Comparative Study of the Effects of Fluconazole and Voriconazole on Candida glabrata, Candida parapsilosis and Candida rugosa Biofilms

Synthesis of Benzimidazole-1,2,4-triazole Derivatives as Potential Antifungal Agents Targeting 14α-Demethylase

Invasive fungal infections (IFIs) are increasing as major infectious diseases around the world, and the limited efficacy of existing medications has resulted in substantial morbidity and death in patients due to the lack of effective antifungal agents and serious drug resistance. In this study, a series of benzimidazole-1,2,4-triazole derivatives (6a-6l) were synthesized and characterized by ¹H NMR, ¹³C NMR, and HR-MS spectral analysis. All the target compounds were screened for their in vitro antifungal activity against four fungal strains, namely, C. albicans, C. glabrata, C. krusei, and C. parapsilopsis. The synthesized compounds exhibited significant antifungal potential, especially against C. glabrata. Three compounds (6b, 6i, and 6j) showed higher antifungal activity with their MIC values (0.97 μg/mL) compared with voriconazole and fluconazole. Molecular docking provided a possible binding mode of compounds 6b, 6i, and 6j in the 14α-demethylase active site. Our studies suggested that the benzimidazole-1,2,4-triazole derivatives can be used as a new fungicidal lead targeting 14α-demethylase for further structural optimization. In addition, their effects on the L929 cell line were also investigated to evaluate the cytotoxic effects of the compounds. SEM analyses were performed to examine the effects of compounds 6a, 6i, and 6j on C. glabrata cells under in vivo experimental conditions.

Scanning ion-conductance microscopy technique for studying the topography and mechanical properties of Candida parapsilosis yeast microorganisms

Super-resolution microscopy is widely used in the development of novel antimicrobial testing in vitro. In the presented work, a scanning protocol was developed by the method of scanning ion-conducting microscopy (SICM), which makes it possible to study microorganisms without rigid fixation and in saline, obtaining an index map of nanosized structures. The effect of azole and echinocandins drugs on the morphology and mechanical properties of Candida parapsilosis yeast was studied. The findings are consistent with previously proposed drug mechanisms and reports that have examined antifungal agents using AFM, SEM, and TEM. We have shown that the SICM method is capable of scanning and detecting the nanomechanical properties of yeast non-invasively.

Wild Boar (Sus scrofa) as Reservoir of Zoonotic Yeasts: Bioindicator of Environmental Quality

Wildlife animals are recognized as reservoirs for zoonotic fungi and their faeces might play an important role in introducing pathogens into the environment. Thought wild boar (Sus scrofa) population has dramatically increased across Europe, information about their possible role in dissemination of zoonotic pathogenic yeasts in the environment is scant. Therefore, fecal samples (n = 124) from wild boars from Campania region (Southern Italy) were collected and yeasts identified biochemically and molecularly by sequencing of the internal transcribed spacer region and their phylogenetical relationship assessed. The antifungal susceptibility profiles of yeasts were also investigated using AFST-EUCAST method. Yeasts were isolated from 50.1% of the samples with the highest occurrence in samples from the province of Salerno (61.1%). A total of 368 Candida strains belonging to nine species were identified, with Candida albicans (45.7%), followed by Candida krusei (15.2%), Kazachstania slooffiae (9.8%) and Candida parapsilosis (7.6%) as the most prevalent identified species. Among C. albicans four sequence types (i.e., ST1-ST4) were identified with an intraspecific nucleotide difference up to 0.21%. The ML tree grouped all representative sequence types as paraphyletic clades with those of the references yeast species, respectively and supported by high bootstrap values. Fluconazole was the less active drug whereas, posaconazole, voriconazole, and isavuconazole the most active one. No resistance phenomena were observed for C. albicans and high MICs values for 5FC, azoles and echinocandines were registered in non-albicans Candida spp. This study showed, for the first time, the important role of wild boars in dissemination of pathogenic fungi in the environment. The absence of resistance phenomena in the Candida spp. might reflect environmental free from residues of azoles antifungals pollution or chemicals and suggests the role of wild boar as bio indicators of environment quality.

