Candida albicans is an opportunistic fungal pathogen of humans. Treatment of C. albicans infections relies on azoles, which target the lanosterol 14α-demethylase (Erg11p) encoded by the ERG11 gene. Our results show that targeted gene disruption of ERG11 can result in resistance to ergosterol-dependent drugs (azoles and amphotericin B), auxotrophy and aerobically viable erg11Δ/Δ cells. Abnormal sterol deposition and lack of ergosterol in the erg11Δ/Δ strain leads to reduced plasma membrane (PM) fluidity, as well as dysfunction of the vacuolar and mitochondrial membranes, resulting respectively in defects in vacuole fusion and a reduced intracellular ATP level. The altered PM structure of the erg11Δ/Δ strain contributes to delocalisation of H⁺-ATPase and the Cdr1 efflux pump from the PM to vacuoles and, resulting in a decrease in PM potential (Δψ) and increased sensitivity to ergosterol-independent xenobiotics. This new insight into intracellular processes under Erg11p inhibition may lead to a better understanding of the indirect effects of azoles on C. albicans cells and the development of new treatment strategies for resistant infections.

Adherence of the fungus, Candida albicans, to biotic (e.g. human tissues) and abiotic (e.g. catheters) surfaces can lead to emergence of opportunistic infections in humans. The process of adhesion and further biofilm development depends, in part, on cell surface hydrophobicity (CSH). In this study, we compared the resistance of C. albicans strains with different CSH to the most commonly prescribed antifungal drug, fluconazole, and the newly described synergistic combination, fluconazole and gentamicin. The hydrophobic strain was more resistant to fluconazole due to, among others, overexpression of the ERG11 gene encoding the fluconazole target protein (CYP51A1, Erg11p), which leads to overproduction of ergosterol in this strain. Additionally, the hydrophobic strain displayed high efflux activity of the multidrug resistance Cdr1 pump due to high expression of the CDR1 gene. On the other hand, the hydrophobic C. albicans strain was more susceptible to fluconazole–gentamicin combination because of its different effect on lipid content in the two strains. The combination resulted in ergosterol depletion with subsequent Cdr1p mislocalization and loss of activity in the hydrophobic strain. We propose that C. albicans strains with different CSH may possess altered lipid metabolism and consequently may differ in their response to treatment.

A reaction of bis[(2-chlorocarbonyl)phenyl] diselenide with various mono and bisnucleophiles such as aminophenols, phenols, and amines have been studied as a convenient general route to a series of new antimicrobial and antiviral diphenyl diselenides. The compounds, particularly bis[2-(hydroxyphenylcarbamoyl)]phenyl diselenides and reference benzisoselenazol-3(2H)-ones, exhibited high antimicrobial activity against Gram-positive bacterial species (Enterococcus spp., Staphylococcus spp.), and some compounds were also active against Gram-negative E. coli and fungi (Candida spp., A. niger). The majority of compounds demonstrated high activity against human herpes virus type 1 (HHV-1) and moderate activity against encephalomyocarditis virus (EMCV), while they were generally inactive against vesicular stomatitis virus (VSV).

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.

Candida albicans is a pathogenic fungus that is increasingly developing multidrug resistance (MDR), including resistance to azole drugs such as fluconazole (FLC). This is partially a result of the increased synthesis of membrane efflux transporters Cdr1p, Cdr2p, and Mdr1p. Although all these proteins can export FLC, only Cdr1p is expressed constitutively. In this study, the effect of elevated fructose, as a carbon source, on the MDR was evaluated. It was shown that fructose, elevated in the serum of diabetics, promotes FLC resistance. Using C. albicans strains with green fluorescent protein (GFP) tagged MDR transporters, it was determined that the FLC-resistance phenotype occurs as a result of Mdr1p activation and via the increased induction of higher Cdr1p levels. It was observed that fructose-grown C. albicans cells displayed a high efflux activity of both transporters as opposed to glucose-grown cells, which synthesize Cdr1p but not Mdr1p. Additionally, it was concluded that elevated fructose serum levels induce the de novo production of Mdr1p after 60 min. In combination with glucose, however, fructose induces Mdr1p production as soon as after 30 min. It is proposed that fructose may be one of the biochemical factors responsible for Mdr1p production in C. albicans cells.

Candida albicans is an opportunistic pathogen that induces vulvovaginal candidiasis (VVC), among other diseases. In the vaginal environment, the source of carbon for C. albicans can be either lactic acid or its dissociated form, lactate. It has been shown that lactate, similar to the popular antifungal drug fluconazole (FLC), reduces the expression of the ERG11 gene and hence the amount of ergosterol in the plasma membrane. The Cdr1 transporter that effluxes xenobiotics from C. albicans cells, including FLC, is delocalized from the plasma membrane to a vacuole under the influence of lactate. Despite the overexpression of the CDR1 gene and the increased activity of Cdr1p, C. albicans is fourfold more sensitive to FLC in the presence of lactate than when glucose is the source of carbon. We propose synergistic effects of lactate and FLC in that they block Cdr1 activity by delocalization due to changes in the ergosterol content of the plasma membrane.