Effects of PH and Storage Temperatures on Antibacterial Activity of Bacteriocin Produced by Lactic Acid Bacteria Isolated from OGI

Abstract

Aims: Lactic acid bacteria are important organisms recognized for their fermentative ability. They produce various compounds including bacteriocins which are proteinaceous antimicrobial compounds. The purpose of this study was to evaluate the lactic acid bacterial content of ogi, extract crude bacteriocin from the lactic acid bacterial isolate(s) and determine the effects of pH and storage temperature on the antimicrobial properties of the crude bacteriocin extract. Study Design: The study was designed to isolate and characterise lactic acid bacteria from ogi, thereafter extract crude bacteriocins from the isolates and then determine the antibacterial activities of the bacteriocins so extracted against some known indicator organisms. Place and Duration of Study: Ogi samples were purchased from vendors who hawk it around the Benson Idahosa University campus and the study was done at the Department of Basic Sciences, Faculty of Basic and Applied Sciences, Benson Idahosa University, Benin City, Nigeria; between October 2012 and June 2013. Methodology: Preliminary isolation and characterization of lactic acid bacteria was done using standard microbiological methods after which the bacteriocins were extracted by propagating in 500ml MRS broth (pH 7.0 glucose 0.25% w/v) and incubated for 72 h at 30ºC under anaerobic conditions. Extract was obtain by centrifuging cultures at 10,000 rpm for 20 min. Antimicrobial activity of the extract was determined using agar well diffusion method. Indicator organisms utilized were; Escherichia coli and Staphylococcus aureus. The effects of pH and storage temperatures of the crude bacteriocin, on the antimicrobial properties were determined using standard methods. Results: Lactobacillus plantarum, Lactobacillus casei, Lactobacillus brevis, Lactobacillus fermentum and Lactobacillus jensenii were the lactic acid bacteria species isolated and identified from the Ogi samples. Lactobacillus plantarum had the highest zone of inhibition during the screening test for antibacterial activity and was used to produce the bacteriocins used for the subsequent tests. At pH 2, there was a high antimicrobial activity but at pH 10, there was no antimicrobial activity. Crude bacteriocin extract stored at -20ºC also showed the highest antimicrobial activity. Conclusion: This study has established that Ogi is a viable source of several lactobacilli which are capable of producing several antimicrobial compounds such as bacteriocins. It also established that bacteriocins recovered from Lactobacillus plantarum have a potent antimicrobial activity against a variety of both diarrhoeagenic and spoilage bacterial.