Copper(II) and Zinc(II) Complexes with the Clinically Used Fluconazole: Comparison of Antifungal Activity and Therapeutic Potential

Copper(II) and zinc(II) complexes with clinically used antifungal drug fluconazole (fcz), {[CuCl2(fcz)2].5H2O}n, 1, and {[ZnCl2(fcz)2]·2C2H5OH}n, 2, were prepared and characterized by spectroscopic and crystallographic methods. The polymeric structure of the complexes comprises four fluconazole molecules monodentately coordinated via the triazole nitrogen and two chlorido ligands. With respect to fluconazole, complex 2 showed significantly higher antifungal activity against Candida krusei and Candida parapsilosis. All tested compounds reduced the total amount of ergosterol at subinhibitory concentrations, indicating that the mode of activity of fluconazole was retained within the complexes, which was corroborated via molecular docking with cytochrome P450 sterol 14α-demethylase (CYP51) as a target. Electrostatic, steric and internal energy interactions between the complexes and enzyme showed that 2 has higher binding potency to this target. Both complexes showed strong inhibition of C. albicans filamentation and biofilm formation at subinhibitory concentrations, with 2 being able to reduce the adherence of C. albicans to A549 cells in vitro. Complex 2 was able to reduce pyocyanin production in Pseudomonas aeruginosa between 10% and 25% and to inhibit its biofilm formation by 20% in comparison to the untreated control. These results suggest that complex 2 may be further examined in the mixed Candida-P. aeruginosa infections.

Emerging Roles of Functional Bacterial Amyloids in Gene Regulation, Toxicity, and Immunomodulation

Bacteria often reside in multicellular communities, called biofilms, held together by an extracellular matrix. In many bacteria, the major proteinaceous component of the biofilm are amyloid fibers. Amyloids are highly stable and structured protein aggregates which were known mostly to be associated with neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases. In recent years, microbial amyloids were identified also in other species and shown to play major roles in microbial physiology and virulence. For example, amyloid fibers assemble on the bacterial cell surface as a part of the extracellular matrix and are extremely important to the scaffolding and structural integrity of biofilms, which contribute to microbial resilience and resistance. Furthermore, microbial amyloids play fundamental nonscaffold roles that contribute to the development of biofilms underlying numerous persistent infections. Here, we review several nonscaffold roles of bacterial amyloid proteins, including bridging cells during collective migration, acting as regulators of cell fate, as toxins against other bacteria or against host immune cells, and as modulators of the hosts' immune system. These overall points on the complexity of the amyloid fold in encoding numerous activities, which offer approaches for the development of a novel repertoire of antivirulence therapeutics.

Fluconazole and Lipopeptide Surfactin Interplay During Candida albicans Plasma Membrane and Cell Wall Remodeling Increases Fungal Immune System Exposure

Recognizing the β-glucan component of the Candida albicans cell wall is a necessary step involved in host immune system recognition. Compounds that result in exposed β-glucan recognizable to the immune system could be valuable antifungal drugs. Antifungal development is especially important because fungi are becoming increasingly drug resistant. This study demonstrates that lipopeptide, surfactin, unmasks β-glucan when the C. albicans cells lack ergosterol. This observation also holds when ergosterol is depleted by fluconazole. Surfactin does not enhance the effects of local chitin accumulation in the presence of fluconazole. Expression of the CHS3 gene, encoding a gene product resulting in 80% of cellular chitin, is downregulated. C. albicans exposure to fluconazole changes the composition and structure of the fungal plasma membrane. At the same time, the fungal cell wall is altered and remodeled in a way that makes the fungi susceptible to surfactin. In silico studies show that surfactin can form a complex with β-glucan. Surfactin forms a less stable complex with chitin, which in combination with lowering chitin synthesis, could be a second anti-fungal mechanism of action of this lipopeptide.

In vitro virulence determinants, comparative pathogenicity of Diutina (Candida) mesorugosa clinical isolates and literature review of the D. rugosa complex

Opportunistic mycoses by yeasts have increased considerably in the last three decades. Although Candida albicans is considered one of the most important causes of nosocomial infections, there is a recent shift to non-albicans Candida species as the most frequently isolated yeasts in particular risk groups. Diutina rugosa (formerly Candida rugosa) is a complex that includes four species: D. rugosa sensu stricto, D. neorugosa, D. pseudorugosa, and D. mesorugosa, and they are estimated to represent 0.2% of all Candida clinical isolates. In this study, we analyze nine clinical isolates of D. mesorugosa with focus on the virulence determinants and pathogenicity of the species by means of a Galleria mellonella survival model. Overall, we detected very strong aspartyl-protease and esterase activities. In contrast, both DNase and hemolysin activities were evident in only two of the isolates. None of the isolates was positive for phospholipase activity. All isolates studied were able to form biofilm after 72 h of incubation in a robust manner when compared with the C. albicans strain used as control. Susceptibility testing showed minimum inhibitory concentrations (MICs) ≤1 µg/mL for amphotericin B in all isolates tested. Eight out of nine of the isolates had MICs ≤2 µg/mL for fluconazole. All isolates were resistant to both anidulafungin and caspofungin (MICs ≥1 µg/mL). We found a significant difference (P < 0.0001) amongst the survival curves for the different D. mesorugosa isolates in the Galleria mellonella survival model. Strains HPM309 and H259 produced an acute infection and exhibited the highest virulence, whereas the D. mesorugosa isolates 99-480 and DM17 proved to be the less virulent strains.