamus ( Hippopotamus amphibius ) in artificial water systems of Zimbabwe, we applied an integrative taxonomic approach, combining molecular diagnostics and morphometrics on archived and new samples. In doing so, we provide DNA reference sequences of the hippopotamus liver fluke Fasciola nyanzae , enabling us to construct the first complete Fasciola phylogeny. We describe parasite spillback of F. nyanzae by the invasive freshwater snail Pseudosuccinea columella , as a consequence of a cascade of biological invasions in Lake Kariba, one of the biggest artificial lakes in the world. Additionally, we report an unknown stomach fluke of the hippopotamus transmitted by the non-endemic snail Radix aff. plicatula , an Asian snail species that has not been found in Africa before, and the stomach fluke Carmyerius cruciformis transmitted by the native snail Bulinus truncatus . Finally, Biomphalaria pfeifferi and two Bulinus species were found as new snail hosts for the poorly documented hippopotamus blood fluke Schistosoma edwardiense . Conclusions Our findings indicate that artificial lakes are breeding grounds for endemic and non-endemic snails that transmit trematode parasites of the common hippopotamus. This has important implications, as existing research links trematode parasite infections combined with other stressors to declining wild herbivore populations. Therefore, we argue that monitoring the anthropogenic impact on parasite transmission should become an integral part of wildlife conservation efforts. Graphical abstract

Candidozyma ( Candida ) auris is an emergent fungal pathogen of significant interest for molecular research. A handful of CRISPR-Cas9 based allele editing tools have been optimized for C. auris . Nonetheless, allele editing in this species remains a significant challenge, and different systems have different advantages and disadvantages. In this work, we compare four systems to introduce the genetic elements necessary for the production of Cas9 and the guide RNA molecule in the genome of C. auris , replacing the ENO1 , LEU2 and HIS1 loci respectively, while the fourth system makes use of an episomal plasmid. We observed that the editing efficiency of all four systems was significantly different and strain-dependent. However, we did not detect correct integration of linear CRISPR cassette constructs in integration-based systems, in over 4,900 screened transformants. Still, all transformants, whether correctly edited or not, grew on selective nourseothricin media, suggesting ectopic integration of the CRISPR cassette, which was confirmed by long-read whole genome sequencing. The plasmid-based system showed the highest editing efficiency with an average of 41.9% correct transformants, despite yielding fewer transformants compared to the other systems. Transformation of protoplasts or silencing the non-homologous end joining (NHEJ) DNA repair pathway, by deleting two main NHEJ factors, KU70 and LIG4 , did not improve the editing efficiency. While our research highlights important challenges in precise genome editing of C. auris by quantitatively evaluating the editing and targeting efficiencies of different methods, it also clearly shows the safety and usefulness of plasmid-based systems like EPIC , which we recommend for molecular work in this enigmatic fungal pathogen.

Candidozyma auris is an emerging multidrug-resistant fungal pathogen that poses a major public-health challenge owing to high mortality and the limited efficacy of current therapies. Echinocandins, which inhibit β-glucan synthesis, are first-line therapy for invasive C. auris infection; however, resistance to this class is rising, underscoring the urgent need for new antifungal targets. Here we show that enzymes in the trehalose-biosynthetic pathway regulate stress responses, antifungal resistance/tolerance and virulence in C. auris . The tps2 Δ strain displays heightened susceptibility to echinocandins, whereas tps1Δ and tps1Δ tps2Δ strains show resistance and tolerance comparable to wild type (WT). Mechanistically, the tps2Δ strain accumulates trehalose 6-phosphate (T6P), which inhibits hexokinase activity and reduces the flux of glucose 6-phosphate (G6P) into the chitin biosynthesis pathway, leading to substantially decreased cell wall chitin. During echinocandin exposure, the tps2Δ strain fails to compensate for reduced β-glucan with increased chitin, thereby rendering it highly susceptible to these drugs. In a systemic mouse infection model, deletion of the  TPS2 gene results in lower tissue fungal burdens after treatment with caspofungin. Together, these findings identify Tps2 as a potential therapeutic target that can potentiate echinocandin efficacy in C. auris via a distinct mechanism of action. Echinocandins are the first-line therapy for invasive Candidozyma auris infections, but the resistance to this drug is increasing. Here, the authors identify a potential target with a distinct mechanism of action for improving echinocandin treatment in C. auris .

