Genotypic and Biochemical Divergence of Avibacterium paragallinarum Isolates in China

<i>Avibacterium paragallinarum</i> is the causative pathogen of infectious coryza. Isolates of <i>A. paragallinarum</i> obtained from China between 2008 and 2022 were characterized using 16S rRNA, <i>HMPt210</i>, multilocus sequence typing, and biochemical tests to assess their genetic and biochemical diversity. All field isolates belonged to the same phylogenetic cluster together based on their 16S rRNA sequences. The similarity of the 16S rRNA sequences between the Chinese field isolates and type strain NCTC11296 was 96.5%-97.0%, and that among the Chinese field isolates was 99.7%-100%. Twenty typeable field isolates were categorized into A-1, B-1, and C-4 clades according to their <i>HMPt210</i> sequences, but positioned in separate subclades alongside reference strains within each clade. Variable biochemical characteristics were observed between the type strain NCTC11296 and field isolates, with most Chinese field isolates utilizing <i>myo-</i>inositol, L-fucose, arabitol, raffinose, and <i>N</i>-acetyl neuraminic acid, unlike the type strain. The type strain NCTC11296 could produce acid from dextrin and maltose, unlike the 24 Chinese field isolates. Among the 36 isolates tested, one new <i>infB</i> allele and five new sequence types (STs) were identified; the most prevalent ST for Chinese field isolates was ST1 (<i>n</i> = 19; 79.2%). These results suggest that the Chinese field isolates of <i>A. paragallinarum</i> were genetically and biochemically different from the type strain.