Isolation and characterization of antimicrobial proteins produced by a potential probiotic strain of humanLactobacillus rhamnosus231 and its effect on selected human pathogens and food spoilage organisms

Abstract

Objective : To study in vitro properties of potential probiotics and the antimicrobial activity of Lactobacillus rhamnosus 231 isolated from human faeces. Methods and Results : Lact. rhamnosus 231 isolated from human faeces tolerated bile salt (4%), phenol (0.5%), and NaCl (4%) and retained viability at low pH (2.5). The cell-free culture (CFC) fi ltrate and extracellular protein concentrate (EPC) of Lact. rhamnosus 231 contained antimicrobial substances active against Pseudomonas aeruginosa, Escherichia coli, Enterobacter aerogenes , Staphylococcus aureus, Salmonella spp., Helicobacter pylori , Campylobacter jejuni, Bacillus cereus, Bacillus megaterium , and Listeria monocytogenes . EPC contained a mixture of low molecular weight antimicrobial proteins, produced during log and stationary phases of growth against the test organisms. Thermostability of the antimicrobial proteins and their sensitivity to proteinase K was observed to be test organism specifi c. The antimicrobial activity was observed in the pH range 4.5–9 except against Ps. aeruginosa and Ent. aerogenes . These antimicrobial proteins are low molecular weight (4 kDa) anionic peptides as determined by tricine-SDS-PAGE and 2D gel. Periodic acid-Schiff’s (PAS) staining of gel confirmed the presence of carbohydrate moiety with low molecular weight peptides. The antimicrobial activity of the partially purifi ed protein was determined against Staph. aureus 74B, H. pylori 33, H. pylori 17874, and C. jejuni CJE 33566. Conclusion: Human Lact. rhamnosus 231 exhibits in vitro properties of potential probiotic. CFC fi ltrate and EPC of Lact. rhamnosus 231 exhibit antimicrobial activity against potential human pathogens and food spoilage organisms. Antimicrobial proteins in EPC were partially purified and characterized. In vitro properties of potential probiotic and antimicrobial properties of Lact. rhamnosus 231 could be useful as food additive against human pathogens and removal of food contaminants in the target environment. Key words: Antimicrobial proteins, anti-Helicobacter activity, cell-free culture (CFC) fi ltrate, Lactobacillus rhamnosus 231, potential probiotic