Screening of Antimicrobial Factors of BK3 Isolate from an Indigenous Fermented Food Product (Burong Kanin)

Abstract

Twenty-eight strains of lactic acid bacteria from five fermented food samples namely: “burong kanin” (BK), “burong isda” (BI), “balao-balao” (BB), “longganisa” from Ilocos region (LI), and “longganisa” from Cavite (LC) were screened and tested for antimicrobial activity using the agar well diffusion assay method and Lactobacillus plantarum NCDO 955 as indicator microorganism. Strain 3 isolated from “burong kanin” (BK3) exhibited the highest antimicrobial activity. BK3 isolate strain grew best in de Man, Rogosa, and Sharpe (MRS) medium than in Tryptone Glucose Yeast Extract (TGYE) medium. Two samples (crude and semi-purified extracts) were used in the elucidation of antimicrobial factors: organic acids, enzymes, hydrogen peroxides and bacteriocins. | The semi-purified sample was prepared by pH-mediated adsorption desorption method followed by dialysis, high-speed centrifugation and lyophilization (freeze-drying). Antagonistic activity from the crude sample manifested inhibitory effects due to production of lactic acids, and probably due to peroxides and enzymes. On the other hand, the semi-purified or freeze-dried sample showed inhibitory effects on the growth of Lactobacillus brevis, Lactobacillus lactis subsp. lactis and Lactobacillus plantarum NCDO 955 which was suggestive of bacteriocin activity. The zone of inhibition was largest at pH 2. The antimicrobial activity of BK3 isolate at neutral pH was probably an indication of bacteriocin action. Bactericidal activity was lost at high pH values especially when high pH values were combined with an elevated temperature. BK3 isolate was not affected by amylases but was destroyed by exposure to a proteolytic enzyme. The BK3 strain from “burong kanin” was found to be Gram-positive which inhibited the growth of Lactobacillus lactis while no inhibition was observed against Escherichia coli.