Abstract:

Among the 282 E.coli strains isolated from ducklings typically showing E.coli septicemia in large-scale duck farms in Southwest China, the serotypes of 210 strains were identified. The results showed that totally 37 serotypes were obtained, of which serotypes of O93, O78, O92 and O76 accounted for 43.8% and were the prevalent serotypes, and serotypes of O46, O32&O93, O60&O93 were isolated from ducks at the first time.The pesticin receptor gene (fyuA) within the highly pathogenecity islands (HPI), iron regulatory protein gene (irp), type 1 pilus essential protein gene (fimC), the pap pilus structural protein gene (papA) and serum tolerance associated gene (iss) of the 210 pathogenic E.coli strains isolated from ducks showing clinical signs and the 28 E.coli strains isolated from cloacal swab of clinically healthy ducklings were detected by the method of polymerase chain reaction (PCR) and nucleic acid sequence analysis.The results demonstrated that the genes of fyuA, irp2, fimC, papA and iss were detected from pathogenic E.coli strains isolated from ducks showing clinical signs and account for 41.0%, 43.3%, 92.9%, 97.6% and 96.7% respectively, and the corresponding genes detected from E.coli strains isolated from clinically healthy ducklings account for 21.4%, 25.0%, 92.9%, 100% and 92.9% respectively. The results showed that there were no significant difference (P＞0.05) of iss, fimC and papA gene between the E.coli strains isolated from ducklings showing clinical signs and that isolated from clinically healthy ducklings. With the respects of papA gene detection, there were significant difference (P<0.05) between the E.coli strains isolated from ducks showing clinical signs and that isolated from other hosts of chickens, swine and humans. The fyuA gene was widely distributed in ducklings and its detection rate in ducklings showing clinical signs was significantly higher (P<0.05) than that in clinically healthy duckling. There was a close positive correlation between the fyuA gene and the pathogenicity of E.coli. Furthermore, the fyuA gene was closely related with the specific serotype of O78. The detection rate of fyuA, irp2, fimC, iss and papA in ducklings showing clinical signs (37.6%, 79/210) was significantly higher (P＜0.01) than that in clinically healthy ducklings（14.3%, 4/28）.

Key words: ducklings, pathogenic E.coli, serotype, virulence associated gene, molecular epidemiology