Aldejohann, A. M. | bioRxiv Science

bioRxiv2025

Ergosterol-depleted clinical isolates of Nakaseomyces glabratus can develop multi-drug resistance without apparent fitness and virulence defects

ObjectivesNakaseomyces glabratus (formerly Candida glabrata) is a leading cause of invasive candidiasis and rapidly develops antifungal drug resistance during treatment. An increasing number of clinical isolates shows reduced susceptibility to echinocandins and azoles, leaving amphotericin B (AMB) as a last therapeutic option. Resistance of N. glabratus to this drug is rare and its underlying mechanisms are still not fully understood. Here, we describe two independent multidrug resistant (MDR) bloodstream isolates displaying resistance to AMB and anidulafungin (ANF) as well as a reduced susceptibility to azoles. MethodsWhole-genome sequencing and sterol profiling were performed on nine clinical N. glabratus isolates which were resistant to ANF and displayed resistance or low susceptibility to fluconazole (FLU) and AMB. The transcriptional response of reference strain CBS138 and an AMBR+ANFR isolate was analyzed by RNA-seq. Furthermore, PDR1 was deleted in the latter isolate to examine its influence on efflux pump gene expression. Additionally, fitness and virulence of the AMBR+ANFR isolate were examined in growth assays and a Galleria mellonella infection model. ResultsLoss of function mutations in the genes ERG3 and ERG4 is linked to ergosterol depletion and AMB resistance. Ergosterol depletion also contributed to a Pdr1-mediated up-regulation of ERG and ABC transporter genes which was associated with low FLU susceptibility. The AMBR isolates displayed no fitness defects and one of them was fully virulent in a G. mellonella infection model. ConclusionsThese findings demonstrate that ergosterol depletion in N. glabratus leads to AMB resistance without affecting fitness or virulence.

microbiology↗

bioRxiv2022

The sphingolipid inhibitor myriocin increases susceptibility of Candida auris to amphotericin B

The emerging human fungal pathogen Candida auris can cause of hospital outbreaks by transmission between patients and / or medical care staff. It is known for a fast adaption to environmental stress and antifungal treatment. Besides resistance to fluconazole in most isolates, C. auris frequently shows limited susceptibility to echinocandins and even to amphotericin B. Therefore, multidrug resistance (MDR) is frequently found in clinical isolates, leading to a need for new therapeutic targets and compounds. One of those targets could be sphingolipids which are an integral part of the cell membrane and are important for membrane fluidity and the formation of lipid rafts. Here, we show that myriocin-mediated inhibition of the de novo sphingolipid biosynthesis caused severe growth defects in C. auris. Sublethal myriocin concentrations increase fungal susceptibility to amphotericin B and anidulafungin. While the effect is limited for anidulafungin, even isolates that show phenotypic resistance to amphotericin B became susceptible in presence of myriocin. A large-scale screening of 59 clinical isolates validated these initial results and showed that inhibition of the de novo sphingolipid biosynthesis increases C. auris susceptibility to amphotericin B. These observations open new options for future therapeutic strategies and illustrate that sphingolipids might play a pivotal role for the ability of C. auris to develop resistance against amphotericin B.

microbiology↗