Anti-Candida activity of two-peptide bacteriocins, plantaricins (Pln E/F and J/K) and their mode of action

• Fungicidal activity of plantaricin peptides was reported against C. albicans.
• Increased ROS production was identified as the main cause of apoptosis.
• However, killing by PlnJ was also associated with increased membrane permeability.
• These peptides may be exploited in the development of bioactive compounds.

The fungicidal effect of plantaricin peptides PlnE, -F, -J, and -K was studied against pathogenic yeast, Candida albicans. Dose-dependent inhibitory effect was observed by drop in cell viability, further demonstrated by measuring the fluorescence intensity of cells by exposing them to 5, (6)-carboxyfluorescein diacetate (CFDA). Live/dead staining by CFDA and propidium iodide (PI) also suggested the viability loss response. Also, the PI uptake by treated cells suggested the membrane damage. PlnJ was identified as most inhibitory among different plantaricins tested. PlnJ not only induced membrane potential dissipation but also resulted in the release of K+. In addition, enhanced production of reactive oxygen species (ROS) was also observed by fluorometry using 2′,7′-Dichlorodihydrofluorescein diacetate (DCFH-DA). Dual staining with Hoechst stain and PI depicted both early apoptotic and necrotic cells in the treated population. Terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) positive staining further confirmed the ROS-mediated apoptosis. Scanning electron microscopy and transmission electron microscopy also revealed characteristic apoptotic features such as appearance of blebs, indentations, and wrinkling of the cell wall, discontinuity of cell membrane, undefined and damaged nuclei, and shrinkage of protoplasm. Taken together the results suggest that Pln-treatment initiate the apoptosis cell death which may lead to necrosis due to toxicity of the plantaricin peptides.