Characterization and Pathogenicity of Mannheimia glucosida Isolated from Sheep

Bacteria of the genus <i>Mannheimia</i> are major pathogens of respiratory diseases in ruminants and pose a significant threat to the global ruminant industry. However, the biological characteristics and pathogenic mechanisms of <i>Mannheimia glucosida</i> remain unclear. In this study, we isolated five strains of <i>M. glucosida</i>, which specifically hydrolyzed esculin, from sheep with respiratory disease in China. All five strains of <i>M. glucosida</i> were found to encode the adhesion-related gene <i>adh</i> and the anti-phagocytosis-related gene <i>plpD</i>, as determined by a virulence gene assay. Moreover, all <i>M. glucosida</i> isolates were resistant to streptomycin. Phylogenetic analysis based on <i>16S rRNA</i>, <i>infB</i>, and <i>sodA</i> genes showed that the <i>sodA</i> gene could be a valuable indication for the analysis of bacterial genetic evolution in the genus <i>Mannheimia</i>. By mouse modeling, <i>M. glucosida</i> D251 was further found to cause multiorgan damage with an LD₅₀ of 1.35 × 10⁶ CFU. Meanwhile, by combining whole genome sequencing with bioinformatic analysis, we found that the D251 genome encodes a large number of virulence and drug resistance genes. Finally, we established a highly sensitive and specific PCR assay for <i>M. glucosida</i>. Collectively, these results indicate that <i>M. glucosida</i> may be an important pathogen in respiratory disease in sheep in China and provides a theoretical basis for the clinical diagnosis and treatment of this disease.