Escherichia coli is a commensal bacterium of the bird's intestinal tract, but it can
invade different tissues resulting in systemic symptoms (colibacillosis). This disease
occurs only when the E. coli infecting strain presents virulence factors (encoded
by specific genes) that enable the adhesion and proliferation in the host organism.
Thus, it is important to differentiate pathogenic (APEC, avian pathogenic E. coli)
and non-pathogenic or fecal (AFEC, avian fecal E. coli) isolates. Previous studies
analyzed the occurrence of virulence factors in E. coli strains isolated from birds
with colibacillosis, demonstrating a high frequency of the bacterial genes cvaC, iroN,
iss, iutA, sitA, tsh, fyuA, irp-2, ompT and hlyF in pathogenic strains. The aim of
the present study was to evaluate the occurrence and frequency of these virulence
genes in E. coli isolated from poultry flocks in Brazil. A total of 138 isolates of
E. coli was obtained from samples of different tissues and/or organs (spleen, liver,
kidney, trachea, lungs, skin, ovary, oviduct, intestine, cloaca) and environmental
swabs collected from chicken and turkey flocks suspected to have colibacillosis in
farms from the main Brazilian producing regions. Total DNA was extracted and the 10
virulence genes were detected by traditional and/or real-time PCR. At least 11 samples
of each gene were sequenced and compared to reference strains. All 10 virulence factors
were detected in Brazilian E. coli isolates, with frequencies ranging from 39.9% (irp-2)
to 68.8% (hlyF and sitA). Moreover, a high nucleotide similarity (over 99%) was observed
between gene sequences of Brazilian isolates and reference strains. Seventy-nine isolates
were defined as pathogenic (APEC) and 59 as fecal (AFEC) based on previously described
criteria. In conclusion, the main virulence genes of the reference E. coli strains
are also present in isolates associated with colibacillosis in Brazil. The analysis
of this set of virulence factors can be used to differentiate between APEC and AFEC
isolates in Brazil.