Lactic Acid Bacteria Isolated from Humans and Fermented Food Sources with Probiotic Potentials

Abstract

Lactic acid bacteria (LAB) obtained from natural sources may provide strains with useful probiotic properties. This study characterised LAB isolated from Nigerian fermented foods and healthy human sources and evaluated their probiotic potential. A total of 124 presumptive LAB isolates were screened for survival under simulated gastrointestinal conditions, including acidic pH and bile salts. Surviving isolates were assessed for antimicrobial activity against Escherichia coli ATCC 10536, Salmonella Typhimurium ATCC 51812, Listeria monocytogenes ATCC 13932, and Shigella flexneri ATCC 9199, and selected isolates were examined in competitive co-culture assays. Thirty-four isolates were identified within the family Lactobacillaceae. Approximately 80% viability (5 log10 CFU/mL) was observed among selected isolates after 12 h exposure to simulated gastric juice at pH 2 and 2% bile salts. Antimicrobial activity varied among isolates, with zones of inhibition reaching 70 mm in the overlay assay. Isolate 3ST2 (L. casei) showed the strongest overall antagonistic activity, producing a 70 ± 0.00 mm zone of inhibition against all four indicator bacteria. Treated cell-free supernatants generally showed lower antimicrobial activity than live cultures. Competitive co-culture assays also showed variable interactions between LAB isolates and the indicator bacteria. These findings indicate that the fermented foods and human sources examined contained LAB strains with in vitro probiotic potential that warrant further evaluation.