Abstract
A total of 54 broiler flocks during the first two weeks of life was used to investigate the incidence of avian pathogenic
E. coli
in Egypt; 28 isolates (51.85%) were revealed by colony morphology and biochemical identification which then investigated for their serogroups and only 18/28 isolates were serotyped. The most prevalent serotypes were O115, O142, O158, O55, O125, O114, O27, O20, and O15. By application of polymerase chain reaction (PCR), 83.3% (15/18) of the serotyped isolates were confirmed to be
E. coli
, and 93.3% (14/15), 46.6% (7/15), and 20% (3/15) of isolates harbored the
iss
,
iutA
, and
fimH
genes, respectively. Virulence testing of the selected 13
APEC
isolates on the specific-pathogen-free (SPF) chicks revealed them to be highly virulent (15.4%), moderately virulent (23.1%), and avirulent (61.5%); however, all isolates (100%) were extremely virulent towards SPF embryonated chicken eggs. Antibiotic resistance (100% of isolates (n = 13)) was observed for ampicillin, amoxycillin–clavulanic acid, and tetracyclines, colistin (92.31%; 12/13), doxycycline and spiramycin (84.62%; 11/13), florfenicol (69.23%; 9/13), cefotaxime (61.54%; 8/13), and ciprofloxacin (53.85%; 7/13). The highest percentage of sensitivity (53.85% of isolates; 7/13) was recorded for ofloxacin and enrofloxacin followed by gentamycin (46.15%; 6/13). The results suggest that the diagnosis of
APEC
with PCR is rapid and more accurate than traditional methods for
E. coli
identification; moreover, the presence or absence of
iss, iutA,
and/or
fimH
genes is not an indicator of in vivo pathogenicity of
APEC
. Thus, further studies, including a wider range of virulence genes and gene sequencing, are required. In addition, serotyping has no effect on the virulence of
APEC
.