Effect of Farnesol on Growth, Ergosterol Biosynthesis, and Cell Permeability in Coccidioides posadasii

Abstract

Coccidioidomycosis is a systemic mycosis caused by the dimorphic fungi Coccidioides spp. The treatment for chronic and/or disseminated coccidioidomycosis can be prolonged and complicated. Therefore, the search for new drugs is necessary. Farnesol is a precursor in the sterol biosynthesis pathway that has been shown to present antifungal activity. Thus, the objective of this study was to evaluate the in vitro antifungal activity of farnesol alone and in combination with antifungal agents against clinical and environmental strains of Coccidioides posadasii as well as to determine their effect on the synthesis of ergosterol and on cell permeability. This study employed the broth macrodilution method to determine the MIC of farnesol against 18 strains of C. posadasii. Quantification of ergosterol was performed with 10 strains of C. posadasii after exposure to subinhibitory concentrations of farnesol. Finally, the activity of farnesol was evaluated in the presence of osmotic stress, induced by the addition of NaCl to the culture medium, during the susceptibility tests. The results showed that farnesol exhibited low MICs (ranging from 0.00171 to 0.01369 mg/liter) against all tested strains. The combination of farnesol with the antifungals showed synergistic effects (fractional inhibitory concentration index [FICI] < 0.5). As for the ergosterol quantification, it was observed that exposure to subinhibitory concentrations of farnesol decreased the amount of ergosterol extracted from the fungal cells. Furthermore, farnesol also showed lower MIC values when the strains were subjected to osmotic stress, indicating the action of this compound on the fungal membrane. Thus, due to the high in vitro antifungal activity, this work brings perspectives for the performance of in vivo studies to further elucidate the effects of farnesol on the host cells.

Antifungal therapeutics for dimorphic fungal pathogens

“…Unfortunately, some antifungal studies continue to ignore the pathogenic forms and instead limit studies to mycelial-phase cells. [70][71][72] Further complicating antifungal susceptibility profiling are the lack of standardized methods addressing complications for dimorphic fungi. While the CLSI methods for yeasts (M27-A3) 60 work well for Candida and Cryptococcus yeasts, they are inadequate for testing yeast-phase cells of the dimorphic fungal pathogens, which have longer generation times and require higher inocula for efficient and consistent growth in broth culture.…”

In Vitro Antibiofilm Activity of Eucarobustol E against Candida albicans

“…The production of ergosterol in C. albicans was quantified through a spectrophotometric method. Extracted sterols demonstrated a characteristic four-peak spectral absorption pattern at between 240 and 300 nm (41)(42)(43). In our experiment, EE reduced the level of ergosterol production in C. albicans.…”

“…Total cellular ergosterol from the cell cultures was quantified as previously reported (41)(42)(43). Briefly, suspensions of 10 6 cells/ml with or without EE were incubated at 35°C for 12 h under constant shaking at 150 rpm.…”

Endemic Mycoses in Immunocompromised Hosts

“…With the exception of ciprofloxacin and voriconazole against H. capsulatum in yeast form, most tested combinations of ciprofloxacin and antifungal drugs resulted in significant minimum inhibitory concentration (MIC) reductions against both species. The in vitro inhibitory effect of farnesol against C. posadasii in combination with antifungal agents was also recent tested and farnesol was associated with significantly decreases in the MICs for itraconazole and voriconazole and acts synergistically with amphotericin B and caspofungin [43]. Although studies of these combinations in patients are needed, these data highlight the potential for synergistic combination antimicrobial therapy as a promising adjuvant in cases of disseminated or refractory mycoses.…”