Antifungal Activity of Human Cathelicidin LL-37, a Membrane Disrupting Peptide, by Triggering Oxidative Stress and Cell Cycle Arrest in <i>Candida auris</i>

Abstract

Candida auris, an evolving multidrug-resistant pathogenic yeast, is known for causing severe invasive infections associated with high mortality rates in hospitalized individuals. Distinct from other Candida species, C. auris can persist for longer periods on different surfaces and is resistant to all of the major classes of antifungal drugs. Therefore, there is an urgent need for new antimycotic drugs with improved efficacy and reduced toxicity. The development of new antifungals based on antimicrobial peptides from various sources is considered a promising alternative. In this study, we examined the in vitro anti-yeast activity of the human cathelicidin peptides LL-37 against clinical strains of C. auris alone and in combination with different antifungal drugs by broth microdilution assay. To understand the antifungal mechanism of action, cell envelopes, cell cycle arrest, and effect on oxidative stress enzymes were studied using standard protocols. The minimum inhibitory and fungicidal concentrations of cathelicidin LL-37 ranged from 25–100 and 50–200 µg/mL, respectively. A combination interaction in a 1:1 ratio (cathelicidin LL-37: antifungal drug) resulted in 70% synergy with fluconazole and 100% synergy with amphotericin B and caspofungin. Assessment of the C. auris membrane by using propidium iodide assay after exposure to cathelicidin LL-37 linked membrane permeabilization with inhibition of C. auris cell growth and viability. These results were backed up by scanning electron microscopy studies demonstrating that exposure with cathelicidin LL-37 caused C. auris cells to undergo extensive surface changes. Spectrophotometric analysis revealed that cathelicidin LL-37 caused oxidative stress in C. auris, as is evident from the significant increase in the activity of primary antioxidant enzymes. In addition, cathelicidin LL-37 inhibited the cell cycle and accumulated cells in the S phase. Therefore, these results specify the potential of cathelicidin LL-37 for developing a new and effective anti-Candida agent.

Keywords

• <i>Candida auris</i>
• infection
• cathelicidin LL-37
• cell cycle arrest
• combination therapeutics