Retigeric Acid B Enhances the Efficacy of Azoles Combating the Virulence and Biofilm Formation of <i>Candida albicans</i>

Abstract

Candida albicans is one of the most prevalent human opportunistic pathogens. C. albicans undergoes a yeast-to-hyphal transition that has been identified as a virulence factor as well as a critical element for mature biofilm formation. A previous study in our lab showed retigeric acid B (RAB), a lichen derived pentacyclic triterpenoid, displayed synergistic antifungal activity with azoles. We now showed that this combination also proved to be adequate in combating the formation of hyphae in vitro. In vivo tests with mice demonstrated RAB could markedly enhance the efficacy of fluconazole to promote the host's longevity through inhibiting hyphae formation and adherence to host cells. It was also observed that RAB and azoles interacted synergistically to block the formation of biofilm. Our data suggested the attenuated yeast-to-hyphal switch contributed to the defect of mature biofilm formation. Moreover, quantitative real-time polymerase chain reaction (qPCR) analysis showed RAB could reduce the transcript level of MDR1, a multidrug efflux pump, and caused a slight transcriptional reduction for another drug pump related gene CDR1. Taken together, our work provides a potential application to combat candidiasis using the combination of RAB and azoles.Key words hyphae; biofilm; virulence; synergistic; Candida albicans Candida albicans is a dimorphic pathogen which undergoes the transition from yeast form to hyphal form according to the growing condition.1,2) Hyphae filaments have the ability to penetrate tissue and escape immune cell recognition, which results in systemic infection in humans.3) Filamentation is also required for normal biofilm formation and development. 4,5) A biofilm is a protected niche for microorganisms in which they are less susceptible to antibiotic treatment and can create a source of persistent infection. 4,6) The development of C. albicans biofilms is clinically significant since cells within biofilm are more resistant to traditional antifungal agents and host immune factors, making biofilm-associated C. albicans infections much more difficult to treat. 7) A C. albicans biofilm consists of a network of yeasts, pseudohyphae and hyphae encased in a self-produced extracellular matrix. The formation of a biofilm initiates with the adherence of blastopores to a surface. Following adhesion, an extracellular matrix is secreted to encase the community of organisms. 4) During the process, yeast cells differentiate into hyphae, and form a stable structure. Inhibition of the yeast-to-hyphal transition could be used as an effected approach to prevent biofilm formation, as hyphae defective mutants have deficiencies in producing a substantial biofilm. 8)Lichens are a useful source of multiple secondary compounds which exhibit excellent bioactivities such as antibiotic, antifungal, antiviral properties.9,10) Our previous study reported that retigeric acid B (RAB) isolated from the lichen Lobaria kurokawae has a synergistic effect to reduce the minimum inhibitory concentration (MIC) of azoles, especially in...

Efflux pump-mediated resistance to antifungal compounds can be prevented by conjugation with triphenylphosphonium cation

“…The supernatant was aspirated, and non-adherent cells were removed by thoroughly washing with sterile PBS three times. The C. albicans biofilms were then treated with IS-2-Pi-TPP or the same volume of the solvent dimethyl sulfoxide for 24 h. The treated biofilms were stained with FDA and PI for 30 min and washed with PBS three times 69 . The stained samples were observed under an Olympus fluorescence microscope (Olympus IX71, Olympus, Tokyo, Japan).…”

Quinone derivatives isolated from the endolichenic fungus Phialocephala fortinii are Mdr1 modulators that combat azole resistance in Candida albicans

“…The transcriptional expression of CDR1 , CDR2 and MDR1 in the tested C. albicans or C. tropicalis isolates was measured using qPCR as previously reported 55 . The primers used are shown in Supplementary Results Table S6 .…”

Mechanisms of Candida Biofilm Drug Resistance

“…Similarly to the β-lactamase inhibitors used to overcome β-lactam bacterial resistance, drugs active against the biofilm-specific drug resistance mechanisms discussed above may have the potential to eradicate biofilms in combination with other antifungals. Many laboratories have begun to explore this possibility [102,127–134]. The finding that stress responses are involved in Candida biofilm resistance raises the possibility of inhibiting these pathways to potentiate the effects of conventional antifungals.…”