Lactiplantibacillus plantarum-fermented shallot (Allium cepa L.) bulb in drinking water as a potential antibiotic alternative against Salmonella pullorum infection in broilers.

Salmonella pullorum infection causes severe economic losses in the poultry industry, while the rising threat of antimicrobial resistance necessitates sustainable alternatives to antibiotics. This study evaluated the protective efficacy of Lactiplantibacillus plantarum 1582-fermented shallot (Allium cepa L.) extract (FS) administered via drinking water in broilers challenged with S. pullorum NCTC10705. A total of 300 one-day-old male chickens were randomly allocated to six groups: negative control (NC), positive control (PC), antibiotic (AB), and three FS inclusion levels (1%, 2%, and 3%). While S. pullorum significantly impaired growth performance in the PC group (p < 0.05), FS supplementation, particularly at 2-3%, restored body weight gain and survival rates (90.0-91.8%) to levels comparable to the NC and AB groups. Mechanistically, FS modulated immune responses by restoring serum IgA and IgM levels, downregulating pro-inflammatory cytokines (TNF-α, IFN-γ), and upregulating IL-4. Furthermore, FS enhanced intestinal barrier integrity by increasing villus height and upregulating tight junction protein ZO-1 (with Claudin-2 restored to control levels). Microbiological analysis revealed that FS significantly reduced cecal Salmonella and E. coli loads while promoting beneficial Lactiplantibacillus spp. (p < 0.05). These findings demonstrate that water-based supplementation of fermented shallot extract effectively mitigates S. pullorum infection by reinforcing gut health and immunity, positioning it as a promising antibiotic alternative in poultry production.