Antimycotic Drugs and their Mechanisms of Resistance to Candida Species

Nosocomial transmission of fluconazole-resistant Candida glabrata bloodstream isolates revealed by whole-genome sequencing

The clonal transmission of fluconazole-resistant Candida glabrata isolates within hospitals has seldom been analyzed by whole-genome sequencing (WGS). We performed WGS on 79 C. glabrata isolates, comprising 31 isolates from three premature infants with persistent C. glabrata bloodstream infection despite antifungal treatment in the same neonatal intensive care unit (NICU) in 2022 and 48 (27 fluconazole-resistant and 21 fluconazole-susceptible dose-dependent) bloodstream isolates from 48 patients in 15 South Korean hospitals from 2010 to 2022. Phylogenetic analysis based on WGS single-nucleotide polymorphisms (SNPs) distinguished the 79 isolates according to multilocus sequence typing (MLST) (17 sequence type [ST]3, 13 ST7, two ST22, 41 ST26, four ST55, and two ST59 isolates) and unveiled two possible clusters of nosocomial transmission among ST26 isolates. One cluster from two premature infants with overlapping NICU hospitalizations in 2022 encompassed 15 fluconazole-resistant isolates harboring pleiotropic drug-resistance transcription factor (Pdr1p) P258L (13 isolates) or N1086I (two isolates), together with 10 fluconazole-susceptible dose-dependent isolates lacking Pdr1p SNPs. The other cluster indicated unforeseen clonal transmission of fluconazole-resistant bloodstream isolates among five patients (four post-lung transplantation and one with diffuse interstitial lung disease) in the same hospital over 8 months. Among these five isolates, four obtained after exposure to azole antifungals harbored distinct Pdr1p SNPs (N1091D, E388Q, K365E, and R376Q). The findings reveal the transmission patterns of clonal bloodstream isolates of C. glabrata among patients undergoing antifungal treatment, exhibiting different levels of fluconazole susceptibility or distinct Pdr1p SNP profiles.

IMPORTANCE

The prevalence of fluconazole-resistant bloodstream infections caused by Candida glabrata is increasing globally, but the transmission of these resistant strains within hospitals has rarely been documented. Through whole-genome sequencing and epidemiological analyses, this study identified two potential clusters of C. glabrata bloodstream infections within the same hospital, revealing the transmission of clonal C. glabrata strains with different levels of fluconazole susceptibility or distinct transcription factor pleiotropic drug resistance protein 1 (Pdr1p) single-nucleotide polymorphism profiles among patients receiving antifungal therapy.

Protein fraction from Sesbania virgata (Cav.) Pers. seeds exhibit antioxidant and antifungal activities

Sesbania virgata (Cav.) Pers. seeds are protein sources with health and environmental benefits. In this research, proteins with lectin activity were identified in a protein fraction from S. virgata seeds (PFLA), as well its antioxidant and antimicrobial potentials, in addition to cytotoxic effects. To obtain PFLA, seed flour was homogenized in Glycine-NaOH (100 mM; pH 9.0; NaCl 150 mM) and precipitated in ammonium sulfate. PFLA concentrates bioactive lectins (32 HU/mL, 480 HU/gFa, 18.862 HU/mgP) and essential amino acids (13.36 g/100g protein). PFLA exerts antioxidant activity, acting as a promising metal chelating agent (~77% of activity). Analyzes of cell culture assay results suggest that antioxidant activity of PFLA may be associated with the recruitment of essential molecules to prevent the metabolic impairment of cells exposed to oxidative stress. PFLA (256 - 512 µg/mL) also exhibits antifungal activity, inhibiting the growth of Aspergillus flavus, Candida albicans, Candida tropicalis and Penicillium citrinum. Cytotoxic analysis indicates a tendency of low interference in the proliferation of 3T3 and HepG2 cells in the range of PFLA concentrations with biological activity. These findings support the notion that PFLA is a promising adjuvant to be applied in current policies on the management of metal ion chelation and fungal infections.

