Development, functional profiling, and probiotic evaluation of indigenous LAB from Nigerian fermented foods: Antimicrobial mechanisms, in vivo validation, and applications in food preservation and mycotoxin risk reduction.

Indigenous fermented foods are rich sources of functionally diverse lactic acid bacteria (LAB) and associated microorganisms with relevance to food safety, health promotion and sustainable bioprocessing. This study aimed to evaluate the probiotic potential of bacterial isolates recovered from selected Nigerian fermented foods. Bacterial isolates were molecularly identified by 16S rRNA gene sequencing and evaluated for probiotic attributes, including stress tolerance, safety, antimicrobial activity and functional bioactivity. Selected strains were further validated in vivo using Drosophila melanogaster. The isolates included classical LAB (Lactobacillus fermentum PZ070868, Lactococcus lactis PZ070869 and Weissella confusa PZ070870) as well as non-LAB species such as (Lysinibacillus fusiformis PZ070871 and Priestia flexa PZ070873) which were serendipitously identified, likely reflecting the diverse microbial ecology of foods, while Enterococcus gallinarum (PZ070872), phylogenetically related to LAB, was assessed separately due to safety considerations. The isolates exhibited strain-dependent antibacterial and antifungal activities against foodborne and pathogenic microorganisms, presented as mean ± SD (n = 5, mm), with statistically significant differences among strains (p < 0.05). Notably, cell-free supernatants of P. flexa (32.00 ± 1.58) and L. fermentum (30.40 ± 0.89) showed the highest inhibition against Aspergillus fumigatus, demonstrating antifungal activity with potential implications for reducing mycotoxin risk. Moderate antifungal efficacy against Candida albicans, Fusarium solani, Aspergillus flavus and F. solani was observed with E. gallinarum (23.20 ± 1.30), L. fusiformis (21.60 ± 1.14), P. flexa (17.80 ± 1.30) and W. confusa (20.40 ± 1.14), while W. confusa and L. lactis exhibited more selective inhibition. Antibacterial activity for L. fermentum (17.4 ± 2.3) showed the highest inhibition against Klebsiella pneumoniae, L. lactis (16.0 ± 1.0) against Staphylococcus aureus and E. gallinarum (15.8 ± 1.9) against Proteus mirabilis, with moderate inhibition observed against Pseudomonas aeruginosa, Escherichia coli, Salmonella typhi and Listeria monocytogenes. In vivo validation further supported the biological relevance of these findings, with L. fermentum and W. confusa providing notable host protection. Beyond health functionality, L. fermentum (PZ070868) extended the shelf life of zobo beverage by 17-21 days, demonstrating potential as natural biopreservatives. Collectively, this study integrates probiotic screening, antimicrobial and antifungal activity, in vivo validation and food preservation, the study investigates microbial isolates from fermented foods, including both LAB and non-LAB species, while probiotic assessment primarily focuses on LAB strains, to present a scalable probiotic-postbiotic platform for enhancing food safety, functional food development and potential for mitigating mycotoxin risks.