A clinical case in which the combination of variation in a β‑1,3‑glucan synthase-encoding gene ( FKS2 ) and the sterol desaturase-encoding gene  ERG3 seems to underlie echinocandin resistance, prompted us to hypothesize that membrane sterol changes may modulate, rather than independently cause, Fks‑linked resistance. We were able to explore this hypothesis due to recent developments in the field, such as the release of the FungAMR database, which enables global co‑occurrence analyses; AI‑driven variant effect predictors such as Evolutionary Scale Modeling (ESM) that can explore the impact of thousands of ERG3 alleles; the cryo‑EM resolution of the Fks1 protein; and the first mechanistic model of echinocandin‑Fks1 binding. Together, these advances provide the structural and computational framework needed to delineate our hypothesis that specific sterol variants might influence β‑1,3‑glucan synthase function and drug binding. Further surveillance of this potentially epistatic interaction can be of significant clinical importance amid rising multidrug‑resistant infections, as overlooking such interactions could lead to under‑calling resistance and misguided therapy.

Evolutionary theory states that fitness determines survival. In a drug-treatment environment, resistance increases fitness, but it often comes at a cost, such as slower growth or reduced stress tolerance. If these costs are too severe, they can undermine virulence, making resistance unlikely to persist. Our study challenges this assumption. We describe the first clinical case of Nakaseomyces glabratus evolving multidrug resistance through loss-of-function mutations in ERG3 and ERG11 , despite severe fitness trade-offs. This case suggests that certain infection niches, such as the urinary tract, can provide conditions where even highly impaired yet resistant strains persist under strong antifungal pressure. Importantly, we show that this extreme resistance induces collateral sensitivity to nitroxoline, a urinary tract infection antibiotic with potent antifungal activity and a unique mechanism of action. These findings open promising therapeutic avenues to counter multidrug-resistant fungal infections of the urinary tract.

Exploring the dynamics and molecular mechanisms of antimicrobial drug resistance provides critical insights for developing effective strategies to combat it. This review highlights the potential of experimental evolution methods to study resistance in pathogenic fungi, drawing on insights from bacteriology and innovative approaches in mycology. We emphasize the versatility of experimental evolution in replicating clinical and environmental scenarios and propose that incorporating evolutionary modelling can enhance our understanding of antifungal resistance evolution. We advocate for a broader application of experimental evolution in medical mycology to improve our still limited understanding of drug resistance in fungi.

Candida auris is an opportunistic pathogenic yeast that emerged worldwide during the past decade. This fungal pathogen poses a significant public health threat due to common multidrug resistance (MDR), alarming hospital outbreaks, and frequent misidentification. Genomic analyses have identified five distinct clades that are linked to five geographic areas of origin and characterized by differences in several phenotypic traits such as virulence and drug resistance. Typing of C. auris strains and the identification of clades can be a powerful tool in molecular epidemiology and might be of clinical importance by estimating outbreak and MDR potential. As C. auris has caused global outbreaks, including in low-income countries, typing C. auris strains quickly and inexpensively is highly valuable. We report five allele-specific polymerase chain reaction (AS-PCR) assays for the identification of C. auris and each of the five described clades of C. auris based on conserved mutations in the internal transcribed spacer (ITS) rDNA region and a clade-specific gene cluster. This PCR method provides a fast, cheap, sequencing-free diagnostic tool for the identification of C. auris, C. auris clades, and potentially, the discovery of new clades.