Design, synthesis and evaluation of 2-phenylpyrimidine derivatives as novel antifungal agents targeting CYP51

Invasive fungal infections, with high morbidity and mortality, have become one of the most serious threats to human health. There are a few kinds of clinical antifungal drugs but large amounts of them are used, so there is an urgent need for a new structural type of antifungal drug. In this study, we carried out three rounds of structural optimisation and modification of the compound YW-01, which was obtained from the preliminary screening of the group, by using the strategy of scaffold hopping. A series of novel phenylpyrimidine CYP51 inhibitors were designed and synthesised. In vitro antifungal testing showed that target compound C6 exhibited good efficacy against seven common clinically susceptible strains, which was significantly superior to the clinical first-line drug fluconazole. Subsequently in vitro tests on metabolic stability and cytotoxicity revealed that C6 was safe and stable for hepatic microsomal function. Finally, C6 warranted further exploration as a possible novel structural type of CYP51 inhibitor.

RNA-Seq-Based Transcriptomics and GC-MS Quantitative Analysis Reveal Antifungal Mechanisms of Essential Oil of Clausena lansium (Lour.) Skeels Seeds against Candida albicans

Infections caused by Candida albicans (C. albicans) and increasing resistance to commonly used drugs lead to a variety of mucosal diseases and systemic infectious diseases. We previously confirmed that the essential oil of Clausena lansium (Lour.) Skeels seeds (CSEO) had antifungal activity against C. albicans, but the detailed mechanism between the chemical components and antifungal activity is unclear. In this study, a quantitative analysis of five volatile components of CSEO, including sabinene, α-phellandrene, β-phellandrene, 4-terpineol, and β-caryophyllene, was carried out using the gas chromatography-mass spectrometry (GC-MS) method. Both the broth dilution and kinetic growth methods proved that the antifungal activity of CSEO against fluconazole-resistant C. albicans was better than that of its main components (sabinene and 4-terpineol). To further investigate the inhibitory mechanism, the transcriptional responses of C. albicans to CSEO, sabinene, and 4-terpineol treatment were determined based on RNA-seq. The Venn diagram and clustering analysis pattern of differential expression genes showed the mechanism of CSEO and 4-terpineol's anti-C. albicans activity might be similar from the perspective of the genes. Functional enrichment analysis suggested that CSEO regulated adherence-, hyphae-, and biofilm-formation-related genes, which may be CSEO's active mechanism of inhibiting the growth of fluconazole-resistant C. albicans. Overall, we preliminarily revealed the molecular mechanism between the chemical components and the antifungal activity of CSEO against C. albicans. This study provides new insights to overcome the azole resistance of C. albicans and promote the development and application of C. lansium (Lour.) Skeels seeds.

The Role of Novel Antifungals in the Management of Candidiasis: A Clinical Perspective

Mucosal and invasive candidiasis can be challenging to treat in the setting of drug intolerance, antifungal resistance, drug-drug interactions, or host immune status. Antifungals with novel mechanisms of action and distinct pharmacokinetic/pharmacodynamic properties have been developed in recent years. Rezafungin is an echinocandin with high-tissue penetration and an extended half-life that allows for once-weekly administration, making it a convenient treatment option for invasive candidiasis while obviating the need for central catheter placement. Ibrexafungerp is an oral glucan synthase inhibitor that is active against most echinocandin-resistant Candida species. At present, it is approved for the treatment of acute vulvovaginal candidiasis and is under investigation as an oral step-down therapy following initial treatment with an echinocandin for cases of invasive candidiasis. Oteseconazole is a long-acting tetrazole that exhibits a higher affinity for the fungal enzyme CYP51, resulting in a potentially lower risk of drug-drug interactions and side effects compared to other azoles. It is currently approved for the treatment of recurrent vulvovaginal candidiasis. Fosmanogepix has a novel mechanism of action and potent activity against several Candida strains resistant to other antifungals. Due to its considerable bioavailability and tissue penetration, it holds promise as a potential treatment option in patients with invasive candidiasis, including those with chorioretinitis or meningitis. Results from clinical trials and observational studies will further delineate the role of these agents in the management of candidiasis. As the usage of these novel antifungals becomes widespread, we expect to acquire a greater understanding of their efficacy and potential benefits.

