Antimicrobial resistance patterns and genomic characterization of Avibacterium paragallinarum isolates collected in China from 2013 to 2021

BACKGROUND: Avibacterium paragallinarum is the causative agent of infectious coryza in chickens and contributes to significant economic losses in poultry production. Antimicrobial therapy is widely used for disease control; however, increasing antimicrobial resistance (AMR) may compromise treatment efficacy. Long-term surveillance data on AMR in Av. paragallinarum in China remain limited. RESULTS: A total of 117 Av. paragallinarum isolates were analyzed, including 113 clinical isolates collected from 13 provinces in China between 2013 and 2021 and 4 historical international reference strains. Antimicrobial susceptibility to 16 antibiotics was assessed using the Kirby-Bauer disk diffusion method. High resistance rates were observed for ampicillin, clindamycin, compound sulfamethoxazole, nalidixic acid, and tetracycline. In contrast, erythromycin, azithromycin, ceftiofur, and spectinomycin retained high levels of susceptibility. Compared with historical strains, contemporary isolates exhibited increased resistance to several antimicrobial classes. Whole-genome sequencing of 15 representative isolates identified multiple resistance genes, including determinants associated with aminoglycoside, β-lactam, sulfonamide, and tetracycline resistance. The tigecycline resistance gene tet(X6) was detected in one isolate. CONCLUSION: This study first detects gene tet(X6) in Av. paragallinarum isolates. Continuous surveillance of its multidrug resistance and rational antimicrobial use are vital to curb resistance spread in poultry systems.