Activity and mechanism of action of antimicrobial peptide ACPs against Candida albicans.

AIMS: Candida albicans is the most prevalent pathogenic fungus, exhibiting escalating multidrug resistance (MDR). Antimicrobial peptides (AMPs) represent promising candidates for addressing this issue. In this research, five antimicrobial peptides, ACP1 to ACP5 which named ACPs were studied as alternative fungicidal molecules. MAIN METHODS: CD assay was used to analyze the 2D structures, Absorbance method was used to test the antimicrobial activity, haemolytic activity, time-kill kinetics, biofilm inhibition and reduction activity, resistance induction activity and assessment against fluconazole-resistant C. albicans. SEM, TEM, CLSM, flow cytometer and FM were carried out to provide insight into the mechanisms of anti-Candida action. KEY FINDINGS: ACPs possessed an α-helical structure and strong anti-Candida activities, with minimum inhibitory concentrations (MICs) from 3.9 to 15.6 µg/mL. In addition, ACPs did not produce hemolysis at concentrations lower than 10 or 62 × MIC, indicating their low cytotoxicity. Fungicidal kinetics showed that they completely killed C. albicans within 8 h at 2 to 4 × MIC. Notably, ACPs were highly fungicidal against fluconazole-resistant C. albicans and showed low resistance. In addition, they were effective in inhibiting mycelium and biofilm formation. Fluorescence microscopy revealed that while fluconazole had minimal to no inhibitory effect on biofilm-forming cells, ACPs induced apoptosis in all of them. The research on mechanism of action revealed that ACPs disrupted the cell membranes, with ROS increasing and cellular mitochondrial membrane potential decreasing. SIGNIFICANCE: ACPs could be promising candidates for combating fluconazole-resistant C. albicans infections.

Studies on the in vitro mechanism and in vivo therapeutic effect of the antimicrobial peptide ACP5 against Trichophyton mentagrophytes.

Trichophyton mentagrophytes is a zoophilic dermatophyte that can cause dermatophytosis in humans and animals. Antimicrobial peptides (AMPs) are considered as a promising agent to overcome the drug-resistance of T. mentagrophytes. Our findings suggest that cationic antimicrobial peptide (ACP5) not only possesses stronger activity against T. mentagrophytes than fluconazole, but also shows lower toxicity to L929 mouse fibroblast cells than terbinafine. Notably, its resistance development rate after resistance induction was lower than terbinafine. The present study aimed to evaluate the fungicidal mechanism of ACP5 in vitro and its potential to treat dermatophyte infections in vivo. ACP5 at 1 ×MIC completely inhibited T. mentagrophytes spore germination in vitro. ACP5 severely disrupts the mycelial morphology, leading to mycelial rupture. Mechanistically, ACP5 induces excessive ROS production, damaging the integrity of the cell membrane and decreasing the mitochondrial membrane potential, causing irreversible damage in T. mentagrophytes. Furthermore, 1% ACP5 showed similar efficacy to the commercially available drug 1% terbinafine in a guinea pig dermatophytosis model, and the complete eradication of T. mentagrophytes from the skin by ACP5 was verified by tissue section observation. These results indicate that ACP5 is a promising candidate for the development of new agent to combat dermatophyte resistance.