抑制APEC鸡源屎肠球菌的分离、鉴定及益生特性研究OA

To screen antibiotic alternatives with probiotic potential against avian pathogenic Escherichia coli(APEC)infection,male Dawu Jinfeng layer chicks were artificially challenged with the APEC O78 strain to establish an infection model.Resistant and susceptible chicken groups were identified according to clinical phenotypes.Microbial diversity in fecal samples from different groups was analyzed by 16S rRNA sequencing.Isolated strains were identified,and their antibacterial activity,acid tolerance,and bile salt tolerance were evaluated.A strain with superior properties was selected for whole-genome sequencing analysis,and its safety was further assessed through both in vitro and in vivo experiments.The results showed that the APEC infection model was successfully established,and resistant and susceptible chicken groups were identified.16S rRNA sequencing analysis demonstrated that the relative abundance of Enterococcus in resistant chicks was significantly higher than that in susceptible chicks(P<0.001),and the genus remained stably coexisting after infection.Five Enterococcus faecium strains were isolated from feces of eight resistant chicks.Among them,strain CP5 exhibited the strongest antibacterial activity against APEC O78 and showed excellent stress resistance.The complete genome length of CP5 was 2 738 879 bp.Clusters of Orthologous Groups(COG)functional annotation revealed that CP5 was enriched in genes related to carbohydrate transport and metabolism,translation,ribosomal structure and biogenesis,and transcription.Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway analysis indicated that carbohydrate metabolism,transmembrane transport,and translation pathways were predominant.In vitro safety evaluation showed that 1%-15%concentrations of CP5 cell-free supernatant exhibited no cytotoxicity toward human colorectal adenocarcinoma cells(Caco-2),while 5%and 15%concentrations significantly upregulated the mRNA expression of occludin(P<0.05).In vivo safety evaluation demonstrated that continuous gavage administration of a medium dose of CP5(3.0×10⁹ CFU/mL)for 14 d significantly increased the spleen index(P<0.05)and thymus index(P<0.01)in chicks.Administration of CP5 had no effect on hepatic alanine aminotransferase(ALT)or aspartate aminotransferase(AST)levels,whereas a high dose of CP5(5.0×10⁹ CFU/mL)significantly enhanced total antioxidant capacity(T-AOC)in the liver(P<0.01).These results indicate that E.faecium CP5 possesses strong antibacterial activity,intestinal barrier-enhancing capacity,and immunomodulatory functions,while exhibiting high in vitro and in vivo safety,providing a candidate probiotic strain and theoretical basis for the prevention and control of APEC-associated diarrhea in chicks.