Avian pathogenic Escherichia coli (APEC) poses a global threat to poultry health and public safety due to its high lethality, limited treatment options, and potential for zoonotic transmission via the food chain. However, long-term genomic surveillance remains limited, especially in countries like China where poultry farming is highly intensive. This study aimed to characterize the population structure, virulence traits, and antimicrobial resistance of 81 APEC isolates from diseased chickens collected over 16 years from Shandong and neighboring provinces in eastern China. The isolates were grouped into seven Clermont phylogroups, with A and B1 being dominant. MLST revealed 27 STs, and serotyping identified 29 O and 16 H antigens, showing high genetic diversity. The minor phylogroups (B2, C, D, E, G) encoded more virulence genes and had higher virulence-plasmid ColV carriage, with enrichment for iron-uptake, protectins, and extraintestinal toxins. In contrast, the dominant phylogroups A and B1 primarily carried adhesin and enterotoxin genes. Antimicrobial resistance was widespread: 76.5% of isolates were multidrug-resistant. The minor phylogroups exhibited higher tetracycline resistance (mediated by tet(A)), whereas the major phylogroups showed increased resistance to third- and fourth-generation cephalosporins (due to bla_CTX-M-type ESBL genes). These findings offer crucial data for APEC prevention and control, safeguarding the poultry industry and public health.

This study aimed to optimize the extraction process of Honeysuckle leaf polysaccharides (HLP) and investigate their regulatory effects on immune function, as well as the underlying molecular mechanisms, in Cherry valley meat ducks. Using dried Honeysuckle leaves as the raw material, the water extraction-alcohol precipitation method was adopted to isolate HLP. Through single-factor experiments combined with response surface methodology (RSM), the optimal extraction parameters were identified as a solid-to-liquid ratio of 1:20, an extraction temperature of 90 °C, and an extraction time of 80 min, with a corresponding polysaccharide yield of 5.46 ± 0.18 %. A 21-day gavage administration model was established in 3-day-old Cherry valley ducklings. Combined in vivo and in vitro assays demonstrated that HLP exerted no cytotoxicity at concentrations ranging from 5 to 3000 μg/mL. HLP significantly increased immune organ indices in ducklings and markedly enhanced peripheral blood lymphocyte viability. Furthermore, co-administration of HLP with lipopolysaccharide (LPS) synergistically promoted lymphocyte proliferation. Transcriptomic profiling analysis revealed that HLP exerts immunomodulatory effects primarily by regulating the peroxisome proliferator-activated receptor (PPAR) signaling pathway and the cytokine-cytokine receptor interaction pathway. This study optimized the HLP extraction process and elucidated its multi-pathway synergistic immunomodulatory mechanism in poultry, thereby providing robust experimental and theoretical support for the development of HLP as a natural immunomodulator in sustainable livestock and poultry health management.