Synergistic Activity of the Tyrocidines, Antimicrobial Cyclodecapeptides from Bacillus aneurinolyticus, with Amphotericin B and Caspofungin against Candida albicans Biofilms

Abstract

dTyrocidines are cationic cyclodecapeptides from Bacillus aneurinolyticus that are characterized by potent antibacterial and antimalarial activities. In this study, we show that various tyrocidines have significant activity against planktonic Candida albicans in the low-micromolar range. These tyrocidines also prevented C. albicans biofilm formation in vitro. Studies with the membrane-impermeable dye propidium iodide showed that the tyrocidines disrupt the membrane integrity of mature C. albicans biofilm cells. This membrane activity correlated with the permeabilization and rapid lysis of model fungal membranes containing phosphatidylcholine and ergosterol (70:30 ratio) induced by the tyrocidines. The tyrocidines exhibited pronounced synergistic biofilm-eradicating activity in combination with two key antifungal drugs, amphotericin B and caspofungin. Using a Caenorhabditis elegans infection model, we found that tyrocidine A potentiated the activity of caspofungin. Therefore, tyrocidines are promising candidates for further research as antifungal drugs and as agents for combinatorial treatment.

Inhibition of agronomically relevant fungal phytopathogens by tyrocidines, cyclic antimicrobial peptides isolated from Bacillus aneurinolyticus

“…TrcA and B treatment of F. solani led to similar dye uptake (results not shown). Similar results on the permeabilization activity of the tyrocidines were recently found by Troskie et al (2014) with Can. albicans biofilm cells as target.…”

Antifungal membranolytic activity of the tyrocidines against filamentous plant fungi

“…It is also possible that there is differential binding to the different lipids in the ergosterolsphingolipid rafts with Trp-containing peptides forming oligomers and lytic structures, possibly pores, while the Phe-containing peptides bind to the GlcCer without forming lytic oligomers. Binding the GlcCer could have downstream effects on the fungal pathogen, particularly as it has been found that TrcA leads to ROS, as well as membrane permeabilisation in C. albicans [8]. ROS generation has been related to interaction of some plant defensins with sphingolipids, specifically GlcCer in fungal membranes [15,16].…”

“…However, this broad activity also entails haemolytic and cytolytic activity [6,9,10]. This toxicity was overcome by utilising synergistic combinations such as TrcA at sub-haemolytic concentrations with caspofungin that inhibits fungal b-(1,3)-glucan synthase [8,11]. Synergistic anti-biofilm activity and in vivo activity was observed for this two-peptide combination against C. albicans in a Caenorhabditis elegans infection model [8].…”

“…The tyrocidines were also found to be active against the pathogenic yeast Candida albicans [7,8], with tyrocidine A (TrcA) being synergistic with the membrane active antifungal drug, amphotericin B, in the eradication of mature C. albicans biofilms [8]. However, this broad activity also entails haemolytic and cytolytic activity [6,9,10].…”

“…This toxicity was overcome by utilising synergistic combinations such as TrcA at sub-haemolytic concentrations with caspofungin that inhibits fungal b-(1,3)-glucan synthase [8,11]. Synergistic anti-biofilm activity and in vivo activity was observed for this two-peptide combination against C. albicans in a Caenorhabditis elegans infection model [8]. Furthermore, regardless of the lytic toxicity of the tyrocidines, tyrothricin comprising of about 50e60% tyrocidines, has been in use for more than 70 years as a broad spectrum topical antibiotic in clinical applications [12].…”