Characterization and Genomic Analysis of Pasteurella multocida NQ01 Isolated from Yak in China

Hemorrhagic septicemia (HS) is a fulminant bovine disease across Asia and Africa, yet Pasteurella multocida (P. multocida) isolated from yak is poorly reported. We isolated strain NQ01 from a fatal HS case in Xizang, China and identified it as P. multocida B: 2 by morphology, Gram stain, and PCR (kmt1+, bcbD+, LPS L2). NQO1 formed smooth, non-hemolytic colonies. After Gram staining, the cells appeared as red rods with bipolar staining. Antimicrobial testing showed broad susceptibility to β-lactams, aminoglycosides, tetracyclines, fluoroquinolones, midecamycin, florfenicol, polymyxin, and vancomycin, with resistance to metronidazole, trimethoprim sulfamethoxazole, and clindamycin. Streptomycin and ofloxacin had intermediate activity. In mice, the intraperitoneal and intranasal LD50 values were 40. 64 CFU/mL and 9. 53 × 106 CFU/mL, respectively. The intranasal fatal cases were characterized by bacteremia with multifocal disseminated intravascular coagulation involving lung, liver, and spleen. The complete genome comprises a single 2. 33 Mb chromosome (40. 47% GC, 2115 CDS, no plasmids) with only one resistance gene (EcoEFTuPLV) and 28 virulence genes spanning adhesion (tadA, rcpA, ppdD, pilB, tuf/tufA, htpB, PMRS00430, PMRS00425, PMRS08640), immune modulation (lpxB/C/D, msbB, manB, rfaE/F, gmhA/lpcA, kdsA, pgi, wecA, galE, bexD’, ABZJRS06285, ABD1RS00310), and nutritional/metabolic factor (hgbA, hemR, hemN), plus a YadA-like factor. Phylogenetically, NQ01 clusters with regional B: 2 bovine/yak isolates. Collectively, these data define NQ01 as a highly virulent, low-resistance yak isolate and a practical model for natural-route HS pathogenesis and targeted control in high-altitude pastoral settings yaks.