Screening, Identification and Antibiotic Susceptibility Pattern of Bacteriocin-producing Lactic Acid Bacteria Isolated from Selected Traditionally Fermented Products

Abstract

Aims: To isolate and identify bacteriocin-producing lactic acid bacteria from traditionally fermented products and determine their antibiotic susceptibility pattern. Place and Duration of Study: Department of Microbiology, Federal University of Technology, Akure, Nigeria between October, 2012 – March, 2013. Methodology: Lactic acid bacteria (LAB) isolates from samples of traditionally fermented products (“burukutu”, “pito”, yoghurt, “wara” and “iru”) were screened for bacteriocin production. Bacteriocin screening was performed both by the agar spot test and well diffusion assay. Four reference strains (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853) were used as indicator strains to check sensitivity to the antimicrobial substances produced by the LAB isolates. Carbohydrate fermentation profiles of selected bacteriocin-producing LAB strains were determined using API 50CH kits to identify them up to the species level. Antibiogram of LAB isolates were determined by antibiotic sensitivity discs. Results: A total of sixty-three (63) lactic acid bacteria (LAB) strains obtained from the fermented products were screened for bacteriocin production. Thirty-seven isolates (59%) of these LAB strains showed antimicrobial activity against two or more of the reference varieties used as indicator strains (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853). After excluding inhibition due to organic acids and hydrogen peroxide from the cell-free culture supernatants of these 37 LAB isolates, only 6 (16%) of the 37 selected LAB isolates (10% of the 63 initial LAB isolates) continued to show antimicrobial activity against three of the reference strains. The inhibitory effects of these six (6) LAB strains showed the presence of bacteriocins, hence potent bacteriocin producers. The selected bacteriocin-producing LAB strains (BE1, BO2, IO1, PO4, PO9 and YO7) were identified as Lactobacillus cellobiosus, Lactobacillus brevis, Pediococcus pentosaceus, Lactobacillus rhamnosus, Tetragenococcus halophilus, and Lactobacillus fermentum respectively. All the bacteriocin-producing LAB isolates were susceptible to erythromycin and zinnacef but were resistant to streptomycin and pefloxacin. Conclusion: These results reveal six LAB isolates from traditional fermented products that were capable of producing bacteriocins which could have a potential for food applications as biopreservatives.