Effects of phytobiotics on intestinal barrier function and gut microbiome in weaned piglets challenged with enterotoxigenic Escherichia coli

Weaned piglets are highly susceptible to infections caused by enterotoxigenic <i>Escherichia coli</i> (ETEC), and phytobiotic supplementation has been explored as a potential strategy to prevent or mitigate such infections during the weaning period. However, comprehensive studies on the specific effects of phytobiotics on pig gut health and microbiota composition remains limited. Therefore, this study aimed to investigate the effects of various phytogenic feed additives (PFAs) on intestinal barrier function and gut microbiota composition in weaned piglets challenged with ETEC. A total of 63 weaned piglets ([Yorkshire × Landrace] × Duroc), 28 days old with an initial body weight of 8.03 ± 0.43 kg, were used in a 21-day trial. Piglets were randomly assigned to one of seven treatment groups: NC, negative control (basal diets without <i>E. coli</i> challenge); PC, positive control (basal diets + <i>E. coli</i> challenge); T1, PC + 0.04 % P1; T2, PC + 0.01 % P2; T3, PC + 0.10 % P3; T4, PC + 0.04 % P4; T5, PC + 0.10 % P5. The five phytobiotic materials were as follows: a bitter citrus extract rich in flavonoids (P1), a microencapsulated blend of thymol and carvacrol (P2), a composite of P1 and P2 (P3), a grape polyphenol-based mixture containing green tea and hops (P4), and a fenugreek seed powder rich in saponins (P5). Piglets in challenged groups were orally inoculated with ETEC at a concentration of 1.2 × 10¹⁰ CFU/mL from days 8 to 10. The results showed that PFA supplementation upregulated the expression of tight junction and mucin-related genes including ZO-1 and MUC3. Based on 16S rRNA gene sequencing, distinct microbial shifts were observed depending on the specific PFA composition. The relative abundances of beneficial genera such as <i>Lactobacillus</i>, <i>Olsenella</i>, and <i>Collinsella</i> increased following PFA supplementation. These genera are known to be associated with short-chain fatty acid production, improved gut health, and increased resistance to pathogens. Additionally, increases in <i>Acinetobacter</i> and <i>Medioterraneibacter</i>, which may be involved in the metabolism of plant-derived compounds, were observed. Collectively, our results suggest that PFAs may enhance gut health and contribute to the stabilization of the intestinal microbiota in weaned piglets.