Comparative Genomic Characterization of Riemerella anatipestifer Isolates from Chickens, Ducks, and Geese in China.

The increasing detection of Riemerella anatipestifer in chickens poses severe challenges to the poultry industry. However, the genomic differences among R. anatipestifer isolates from different poultry hosts remain poorly understood. Here, we investigated host-associated genomic differences among 158 R. anatipestifer strains isolated from different hosts in China, using pan-genome, phylogenetic, virulence factor, and antimicrobial resistance analyses. The core-genome phylogeny showed no apparent separation according to host, sampling period, or geographic origin. Conserved genes including groEL, tufA, and katB were detected in all strains, whereas tviB and ureG displayed host-associated distribution patterns. More than 40 putative antimicrobial resistance (AMR) genes were detected across 158 R. anatipestifer strains, indicating the presence of multiple putative AMR determinants. Among these, blaRAD-1, blaRASA-1, and dfrA36 exhibited host-associated distribution patterns. Pan-genome analysis further identified host-associated genomic differences in R. anatipestifer. These included genes contributing to cell-surface modification pathways mediated by pglH, and genes involved in toxin-antitoxin system-dependent stress regulation via parD1/parE1 and yefM-yoeB. Overall, our comparative genomic characterization of R. anatipestifer characterizes host-associated genomic differences and provides a basis for further investigation of their biological significance.