Abstract
Necrotic enteritis (NE), caused by Clostridium perfringens, remains a major challenge in broiler chicken production. Probiotics represent a promising alternative strategy to mitigate NE by modulating intestinal immunity and microbiota composition. This study evaluated the effects of oral administration of the commensal bacterium Bacteroides thetaiotaomicron on immune responses, microbial profiles, and lesion development in broiler chickens challenged with C. perfringens. One-day-old male broilers (n = 120) were assigned to four groups and received either a low (1 × 10⁷ CFU) or high (5 × 10⁷ CFU) dose of B. thetaiotaomicron on days 1, 7, 14, and 21 post-hatch. Birds were subsequently challenged to induce NE. Ileal and cecal tonsil tissues were collected for gene expression analysis, and cecal contents were analyzed by 16S rRNA gene sequencing. High-dose B. thetaiotaomicron significantly reduced intestinal lesion scores compared with the positive control, whereas the low dose was ineffective. High-dose supplementation enhanced intestinal immune signaling, with increased expression of TLR2 and TLR4, primarily in the ileum. This was associated with increased expression of pro-inflammatory cytokines (IFN-γ and IL-1β) during the early post-challenge phase and sustained upregulation of regulatory cytokines (IL-10 and IL-2). The epithelial defense-associated cytokine IL-22 was upregulated in both the ileum and cecal tonsils, while TGF-β showed transient induction in the ileum. Markers of epithelial barrier integrity were improved, as evidenced by increased occludin expression, whereas ZO-1 expression remained unchanged. Microbiome profiling revealed that high-dose supplementation enriched beneficial taxa such as Lactobacillus while reducing the abundance of the pathogenic species Enterococcus cecorum. These findings highlight the potential of B. thetaiotaomicron as a probiotic strategy to enhance intestinal immunity and resilience against necrotic enteritis in broiler chickens.