Molecular epidemiology, antimicrobial resistance, virulence profiling, and pathogenicity of bovine Pasteurella multocida isolates from Hebei Province, China: Dominance of the A:L3-ST79 clonal lineage.

Abstract

Background and aim: Pasteurella multocida is an important bacterial pathogen associated with bovine respiratory disease and septicemia, causing substantial economic losses to the cattle industry worldwide. Increasing antimicrobial resistance has complicated disease management, yet comprehensive information on the molecular epidemiology, virulence characteristics, antimicrobial resistance, and pathogenicity of bovine P. multocida in Hebei Province, China, remains limited. This study aimed to characterize the circulating molecular lineages, virulence profiles, antimicrobial resistance patterns, and pathogenicity of bovine P. multocida isolates to support evidence-based surveillance, disease control, and rational antimicrobial use.

Materials and methods: Between 2023 and 2025, 162 clinical samples were collected from diseased cattle in seven prefecture-level cities of Hebei Province. P. multocida isolates were identified using conventional bacteriology and kmt gene polymerase chain reaction (PCR). Capsular and lipopolysaccharide (LPS) typing, RIRDC multilocus sequence typing, PCR detection of 15 virulence genes and 12 antimicrobial resistance genes, antimicrobial susceptibility testing against 14 antimicrobial agents using the Kirby-Bauer disk diffusion method, and pathogenicity evaluation in Kunming mice by determining the median lethal dose were performed.

Results: Sixty-four P. multocida isolates were recovered, yielding an overall isolation rate of 39.5%. Capsular type A (95.3%) and LPS genotype L3 (87.5%) predominated, with the A:L3 genotype accounting for 84.4% of all isolates. Sequence type ST79 represented 79.7% of all isolates and 94.4% of A:L3 isolates, demonstrating the dominance of the A:L3-ST79 clonal lineage. Twelve virulence-associated genes, including pfhA , tbpA , pmHAS , tadD , ompA, oma87, fimA, nanH, exbB, exbD, tonB, and hgbA, were detected in 96.9%-100% of isolates, whereas toxA was absent. The macrolide resistance gene mphE (92.2%) and sulfonamide resistance gene sul2 (87.5%) were the predominant resistance determinants. Multidrug resistance was identified in 95.3% of isolates, although high susceptibility was retained to doxycycline, enrofloxacin, ciprofloxacin, ceftiofur, and florfenicol. Representative A:L3-ST79 isolates exhibited high pathogenicity in mice, with median lethal dose values ranging from 8.06 × 10¹ to 6.44 × 10³ colony-forming units.

Conclusion: Bovine P. multocida isolates circulating in Hebei Province are dominated by a highly virulent and multidrug-resistant A:L3-ST79 clonal lineage with distinct molecular epidemiological characteristics. These findings provide a comprehensive baseline for molecular surveillance, vaccine development, antimicrobial stewardship, and targeted prevention and control strategies against bovine pasteurellosis in northern China.