Isolation, Phenotypic Characterization and Functional Analysis of Probiotic Lactic Acid Bacteria from Indigenous Food Products

Abstract

The objective of this research work was to screen some useful probiotic Lactic Acid Bacteria (LAB; n=15) from various indigenous food sources. Preliminary identification based on Gram reaction and catalase test, revealed 60% cocci and 40% bacilli. Antagonistic activity was assessed by agar well diffusion against Bacillus subtilis, Salmonella typhi, Escherichia coli, P. aeruginosa, Staphylococcus aureus, and Candida albicans, showed that the cell-free culture supernatant of LBM1 produced inhibition zones of 37mm (E. coli), 25mm (P. aeruginosa), and 30mm (S. aureus). LCT2 showed 30mm (S. aureus) and 34mm (E. coli), while LCR8 exhibited 40mm (S. typhi) and 38mm (C. albicans). All three strains survived at pH 3 for 3h with counts of 2.1×10⁵, 2.2×10⁵, and 1.8×10⁵ CFU/mL and survival rates of 94%, 96%, and 93%, respectively. Biofilm formation, confirmed by Congo red agar, and microtiter assays, showed OD₆₃₀ values of 0.368±0.05 (LBM1), 0.342±0.17 (LCT2), and 0.233±0.04 (LCR8). Heavy-metal resistance testing revealed that all three strains tolerated nickel nitrate up to 10 ppm, indicating potential resilience under stress conditions. Moreover, production of exopolysaccharides (EPS) was also observed by LBM1, LCT2 and LCR8. The antimicrobial activity of LAB EPS was also assessed for S. aureus, E. coli, S. typhi, and C. albicans. Notably, all these strains exhibited significant antimicrobial activity. These findings highlight the adaptability and potential applications of LAB strains, particularly those with antimicrobial activity, pH resistance, bile salt tolerance and robust EPS production.