Purification and characterization of two bacteriocins from Lactobacillus brevis BK11 and Enterococcus faecalis BK61 showing anti-Helicobacter pylori activity

The aim of this study was to investigate the antimicrobial effects of purified bacteriocins isolated from Lactobacillus brevis BK11 and Enterococcus faecalis BK61 on Helicobacter pylori. After the final purification step, the molecular weights of the purified bacteriocins from L. brevis BK11 and E. faecalis BK61 were estimated to be approximately 6.5 and 4.5 kDa, respectively. Significant decrease in the antimicrobial activity of these bacteriocins was observed when they were treated with several proteolytic enzymes. However, their antimicrobial activity was stable over long periods of storage and a wide range of pH and was relatively heat resistant. The inhibitory spectrum of the bacteriocin produced by L. brevis BK11 strain was quite narrow, whereas the bacteriocin produced from E. faecalis BK61 strain exhibited a broad antimicrobial spectrum against various foodborne pathogens such as Listeria monocytogenes, Escherichia coli O157, and Salmonella enteritidis. Treatment of H. pylori with these bacteriocins significantly reduced the number of cells of the pathogen found adhering to the monolayers of cultured human gastric adenocarcinoma epithelial cell line (p < 0.05). Furthermore, the urease activity of adherent H. pylori after treatment with the bacteriocins was lower than that for the control group, but there appeared to be no significant difference between the competition and displacement groups (p > 0.05).