Activity of propolis from Mexico on the proliferation and virulence factors of Candida albicans

BACKGROUND

This research evaluated the anti-Candida albicans effect of Mexican propolis from Chihuahua. Chemical composition of the ethanolic extract of propolis was determined by GC-MS, HPLC-DAD, and HPLC-MS. The presence of anthraquinone, aromatic acid, fatty acids, flavonoids, and carbohydrates was revealed.

RESULTS

The anti-Candida activity of propolis was determined. The inhibitions halos were between 10.0 to 11.8 mm; 25% minimum inhibitory concentration (0.5 mg/ml) was fungistatic, and 50% minimum inhibitory concentration (1.0 mg/ml) was fungicidal. The effect of propolis on the capability of C. albicans to change its morphology was evaluated. 25% minimum inhibitory concentration inhibited to 50% of germ tube formation. Staining with calcofluor-white and propidium iodide was performed, showing that the propolis affected the integrity of the cell membrane. INT1 gene expression was evaluated by qRT-PCR. Propolis significantly inhibited the expression of the INT1 gene encodes an adhesin (Int1p). Chihuahua propolis extract inhibited the proliferation of Candida albicans, the development of the germ tube, and the synthesis of adhesin INT1.

CONCLUSIONS

Given the properties demonstrated for Chihuahua propolis, we propose that it is a candidate to be considered as an ideal antifungal agent to help treat this infection since it would not have the toxic effects of conventional antifungals.

Inhibitory Effects of a Maleimide Compound on the Virulence Factors of Candida albicans

Candidiasis caused by Candida albicans infection has long been a serious human health problem. The pathogenicity of C. albicans is mainly due to its virulence factors, which are the novel targets of antifungal drugs for low risk of resistance development. In this study, we identified a maleimide compound [1-(4-methoxyphenyl)-1hydro-pyrrole-2,5-dione, MPD] that exerts effective anti-virulence activity. It could inhibit the process of adhesion, filamentation, and biofilm formation in C. albicans. In addition, it exhibited low cytotoxicity, hemolytic activity and drug resistance development. Moreover, in Galleria mellonella-C. albicans (in vivo) infection model, the survival time of infected larvae was significantly prolonged under the treatment of MPD. Further, mechanism research revealed that MPD increased farnesol secretion by upregulating the expression of Dpp3. The increased farnesol inhibited the activity of Cdc35, which then decreased the intracellular cAMP content resulting in the inhibition of virulence factors via the Ras1-cAMP-Efg1 pathway. In all, this study evaluated the inhibitory effect of MPD on various virulence factors of C. albicans and identified the underlying mechanisms. This suggests a potential application of MPD to overcome fungal infections in clinic.

Whole-Genome Sequence Analysis of Candida glabrata Isolates from a Patient with Persistent Fungemia and Determination of the Molecular Mechanisms of Multidrug Resistance

