Bacteriocin production by Lactococcus sp. strain KA45 isolated from locally fermented foods for food preservation

Natural antimicrobial compounds from lactic acid bacteria (LAB) have received increasing attention as alternatives to synthetic food preservatives. However, limited studies have explored bacteriocin-producing LAB from Nigerian fermented foods and their potential application in food preservation. In this study, LAB were isolated from Nigerian traditional fermented foods (kunun-zaki, kunun-aya, wara, nono, and daddawa) using De Man, Rogosa and Sharpe (MRS) agar, and screened for antimicrobial activity against selected food spoilage and pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Bacillus subtilis) using the agar well diffusion method. Among the fifty isolates obtained, strain KA45 exhibited the highest antimicrobial activity and was identified by 16S rRNA gene sequencing as Lactococcus sp., showing 96.61% sequence similarity with Lactococcus garvieae. Optimization of bacteriocin production using response surface methodology revealed maximum activity at pH 5.28, 20 °C, and 72 h incubation. The antimicrobial peptide, designated Bac-G, was partially purified using ammonium sulphate precipitation and gel filtration chromatography, resulting in an increase in specific activity to 12.7 AU mg^-1. Bac-G exhibited stability across a broad pH range and moderate temperatures. Toxicological evaluation in albino rats (up to 5000 mg kg^-1 body weight) revealed no mortality or significant physiological abnormalities. Application of Bac-G (10-15% v/v) significantly reduced microbial growth in traditional Nigerian foods (akamu and masa) during storage and improved sensory acceptability compared with untreated controls. These findings highlight the potential of bacteriocin produced by Lactococcus sp. strain KA45 as a natural bio-preservative for improving the microbiological safety and shelf life of fermented food products.