Serotyping and Identification of Antimicrobial Resistance Genes in Avian Pathogenic <i>Escherichia coli</i> Isolated from Poultry Flocks in Jiangxi Province, China

Avian pathogenic <i>Escherichia coli</i> (APEC) is an important bacterial pathogen that causes severe respiratory and systemic infections in poultry. Our previous research investigated the prevalence and antimicrobial resistance phenotypes of APEC isolated from poultry flocks in Jiangxi Province, China. The present study aims to further identify the serotypes and the carbapenem-resistant gene <i>bla</i>_NDM in APEC strains. Serotype investigations revealed that the most dominant serotype was O24 (53.2%), followed by O78 (11.9%), O2 (3.2%), O18 (2.4%), O45 (0.8%), and O88 (0.8%). Serotypes O1, O30, and O65 were not detected, and 35 strains (27.8%) were un-typed. The identified genes <i>bla</i>_NDM-5 and <i>bla</i>_NDM-1 shared a close phylogenetic distance with <i>Klebsiella sp.</i> and <i>Acinetobacter sp</i>. isolated from river and human feces, respectively. Two APEC strains carrying <i>bla</i>_NDM-5 and <i>bla</i>_NDM-1 were subjected to whole-genome sequencing and analysis. The results showed that <i>bla</i>_NDM-5 was associated with the mobile genetic element IS5 and <i>bla</i>_NDM-1 was associated with the mobile genetic element ISAba125. Current study findings can be helpful for effective vaccine development and provide a deep understanding of APEC infections and antimicrobial resistance in poultry flocks.