Antimicrobial resistance and genomic characteristics of avian Pasteurella multocida

Pasteurella multocida, the cause of fowl cholera, poses a significant economic threat to poultry. The escalation of antimicrobial resistance (AMR) in this pathogen, driven by drug misuse, is a serious concern. Crucially, a comprehensive understanding of AMR patterns, molecular epidemiology, and virulence in Chinese avian strains is still lacking. This study aimed to elucidate the phenotypic and genomic characteristics of P. multocida strains isolated from avian in Zhejiang Province, China.

Twenty avian-origin P. multocida strains isolated in Zhejiang Province were subjected to antimicrobial susceptibility testing, whole-genome sequencing, and virulence assessment. Resistance was most frequent to florfenicol (65%) and tetracycline (50%). Multi-Locus Sequence Typing analysis revealed that ST471 and its closely related variant ST129 collectively constituted the dominant clonal group. A total of 13 resistance genes belonging to 5 major classes were identified, with floR (75%), sul2 (50%), and tet (B) (50%) exhibiting the highest prevalence. In the Galleria mellonella model challenged with 1.5 × 10⁷ CFU/larva, ST471 strains exhibited a slower killing rate compared to ST129 strains, while the ST7 strain demonstrated low virulence.

This study demonstrates the increasing prevalence of avian P. multocida in China, specifically the sustained circulation of ST129 and the recent emergence of ST471, particularly in ducks. These findings underscore the urgency of continuous monitoring of strain dissemination and the evolution of multidrug resistance, providing a scientific basis for precise and rational antimicrobials use in farms and for blocking the spread of potentially high-risk strains.