Whole-genome sequencing (WGS) was used to determine the molecular mechanisms of multidrug resistance for 10 serial Candida glabrata bloodstream isolates obtained from a neutropenic patient during 82 days of amphotericin B (AMB) or echinocandin therapy. For WGS, a library was prepared and sequenced using a Nextera DNA Flex Kit (Illumina) and the MiseqDx (Illumina) instrument. All isolates harbored the same Msh2p substitution, V239L, associated with multilocus sequence type 7 and a Pdr1p substitution, L825P, that caused azole resistance. Of six isolates with increased AMB MICs (≥2 mg/L), three harboring the Erg6p A158fs mutation had AMB MICs ≥ 8 mg/L, and three harboring the Erg6p R314K, Erg3p G236D, or Erg3p F226fs mutation had AMB MICs of 2-3 mg/L. Four isolates harboring the Erg6p A158fs or R314K mutation had fluconazole MICs of 4-8 mg/L while the remaining six had fluconazole MICs ≥ 256 mg/L. Two isolates with micafungin MICs > 8 mg/L harbored Fks2p (I661_L662insF) and Fks1p (C499fs) mutations, while six isolates with micafungin MICs of 0.25-2 mg/L harbored an Fks2p K1357E substitution. Using WGS, we detected novel mechanisms of AMB and echinocandin resistance; we explored mechanisms that may explain the complex relationship between AMB and azole resistance.

Preliminary Studies on the Mechanism of Antifungal Activity of New Cationic β-Glucan Derivatives Obtained from Oats and Barley

New chemical structures with antifungal properties are highly desirable from the point of view of modern pharmaceutical science, especially due to the increasingly widespread instances of drug resistance in the case of these diseases. One way to solve this problem is to use polymeric drugs, widely described as biocidal, positively charged macromolecules. In this work, we present the synthesis of new cationic β-glucan derivatives that show selective antifungal activity and at the same time low toxicity toward animal and human cells. Two β-glucans isolated from oats and barley and modified using glycidyltrimethylammonium chloride were obtained and evaluated for biocidal properties on the cells of mammals and pathogenic fungi and bacteria. These compounds were found to be nontoxic to fibroblast and bacterial cells but showed selective toxicity to certain species of filamentous fungi (Scopulariopsis brevicaulis) and yeasts (Cryptococcus neoformans). The most important aspect of this work is the attempt to explain the mechanisms of action of these compounds by studying their interaction with biological membranes. This was achieved by examining the interactions with model biological membranes representative of given families of microorganisms using Langmuir monolayers. The data obtained partly show correlations between the results for model systems and biological experiments and allow indicating that the selective antifungal activity of cationic β-glucans is related to their interaction with fungal biological membranes and partly lack of such interaction toward cells of other organisms. In addition, the obtained macromolecules were characterized by spectral methods (Fourier transform infrared (FTIR) and ¹H nuclear magnetic resonance (NMR) spectroscopies) to confirm that the desired structure was obtained, and their degree of modification and molecular weights were determined.

Inhibitory Effects and Mechanism of Action of Elsinochrome A on Candida albicans and Its Biofilm

Biofilm-associated Candida albicans infections, the leading cause of invasive candidiasis, can cause high mortality rates in immunocompromised patients. Photodynamic antimicrobial chemotherapy (PACT) is a promising approach for controlling infections caused by biofilm-associated C. albicans. This study shows the effect of Elsinochrome A (EA) against different stages of C. albicans biofilms in vitro by XTT reduction assay and crystal violet staining. The mechanism of action of EA on C. albicans biofilm was analyzed with flow cytometry, confocal laser microscopy, and the Real-Time Quantitative Reverse Transcription PCR (qRT-PCR). EA-mediated PACT significantly reduced the viability of C. albicans, with an inhibition rate on biofilm of 89.38% under a concentration of 32 μg/mL EA. We found that EA could not only inhibit the adhesion of C. albicans in the early stage of biofilm formation, but that it also had good effects on pre-formed mature biofilms with a clearance rate of 35.16%. It was observed that EA-mediated PACT promotes the production of a large amount of reactive oxygen species (ROS) in C. albicans and down-regulates the intracellular expression of oxidative-stress-related genes, which further disrupted the permeability of cell membranes, leading to mitochondrial and nuclear damage. These results indicate that EA has good photodynamic antagonizing activity against the C. albicans biofilm, and potential clinical value.