Antimicrobial activities and bacteriocins of lactic acid bacteria isolated from Nigeria indigenous fermented cowmilk “nunu”

Nunu is a nutritious fermented yoghurt-like milk beverage that can serve as a source of lactic acid bacteria (LAB) with antimicrobial and bacteriocin potentials. Nunu samples were screened for LAB with antimicrobial activity against test organisms. Three LAB, namely Lactobacillus parafarraginis OCLP1, L. fermentum CSL58 and L. buchneri MZE12 out of a total of 14 isolates produced antimicrobial activity against Bacillus anthracis CHF-2011-32b, B. cereus DHM5-1, Providencia vermicola KSVDL-09-71600, P. rettgeri SIRT3, P. stuartti SILT11 and other test organisms. Antimicrobial factors were assayed in LAB cell-free extracts (CFE), neutralized CFE, and ammonium sulphate precipitants of the CFE, and Lactobacillus parafarraginis OCLP1 demonstrated highest activity with zone of inhibition = 20.33±3.51 mm­, 13.33±1.09 mm and 25.33±2.52 mm respectively. The CFE of the LAB especially L. parafarraginis OCLP1 demonstrated wide activity spectra by inhibiting both the gram-positive and gram-negative bacteria tested. Result of plasmid curing of the LAB indicate that the bacteriocins of L. parafarraginis OCLP1 was plasmid-encoded while the others have their gene clusters on the chromosome. This study concluded that bacteriocin-producing LAB can be found in “nunu” and recommend the use of the isolated LAB as starter in fermented food production after ensuring their safety through toxicological studies.