Whole genome sequencing analysis of avian pathogenic Escherichia coli from China

•A total of 35 different O types, 22 H types, and 29 ST types were found in APEC isolates, with great genetic diversity.•Several virulence-related genes (VAGs) were detected with high frequency in APEC isolates.•Several VAG clusters were significantly associated with phylogroup B2, D, and F but very rarely from phylogroups C and E.•Identified several VAGs that have been reported in other E.coli pathotypes but not in APEC. Avian pathogenic Escherichia coli (APEC) can cause localized or systemic infection in poultry herds, i.e., colibacillosis, which is an economically devastating bacterial disease of the poultry industry worldwide. Additionally, some APEC may have zoonotic potential. In this study, we sequenced 125 APEC isolates from chickens and ducks with obvious clinical symptoms in poultry farms in China and performed genomic epidemiological analysis along with 16 APEC reference genomes downloaded from NCBI. The phylogenetic analysis indicated a great diversity of APEC isolates, and a total of 35 different O types, 22 H types, and 29 ST types were identified. Several virulence-associated genes (VAGs), such as ompT (96.45 %), iss (97.87 %), and hlyF (90.78 %), as well as four complete siderophore gene clusters, including the Sit transport system (86.52 %), aerobactin (89.36 %), salmochelin (79.43 %), and yersiniabactin (54.61 %), were detected in APEC isolates with high prevalence, which could serve as virulence markers of APEC. Several virulence-associated gene clusters, including the two T6SS systems and the K1 capsule biosynthesis gene clusters, were significantly associated with APEC of phylogroups B2, D, and F but very rarely encoded by the APEC from phylogroups C and E. In addition, several virulence-associated genes, which have been reported in other E. coli pathotypes but have not been reported in APEC, were identified in this study. Our findings in this study have implications for a better understanding of APEC evolution and pathogenesis and may lead to the development of new diagnostic tools for APEC.