Antimicrobial Activities and Characterization of Bacteriocin-Like Substances Isolated from Lactic Acid Bacteria of Local Fermented Foods

Abstract

Bacteriocins produced by a number of lactic acid bacteria (LAB) comprise a variety of antimicrobial proteins that may be used as antibiotic alternative in food preservation. The present study aimed to isolate and characterize LAB-derived bacteriocin-like substances (BLS) from local fermented foods. A total of twenty-one bacterial strains were isolated and subjected to an antibacterial assay. Five isolates designated as AB1, AB2, AK1, AK2, AnK1 showed inhibitory activity against selected indicator organisms and were subjected to further characterization. Upon BLAST analysis of the 16S rRNA gene sequences, the isolates showed close relationship to Lactobacillus plantarum with similarity ranging from 91 to 97%. Moreover, the antibacterial metabolite production of the isolates was observed to peak on the 5th to 7th day of incubation. Since AnK1 showed the highest zone of inhibition among 5 isolates, it was selected for characterization of the BLS isolated by ammonium sulfate precipitation and anion exchange chromatography. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the AnK1-BLS had a single band and a molecular weight around 15 kDa, and a total protein concentration of 7.06 µg/mL. Interestingly, AnK1-BLS had a broad antimicrobial spectrum on both gram-negative and gram-positive food-borne pathogens, including Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa, and Bacillus subtilis. Moreover, the purified AnK1-BLS exhibited good thermal stability when heated at 80‒121°C. Likewise, its inhibitory activity was not affected by pH in the range of 3.0 to 6.5, with maximum activity recorded at pH 3.0. The results suggest that AnK1-BLS may have application prospects in the food industry. Further studies on the complete protein characterization of AnK1-BLS is recommended to fully harness its capabilities.