Twenty-Three Years of Surveillance in Chinese Avian Pasteurella multocida Reveals Declining Antimicrobial Resistance but Increasing Therapeutic Challenges.
Pasteurella multocida (Pm) is an important veterinary and zoonotic pathogen that causes significant economic losses in poultry production. However, long-term surveillance studies integrating antimicrobial resistance (AMR), biocide tolerance, and genomic epidemiology of Pm remain scarce. In this study, we investigated the antimicrobial susceptibility, biocide tolerance, and the phenotypic associations of 136 avian Pm isolates collected from six provinces in China between 2002 and 2024. Whole-genome sequencing was performed to characterize population structure, identify antimicrobial resistance genes (ARGs), and assess genotype-phenotype concordance. The A:L1:ST129 lineage remained the predominant clone throughout the 23-year surveillance period, with a high prevalence of AMR-associated traits observed within this lineage. Although resistance to several commonly used antimicrobial classes declined significantly after 2021, florfenicol resistance continued to increase, suggesting an emerging challenge for the clinical management of pasteurellosis. While the isolates generally exhibited low tolerance to the four representative biocides tested, phenotypic correlations were observed between AMR profiles and biocide tolerance patterns. Furthermore, substantial phenotype-genotype discordance was observed, indicating that the presence of ARGs alone may not be sufficient to accurately predict antimicrobial susceptibility. Overall, this study provides a longitudinal assessment of long-term AMR trends, biocide tolerance, and genomic epidemiology of avian Pm in China, offering epidemiological evidence for monitoring AMR trends and improving antimicrobial management strategies in poultry production.