Isolation, Identification, and Biological Characteristics of Mannheimia haemolytica from Goats.

With the rapid expansion of the meat goat farming industry in China and intensified interregional movement of goats, respiratory diseases have become increasingly prevalent across domestic goat farms-particularly under suboptimal husbandry conditions-posing a significant challenge to effective disease prevention and control. Mannheimia haemolytica, a primary bacterial pathogen implicated in caprine respiratory disease, exhibits marked geographic variation in key phenotypic and genotypic traits, including serotype distribution and antimicrobial resistance profiles. To address this critical animal health concern, Mannheimia haemolytica was isolated from clinical specimens collected from multiple commercial goat farms in Jingmen City, Hubei Province, and performed an integrated phenotypic and genomic characterization, including Gram staining, biochemical identification, molecular biological identification, virulence gene identification, genetic and evolutionary analysis, antimicrobial susceptibility testing, pathogenicity assays, whole-genome sequencing, and qPCR detection. Our analysis identified a Mannheimia haemolytica strain belonging to serotype A2. Whole-genome analysis confirmed the presence of six core virulence-associated genes: LKT-C, gs60, fbpA, SodA, gapA, and dnaA. The isolated strain displayed a defined antimicrobial resistance profile and induced significant dysregulation of pro-inflammatory cytokine expression in infected murine lung tissue, thereby revealing mechanistic insights into its pathogenicity. Collectively, this study delivers a rigorously characterized reference isolate of caprine-derived Mannheimia haemolytica serotype A2, advances knowledge of its genomic landscape, virulence repertoire, and host-pathogen interplay, and provides a foundational evidence base to inform targeted, science-driven interventions against respiratory disease in goat production.