Abstract
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 > 2.5 > 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.
Highlights
There is substantial concern that pharmaceutical industries are not able to develop novel and effective antibiotics at a rate sufficient to compete with the emergence of microbial resistance to antibiotics used in the clinic
Some examples that were previously reported are delayed antagonism, disc diffusion assay, spot on lawn or agar overlay, well diffusion assay and paper disc methods (Soomro et al, 2007; Macaluso et al, 2016; Balouiri et al, 2016; Oliveira et al, 2017), critical dilution assays (Barbosa et al, 2016), flipstreak method (Lewus and Montville, 1991).The aim of this study was to isolate, evaluate the antimicrobial activity and pH tolerance of lactic acid bacteria (LAB) isolated from locally consumed probiotic food in Nsukka, Enugu State, Nigeria
The isolates are acid tolerant, a property characteristic of probiotic bacteria. These results show that pH tolerance is strain - dependent among Lactobacillus spp
Summary
There is substantial concern that pharmaceutical industries are not able to develop novel and effective antibiotics at a rate sufficient to compete with the emergence of microbial resistance to antibiotics used in the clinic. Interest in the use of probiotic foods with beneficial microorganisms as an alternative to antibiotic therapy has geometrical increased within the past decades. Low pH of lactic acid bacteria (LAB) is essential in their applicability as probiotics. To achieve a high concentration (109 to 1011 CFU/day) and to allow for their beneficial action, LAB must survive the low pH of the gastrointestinal tract (GIT), colonize it and synergistically dislodge pathogenic bacteria via production of defensive metabolites
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