Epidemiological Prevalence of Avian Pathogenic Escherichia coli Differentiated by Multiplex PCR from Commercial Chickens and Hatchery in Korea

We examined 216 Escherichia coli (E. coli) isolated from chickens and environmental specimens from hatcheries between 2005 and 2006 in order to evaluate the epidemiological prevalence of avian pathogenic E. coli (APEC) in Korea tentatively by multiplex PCR. The multiplex PCR which was used as tentative criteria of APEC targets 8 virulence-associated genes; enteroaggregative toxin (astA), increased serum survival protein (iss), iron-repressible protein (irp2), P fimbriae (papC), aerobactin (iucD), temperature-sensitive hemagglutinin (tsh), vacuolating autotransporter toxin (vat), and colicin V plasmid operon (cva/cvi) genes. The number of detected genes could be used as a reliable index of their virulence. It was demonstrated that E. coli strains already typed as APEC always harbor 5 to 8 genes, but non-APEC strains harbor less than 4 genes. Assuming the criteria of APEC is a possession of more than 5 virulenceassociated genes, we discriminated 24 APEC strains among the 216 E. coli strains. Contamination rates of APEC in the field were 31.3% in layers, 14.0% in broilers, 2.7% in broiler breeders, and 0.0% in environmental specimens from hatcheries. The combinational tendency of APEC examined is a fundamental possession of astA, iss and iucD genes and addition of cva/cvi, tsh, vat, and irp2 genes which have a critical importance for virulent traits of APEC. Compared with intravenous chicken challenge or embryo lethality assay, multiplex PCR method could be useful to discriminate APEC rapidly for convenient diagnosis.