Bacteriocin Screening of North East Indian Fermented Foods

Previously isolated bacterial isolates from various fermented foods of North East India was evaluated for bacteriocin production by agar well diffusion method (Li et al., 2015 (link)). Cells were grown in MRS for 16–18 h and then centrifuged at 8000 rpm, 4°C for 15 min to remove the cells. The supernatant was neutralized to the pH of 7.0 with 0.1 N NaOH followed by filter-sterilization through 0.2 μm membrane. Consequently agar well diffusion assay was performed against indicator strain K. rhizophila. Briefly, 50 μL of cell free supernatants were placed into 6 mm wells on BHI agar plates seeded with the above indicator strains. After incubation at 37°C for 12 h, the diameters of inhibition zones were measured. Proteinaceous nature of antibacterial substance was checked by incubating the cell-free supernatant (CFS) with 1 mg/ml of proteinase K (Hi Media) at 37°C for 2 h (Devi and Halami, 2011 (link)). Both protease-treated CFS were assayed for activity as indicated above (Devi and Halami, 2011 (link)). CFS was also tested for heat resistance at boiling temperature for 15 min (Sure et al., 2016 ).