Outbreak of Colibacillosis in Intensive Chicken Farms: Pathogenicity and Molecular Characterization

Avian pathogenic E. coli (APEC) are generally considered to be the reservoir for human extraintestinal pathogenic E. coli (ExPEC): they share similar genetic characteristics and pathogenicity with no or minimal host specificity. In this study, we successfully isolated and identified an E. coli strain as the culprit responsible for serious colibacillosis outbreaks in intensive chicken farms in China in 2016. We investigated its phylogenetic classification (A, B1, B2, C, D, E, and F) by PCR analysis; its virulence and host range using challenge experiments with different animals; and its virulence factors, drug resistance genes, sequence type (ST), and related biological information through high-throughput sequencing. This isolate was found to belong to ST95, group B2, and serotype O18. The E. coli strain shows strong virulence in chickens with a minimum lethal dose (MLD) of 3 × 103 CFU/chicken and a strong virulence in mice with an MLD of 3 × 102 CFU/mouse and in rabbits with an MLD of 3 × 103 CFU/rabbit. Whole-genome sequencing showed that it consists of six types of prevalent resistance genes, 33 antibiotic efflux genes, and nine recognized virulent factors. The detailed data are available from GenBank (SRR13005645) for further study.