Characterization and Antibacterial Potential of Lactic Acid Bacterium 4I1 Isolated from Freshwater Fish .

This study was undertaken to characterize a lactic acid bacterium 4I1, isolated from the freshwater fish, . Morphological, biochemical, and molecular characterization of 4I1 revealed it to be 4I1. The cell free supernatant (CFS) of 4I1 exhibited significant ( < 0.05) antibacterial effects (inhibition zone diameters: 16.5-20.4 mm) against tested foodborne pathogenic bacteria with MIC and MBC values of 250-500 and 500-1,000 μg/mL, respectively. Further, antibacterial action of CFS of 4I1 against two selected bacteria KCTC-1621 and O157:H7 was determined in subsequent assays. The CFS of 4I1 revealed its antibacterial action against KCTC-1621 and O157:H7 on membrane integrity as confirmed by a reduction in cell viability, increased potassium ion release (900 and 800 mmol/L), reduced absorption at 260-nm (3.99 and 3.77 OD), and increased relative electrical conductivity (9.9 and 9.7%), respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of the CFS of 4I1 resulted in the identification of seven major compounds, which included amino acids, fatty acids and organic acids. Scanning electron microscopic-based morphological analysis further confirmed the antibacterial effect of CFS of 4I1 against KCTC-1621 and O157:H7. In addition, the CFS of 4I1 displayed potent inhibitory effects on biofilms formation by KCTC-1621 and O157:H7. The study indicates the CFS of 4I1 offers an alternative means of controlling foodborne pathogens.