PubMed · 14166740
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M GENTILINI, L JOUFFROY. 1964. [CRYPTOCOCCOSIS].. https://pubmed.ncbi.nlm.nih.gov/14166740/
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Clinical isolates of Candida auris show a high prevalence of resistance to Amphotericin B (AmB)-an uncommon trait in most Candida species. Alterations in ergosterol biosynthesis can contribute to acquired AmB resistance in C. auris laboratory strains but are rarely seen in clinical isolates. In this study, we experimentally evolved two drug-susceptible Clade II isolates of C. auris to develop AmB resistance. The evolved strains displayed a four to eight fold increase in MIC50 compared to the parental cells. We analyzed changes in their karyotype, genome, lipidome, and transcriptome associated with this acquired resistance. In one lineage, AOX2 was upregulated, and its deletion reversed the AmB resistance phenotype. The aox2Δ mutant also failed to evolve AmB resistance under experimental conditions. In the same lineage, restoring the UPC2 S332R and RTG3 S101T mutations to the wild-type allele restored AmB susceptibility. In another lineage, the ergosterol and sphingolipid pathways were observed to play a critical role, and upregulation of the ERG genes elevated the total sterol content, while significant downregulation of HSX11 (glucosylceramide synthase) resulted in lower levels of glucosylceramides. To our knowledge, this study is the first to show that AmB resistance in C. auris can be acquired through mechanisms both dependent on or independent of sterol content modulation, highlighting Aox2 and Upc2 as key regulators of amphotericin resistance.
Amphotericin B is a medically important antifungal antibiotic that is produced by Streptomyces nodosus. Genetic manipulation of this organism has led to production of the first amphotericin analogues by engineered biosynthesis. Here, these studies were extended by sequencing the chromosomal regions flanking the amphotericin polyketide synthase genes, and by refining the phage KC515 transduction method for disruption and replacement of S. nodosus genes. A hybrid vector was constructed from KC515 DNA and the Escherichia coli plasmid pACYC177. This vector replicated as a plasmid in E. coli and the purified DNA yielded phage plaques on Streptomyces lividans after polyethylene glycol (PEG)-mediated transfection of protoplasts. The left flank of the amphotericin gene cluster was found to include amphRI, RII, RIII and RIV genes that are similar to regulatory genes in other polyene biosynthetic gene clusters. One of these regulatory genes, amphRI, was found to have a homologue, amphRVI, located in the right flank at a distance of 127 kbp along the chromosome. However, disruption of amphRVI using the hybrid vector had no effect on the yield of amphotericin obtained from cultures grown on production medium. The hybrid vector was also used for precise deletion of the DNA coding for two modules of the AmphC polyketide synthase protein. Analysis by UV spectrophotometry revealed that the deletion mutant produced a novel pentaene, with reduced antifungal activity but apparently greater water-solubility than amphotericin B. This shows the potential for use of the new vector in engineering of this and other biosynthetic pathways in Streptomyces.
OBJECTIVES: We have investigated the use of a viability dye, chloromethylfluorescein di-acetate (CMFDA), for antifungal susceptibility testing in a fluorescence microplate (FM) assay format. METHODS: For this FM assay, conidia were incubated in increasing concentrations of antifungal drug for 16 h and stained with CMFDA. Fluorescence, measured as mean fluorescence units (MFU) in a fluorescence microplate reader, was graphed relative to that of a drug-free control, and the MIC was defined as the lowest concentration of the drug that resulted in complete reduction (100%) in MFU for amphotericin B, or 90% reduction in MFU for itraconazole and voriconazole. Susceptibilities of 10 clinical isolates of Aspergillus fumigatus, Aspergillus terreus and Aspergillus niger to amphotericin B, itraconazole and voriconazole were tested in a blinded fashion using the FM and the NCCLS methods. RESULTS AND CONCLUSIONS: Reproducibility of the FM assay was excellent, and results correlated with those of the NCCLS microdilution method. The FM assay appears to be a rapid, objective method for testing fungal susceptibilities to itraconazole, voriconazole and amphotericin B.