ABSTRACT

In this study, lactic acid bacteria were isolated from naturally fermenting food products (Ogi, Ogiri and Ugba). They were screened for their ability to produce bacteriocins and inhibit the growth oftwo food-borne pathogenic test organisms (Staphylococcus aureus and Escherichia coli). The predominant species isolated were Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus casei and Lactobacillus brevis. Bacteriocins was extracted from the four predominant strains which inhibited the growth of the two test organisms. The antimicrobial activities of the isolated LAB strains were screened with varying temperature levels of 30°C, 40°C, 50°C, 80°C and 121°C and the inhibition zones ranged from 0-14mm, of which Lactobacillus plantarum had the highest inhibition zone (14 mm) against Staphylococcus aureus at 40°C after 48 hours ofincubation while Lactobacillus casei had the lowest inhibition zone (8 mm) against Escherichia coli at 80°c after 48 hours of incubation. There was no zone of inhibition at 121°C for any ofthe LAB isolates, this indicates that the bacteriocin extract loses its antimicrobial potentials at 121°C. The same trend was observed for the inhibitory effect ofthese isolated LAB strains after screening with varying pH ranges of2, 4, 6, 8 and 10 respectively and the resulting inhibition zones ranged from 0-12mm, with L. plantarum having the highest inhibition zone of 12 mm against S. aureus at pH 2, while L. casei had the lowest zone of inhibition (0 mm) against E.coli at pH 8. There was no zone of inhibition at pH 10 except for L. plantarum which had just 1 mm zone ofinhibition against S. aureus, indicating that very high acidic pH level is mandatory for bacteriocin to exhibit antimicrobial activities. The Gram-negative test organism (E. coli) had more resistance to the bacteriocin extract than the Gram-positive test organism (S', aureus). Behavior of bacteriocin produced by isolated strains in this study was considered bacteriocidal.