Production of crude bacteriocins by selected lactic acid bacteria isolated from some fermented foods

Abstract

Isolation of lactic acid bacteria (LAB) from cheese, pickles, palm wine and yoghurt (fermented foods) were carried out. The LAB were cultivated on De Man Rogosa Sharpe agar and were identified based on their colony and cell morphology, Gram’s staining and biochemical tests. The LAB were screened for potential to produce crude bacteriocins in De Man Rogosa Sharpe (MRS) broth using standard techniques. The efficacy of the crude bacteriocins produced by the LAB were tested against Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Streptococcus pyogenes. Cheese had the highest LAB counts (3.12×10⁷CFU/g) than other fermented foods analysed. The lactic acid bacteria isolates were probably identified as Lactococcus lactis, Lactobacillus bulgaricus, Leuconostoc mesenteroides and Pediococcus halophilus. Out of the twelve (12) LAB screened for bacteriocin production in MRS broth (in test tubes), six (6) tubes revealed the produced bacteriocins. The result of the efficacy of the crude bacteriocins on the test bacteria showed that Escherichia coli and Streptococcus pyogenes had clear zones of inhibition ranging from 9 to 17mm for Escherichia coli and 9 to 16mm for Streptococcus pyogenes while Bacillus cereus and Pseudomonas aeruginosa were completely resistant to the test bacteriocins. The presence LAB in fermented food products and other food products will enhance preservation (shelf life extension) of the products and still maintain their keeping quality.