Impact of Limosilactobacillus reuteri cell-free culture supernatant on stress-resistant Salmonella Typhimurium in seawater: antioxidant, anti-infective, and anti-adhesion effects.

Salmonellosis linked to fish consumption is a significant public health concern. Salmonella often contaminates fish through polluted water or improper handling, with increasing antibiotic-resistant strains in aquaculture. This study evaluated the antimicrobial, antioxidant, and anti-biofilm activities of the cell-free culture supernatant (CFCS) of Limosilactobacillus reuteri against normal and stressed Salmonella Typhimurium in seawater microcosms over four years. The CFCS exhibited minimum inhibitory concentrations (MIC) ranging from 16.66% to 30% under acidic conditions, whereas stressed strains showed increased resistance, with MIC reaching up to 60% at neutral pH. Antioxidant activity reached 38% (DPPH assay), and CFCS significantly reduced biofilm formation and bacterial adhesion by up to 52% on the fish cell line (SAF-1). Additionally, L. reuteri CFCS modulated the expression of genes related to oxidative stress (cat, sod, gr) and immune response (il1b, il6, il8). These findings highlight the potential of L. reuteri CFCS as a natural antimicrobial and anti-virulence agent in marine aquaculture, helping to address antibiotic resistance issues.