Antibacterial potential of an ethnic probiotic containing food, Akhuni/Axone and its chemical characterization

Abstract

‘Akhuni/Axone’, a popular traditional fermented soybean food of northeast India, was evaluated for antibacterial activity against Staphylococcus aureus and Escherichia coli along with its mechanism of action and chemical characterization. The effects of “Akhuni/Axone” treatment on these bacteria were assessed using the following methods: zone of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentrations (MBC), time kill curve analysis, cellular leakage measurement, oxidative stress analysis, EtBr influx/efflux assay and SEM microscopy. Among petroleum ether, ethyl acetate, ethanol and methanol extracts of ‘Akhuni/Axone’, ethyl acetate extract (AKEA) showed significant antibacterial activity against both the pathogens. The MIC of AKEA was found to be 8.09 ± 0.86 mg/ml and 10.79 ± 0.91 mg/ml against S. aureus and E. coli respectively whereas MBC values were 10.79±0.63 mg/ml and 13.45 ± 1.12 mg/ml against S. aureus and E. coli respectively. The time-kill analysis and cellular leakage assay results indicated that AKEA has bactericidal effect in a concentration and time dependent manner towards both the pathogens. Oxidative stress analysis indicated that AKEA treatment led to excessive ROS production and oxidative stress. EtBr influx/efflux assay indicated AKEA as efflux pump inhibitor and SEM microscopy confirmed the morphological changes on the cell wall and cytoplasmic membrane of bacteria. The chemical analysis of AKEA through 1H NMR, 13C NMR and GC-MS showed a high abundance of triglycerides. These findings indicate that ‘Akhuni/Axone’ can inhibit bacteria, S aureus and E coli and results from this study will be helpful in further studies on other antimicrobial compounds and for developing food-based natural preservatives.