Identification and functional characterization of novel probiotic lactic acid bacteria with potent antifungal activity against Alternaria species

Alternaria species are among the most destructive phytopathogenic fungi affecting tomato production, with notable implications for crop yield and food safety. In this study, fourteen lactic acid bacteria (LAB) isolates from traditional Iranian fermented dairy products were screened for their probiotic and biocontrol potential. Two strains, Lactiplantibacillus pentosus ABRIIFBI50 and L. plantarum ABRIIFBI51, showed the highest antifungal activity against Alternaria solani and A. alternata (mycelial growth inhibition > 70%) and were selected for further characterization. Both isolates exhibited strong antifungal activity in dual culture and cell-free supernatant assays, suggesting the involvement of extracellular metabolites. They also demonstrated pronounced antibacterial activity, with larger inhibition zones against Gram-positive pathogens (29.6–35.2 mm) than Gram-negative bacteria (19.5–24.5 mm). In addition, both strains displayed high survival under simulated gastrointestinal conditions (> 79%), strong adhesion to Caco-2 cells (> 71%), non-hemolytic behavior, and susceptibility to all tested antibiotics. These findings indicate that the selected isolates possess multifunctional in vitro properties that are relevant to both probiotic and biological control applications. However, these results are based solely on in vitro assays, and further greenhouse, field, and in vivo studies are required to validate their practical applicability.