To examine the genetic background of avian pathogenic
Escherichia coli
(APEC) that affects virulence of this microorganism, we characterized the virulence genes of 101 APEC strains isolated from infected chickens between 1985~2005. Serotypes were determined with available anti-sera and median lethal doses were determined in subcutaneously inoculated chicks. The virulence genes we tested included ones encoding type 1 fimbriae (
fimC
), iron uptake-related (
iroN
,
irp2
,
iucD
, and
fyuA
), toxins (
lt
,
st
,
stx1
,
stx2
, and
vat
), and other factors (
tsh
,
hlyF
,
ompT
, and
iss
). Twenty-eight strains were found to be O1 (2.0%), O18 (3.0%), O20 (1.0%), O78 (19.8%), and O115 (2.0%) serotypes. The
iroN
(100%) gene was observed most frequently followed by
ompT
(94.1%),
fimC
(90.1%),
hlyF
(87.1%),
iss
(78.2%),
iucD
(73.3%),
tsh
(61.4%),
fyuA
(44.6%), and
irp2
(43.6%). The strains were negative for all toxin genes except for
vat
(10.9%). All the strains were classified into 27 molecular pathotypes (MPs). The MP25, MP19, and MP10 pathotypes possessing
iroN-fimC-ompT-hlyF-iucD-tsh-iss-irp2-fyuA
(22.8%),
iroN-fimC-ompT-hlyF-iucD-tsh-iss
(21.8%), and
iroN-fimC-ompT-hlyF-iss
(11.9%) genotypes, respectively, were predominant. Redundancy of iron uptake-related genes was clearly observed and some strains were associated with higher mortality than others. Therefore, strains with the predominant genotypes can be used for diagnosis and vaccine.
