Evaluation of Lactobacillus spp. isolated from locally consumed probiotic food in Nsukka, Enugu State, Nigeria for antimicrobial activity utilizing agar well diffusion and pH tolerance tests

Antimicrobial activity against entero-pathogens and tolerance to acid stress are crucial characters of probiotic bacteria. Lactobacillus spp. isolates were phenotypically characterized using colony observation, catalase test and Gram stain reaction.  The pH (1.5, 2.5 and 3.5) tolerance of each isolate was evaluated at 0 and 4 h. The antibacterial activities of the isolates were tested against pathogenic strains of Bacillus spp., Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium and Staphylococcus aureus. Among the isolates screened, 20 were Gram positive and catalase negative. In an agar well diffusion, isolate O4 resulted in the highest inhibition zone diameter, 13 mm against P. aeruginosa while isolates OK4, UK1, P2, P3 and P4 did not produce any inhibition zones against any of the pathogens tested. Isolate Y1 showed the broadest inhibitory activity against the pathogens tested inhibiting all the pathogens tested except S. typhimurium. The pH tolerability studies showed that the isolates proliferated more at lower acidic pH: 1.5 u003e 2.5 u003e 3.5. Food products containing Ogiri, Ukpaka, Okpeye, Akamu and Yoghurt provides useful sources of probiotic bacteria.   Key words: Antimicrobial activity, Lactobacillus spp, pH tolerance, entero-pathogens.