Virulence and antibiotic resistance characteristics of Pasteurella multocida from sheep: integrated genomic and phenotype analysis.

Pasteurella multocida (Pm), a ubiquitous Gram-negative bacterium, causes respiratory diseases that pose a significant threat to the livestock industry. In this study, we performed whole genome sequencing, biological characteristics analysis, comparative genomics, antimicrobial susceptibility testing, and pathogenicity assessment to comprehensively characterize a clinical Pm isolate (designated YPm; GenBank accession number CM129929.1) from sheep. The genome of YPm comprises 2,304,730 base pairs with a GC content of 40.3% and encodes 2,140 protein-coding genes, including 126 virulence factors and 57 antimicrobial resistance genes. Genomic analysis identified the toxA gene within a genomic island and prophage region, suggesting its potential acquisition through horizontal gene transfer. The phenotypic characteristics of YPm were consistent with the genomic predictions, including high metabolic capacity and intermediate resistance to lincomycin. Concurrently, comparative genomics revealed the distinctive genomic structure and evolutionary distinctions of YPm. Antimicrobial susceptibility testing revealed intermediate resistance to lincomycin and clindamycin, while demonstrating sensitivity to all other tested antibiotics. Infection experiments in mice demonstrated significant bacterial colonization in the liver and lungs, accompanied by tissue damage and inflammatory reaction. This study characterizes the high virulence and multiple predicted antimicrobial resistance genes of an ovine-derived Pm capsular serotype D strain, providing molecular insights to inform clinical prevention and control.