Future-ready antimicrobials: harnessing organic acids to override Ca2+-driven barrier failure during Salmonella infection.

Organic acid mixtures are widely employed as feed additives to suppress enteric pathogens, yet their mechanisms of host protection at the intestinal epithelium remain unclear. Salmonella Typhimurium is a major cause of foodborne illness and mainly affects the caecal epithelium in poultry, where disruption of epithelial junctions enables bacterial adhesion, invasion and systemic spread. In this study, we examined the effects of a sub-inhibitory concentration of a commercial organic acid mixture, AuraShield (As) 0.25%, on S. Typhimurium SE10/72 infection in primary chicken caecal epithelial cells (PECC). Infected PECC showed decreased E-cadherin levels, altered zonula occludens-1 (ZO-1) and occludin mRNA expression and higher intracellular Ca²+, indicating junctional disruption and increased vulnerability to invasion. Treatment with 0.25% As significantly reduced bacterial adhesion and invasion, restored E-cadherin mRNA and protein expression along with its membrane localization and shifted ZO-1 and occludin transcript levels towards those of uninfected controls. Simultaneously, intracellular Ca²+ levels decreased towards baseline. These findings indicate that As protects the intestinal epithelium by maintaining E-cadherin-mediated adherens junctions, supporting tight junction gene expression and modulating Ca²+-dependent signalling during Salmonella infection. This research advocates the use of organic acid mixtures as host-directed interventions to strengthen the gut barrier and restrict pathogen colonization in poultry.