Epidemiological investigation and drug resistance analysis of avian pathogenic Escherichia coli (APEC) of Wenchang chickens in Hainan, China

Avian pathogenic Escherichia coli (APEC) is one of the major causes of poultry morbidity worldwide, severely reducing egg production and embryo hatchability in laying hens. Hainan Wenchang chicken is an important poultry breed in Hainan, China, and production of these chickens has been affected by APEC for a long time. In this study, in order to investigate the causes of low hatchability and a large number of weak chicks during the breeding of Wenchang chickens, a total of 130 strains of APEC were isolated from 591 chicken embryo samples collected from five large-scale farms of Wenchang chicken in Hainan area. The APEC isolates from Hainan Wenchang chicken embryos were analysed in terms of serotypes, drug resistance, genomes and evolutionary relationships. O8 was the main prevalent serotype of APEC from embryos, and the isolates were highly resistant to antibiotics and were multi-drug resistant. Of the isolates, 19.2% were resistant to 14 antibiotics with a resistance rate of more than 73%. The number of resistance genes carried by APEC isolates from embryos was stabilized at 53. The results of pan-genomic analysis showed that the genomes of Hainan Wenchang chicken embryo APEC isolates are concentrated in two evolutionary clusters, and isolates of the same serotype had extremely close evolutionary relationships. This study is the first large-scale isolation and analysis of APEC isolated from Wenchang chicken embryos, which can provide a reference for the prevention and control of APEC and antibiotic use in Hainan Wenchang chickens.RESEARCH HIGHLIGHTSType O8 is the most prevalent serotype of APEC isolated from Wenchang chicken embryos (Hainan, China).The isolates were more than 90% resistant to erythromycin, amoxicillin, ampicillin, and tetracycline.19.2% of the isolates were multi-resistant to more than 14 antibiotics.APEC of the same serotype isolated from Hainan Wenchang embryos have close relationships in the evolutionary tree of the core genome.