Comparative Analysis of Two Candida parapsilosis Isolates Originating from the Same Patient Harbouring the Y132F and R398I Mutations in the ERG11 Gene

This work presents a comparative analysis of two clinical isolates of C. parapsilosis, isolated from haemoculture (HC) and central venous catheter (CVC). Both strains harboured Y132F and R398I mutations in the gene ERG11 associated with resistance to fluconazole (FLC). Differences between the HC and CVC isolates were addressed in terms of virulence, resistance to FLC, and lipid distribution. Expression of the ERG6 and ERG9 genes, lipid analysis, fatty acid composition, and lipase activity were assessed via qPCR, thin-layer chromatography/high-performance liquid chromatography, gas chromatography, and spectrophotometry, respectively. Regulation of the ERG6 and ERG9 genes did not prove any impact on FLC resistance. Analysis of lipid metabolism showed a higher accumulation of lanosterol in both the isolates regardless of FLC presence. Additionally, a decreased level of triacylglycerols (TAG) with an impact on the composition of total fatty acids (FA) was observed for both isolates. The direct impact of the ERG11 mutations on lipid/FA analysis has not been confirmed. The higher lipase activity observed for C. parapsilosis HC isolate could be correlated with the significantly decreased level of TAG. The very close relatedness between both the isolates suggests that one isolate was derived from another after the initial infection of the host.

Modulation of ERG gene expression in fluconazole-resistant human and animal isolates of Trichophyton verrucosum

Dermatophytes are a group of eukaryotic microorganisms characterized by high capacity to colonize keratinized structures such as the skin, hair, and nails. Over the past years, the incidence of infections caused by zoophilic species, e.g., Trichophyton verrucosum, has been increasing in some parts of the world, especially in Europe. Moreover, the emergence of recalcitrant dermatophytoses and in vitro resistant dermatophytes has become a cause of concern worldwide. Here, we analyzed the mechanisms underlying resistance to fluconazole among clinical isolates of T. verrucosum. Quantitative RT-PCR was carried out to determine the relative expression levels of mRNA transcripts of ERG3, ERG6, and ERG11 genes in the fungal samples using the housekeeping gene GAPDH as a reference. Our results showed that the upregulation of the ERG gene expression is a possible mechanism of resistance to fluconazole in this species. Furthermore, ERG11 is the most statistically significantly overexpressed gene in the pool of fluconazole-resistant T. verrucosum isolates. Additionally, we have demonstrated that exposure to fluconazole increases the levels of expression of ERG genes in fluconazole-resistant isolates of T. verrucosum. In conclusion, this study has shown one of the possible mechanisms of resistance to fluconazole among zoophilic dermatophytes, which involves the maintenance of high levels of expression of ERG genes after drug exposure.

Citronellal Exerts Its Antifungal Activity by Targeting Ergosterol Biosynthesis in Penicillium digitatum

Ergosterol (ERG) is a potential target for the development of antifungal agents against Penicillium digitatum, the pathogen of green mold in citrus fruits. This study examined the mechanism by which citronellal, a typical terpenoid of Cymbopogon nardus essential oil, acts on ergosterol to exhibit its antifungal activity against P. digitatum. We previously reported that citronellal inhibited the growth of P. digitatum with minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 1.36 and 2.72 mg/mL, respectively. In citronellal-treated cells, the membrane integrity and ergosterol contents significantly decreased, whereas lanosterol, which serves as a precursor for ergosterol biosynthesis, massively accumulated. Addition of 150 mg/L of exogenous ergosterol decreased the inhibitory rate of citronellal, restoring the ergosterol content and hence the membrane structure to normal levels, and triggered expression of nearly all ERG genes. Based on our findings, we deduce that citronellal damages the cell membrane integrity of P. digitatum by down-regulating the ERG genes responsible for conversion of lanosterol to ergosterol, the key downregulated gene being ERG3, due to the observed accumulation of ergosta-7,22-dienol.

Modulation of ERG Genes Expression in Clinical Isolates of Candida tropicalis Susceptible and Resistant to Fluconazole and Itraconazole

Candida tropicalis is a non-albicans Candida specie that causes candidosis in several countries, including Brazil. However, little is known about the mechanisms of drug resistance in C. tropicalis infections. In this study, we used clinical isolates of C. tropicalis susceptible as well as resistant to either Fluconazole or Itraconazole to assess the relationship between drug resistance and the expression of ERG and efflux pump genes. Our results showed that the main mechanism of resistance against both Fluconazole and Itraconazole in this specie is through the up-regulation of ERG rather than that of the efflux pump genes. We demonstrated that, although pre-treatment with azole drugs increases the expression of both ERG6 and ERG11 genes, the resistant or susceptible dose-dependent (SDD) samples are able to maintain high expression levels of these genes for longer periods of time than the susceptible samples.

Effect of Voriconazole on Candida tropicalis Biofilms: Relation with ERG Genes Expression

Candida tropicalis has emerged as the third most prevalent fungal pathogens and its ability to form biofilms has been considered one of the most important virulence factors, since biofilms represent high tolerance to antifungal agents. However, the mechanisms of C. tropicalis biofilm resistance to antifungals remain poorly understood. Thus, the main aim of this work was to infer about the effect of voriconazole on the formation and control of C. tropicalis biofilms and disclose its relationship with ERG genes' expression. Planktonic cells tolerance of several C. tropicalis clinical isolates to voriconazole was determined through of antifungal susceptibility test, and the effect of this azole against C. tropicalis biofilm formation and pre-formed biofilms was evaluated by cultivable cells determination and total biomass quantification. ERG genes expression was analyzed by quantitative real-time polymerase chain reaction. This work showed that C. tropicalis resistance to voriconazole is strain dependent and that voriconazole was able to partially control biofilm formation, but was unable to eradicate C. tropicalis pre-formed biofilms. Moreover, C. tropicalis biofilms resistance to voriconazole seems to be associated with alterations of sterol content in the cell membrane, resulting in ERG genes overexpression. Voriconazole is unable to control C. tropicalis biofilms, and the overexpression of ERG genes is a possible mechanism of biofilm resistance.