Anti- Candida activity of spent culture filtrate of Lactobacillus plantarum strain LR/14

Summary Objectives This study was undertaken to understand the effect of antimicrobial compounds produced by an environmental isolate of lactic acid bacterium, Lactobacillus plantarum strain LR/14, on growth, viability and biofilm forming ability of the pathogenic yeast, Candida albicans SC5314 and to identify the mode of action of such compounds. Material and methods L. plantarum LR14 was grown at 37 °C for 18 h in MRS broth. The spent culture filtrate (SCF) was collected by centrifugation and checked for anti- Candida activity. Live/dead staining followed by fluorescence microscopy was done to study the membrane damage. Increased membrane permeability was confirmed by measuring the release of ions and macromolecules (ATP) using atomic absorption spectrophotometer and luminometer, respectively. Effect on biofilm formation was quantified by MTT reduction assay. Results The viability of yeast cells was affected by SCF LR14 treatment in a dose-dependent manner, exerting a fungicidal effect. The active compound was identified as a pH-dependent thermostable proteinaceous metabolite. The fungicidal activity was further confirmed by PI staining, suggesting compromised membrane as the cause of cell death. Leakage of intracellular contents such as, K + ions and ATP, as a cause of its inhibitory action further confirmed the membrane disruption. Moreover, significant reduction in biofilm formation was also confirmed. Conclusions SCF LR14 showed potent anti- Candida activity, affecting cell viability, membrane permeability, and biofilm formation and leading to cell death, thereby suggested a probable candidate as a natural therapeutic agent.