Isolation and characterization of lactic acid bacteria from wheat and fenugreek and evaluation of their antifungal and antibacterial activities

Résumé

Introduction: Lactic acid bacteria (LAB) constitute a major group of probiotic microorganisms recognized for their ability to inhibit pathogenic microbes, modulate the microbiota, and enhance host protection through the production of organic acids, antimicrobial compounds, and other bioactive metabolites.

Methods: The aim of this study was to isolate and characterize lactic acid bacteria from wheat and fenugreek seeds and to evaluate their antibacterial and antifungal activities for potential probiotic and biocontrol applications. Eight LAB strains isolated from wheat and fenugreek seeds were characterized morphologically, biochemically, and functionally, and subsequently assessed for their antibacterial and antifungal potential.

Results: Macroscopic and microscopic observations showed that all strains were Gram-positive, primarily cocci and rods, devoid of DNase activity, and capable of producing biofilm, suggesting profiles compatible with probiotic use. Antibacterial activity varied depending on both the LAB strain and the target pathogen. Inhibition zones ranged from 0 to 15 mm against Staphylococcus aureus (0–10 mm), Escherichia coli (6–11 mm), Listeria monocytogenes (0–15 mm), Bacillus cereus (0–11 mm), Micrococcus luteus (0–11 mm), and Salmonella typhimurium (0–7 mm). Activity was attributed to medium acidification and the production of antimicrobial metabolites, including organic acids and bacteriocins. Selective antifungal activity was also observed, with inhibition zones ranging from 0 to 27 mm against Candida albicans (0–20 mm), Candida krusei (0–22 mm), Candida neoformans (0–26 mm), Aspergillus brasiliensis (0–25 mm), and Aspergillus fumigatus (0–27 mm). These results reflect strain–target-specific interactions and confirm the potential of the LAB strains to inhibit opportunistic yeasts and molds of sanitary relevance.

Conclusion: Overall, these findings quantitatively demonstrate the biotechnological potential of LAB strains derived from wheat and fenugreek seeds as biocontrol agents and probiotic candidates for the prevention of foodborne infections and reduction of fungal contamination.