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Abstract
It is apparent that avian pathogenic Escherichia coli (APEC) causes multi-factorial diseases, which involves host-pathogens interactions, APEC strains cause a great diversity of diseases in birds and are responsible for great economic losses in the avian industry (Gerson et al., 2009).
The present study includes:
1-Isolation and identification E. coli from affected broiler chickens.
2-Detection of virulence factors of pathogenic E. coli phenotypically by congo red binding capacity or haemolysis on blood agar medium and genotypically by detection of virulence associated genes like astA, STa and VT2 genes.
In the present study a total of 150 collected internal organs from broiler birds showing signs of septicemia and respiratory disease. The samples were examined bacteriologically and the isolates were confirmed biochemicaly.
The obtained results were summarized as following:
54% of collected internal organs from affected broiler birds were found harboured E.coli.In case of septicemic birds E. coli was isolated from spleen with highest incidence (60%) then liver (50%) and lowest incidence from heart blood (40%), in case of birds showing respiratory symptoms the highest incidence was from air sac (33.3%) then spleen (18.1%) but heart blood (15%), had higher incidence than liver (10.8%).
The association between E. coli strain and bird age revealed that E. coli infection increase with aging as the high incidence was at 30-50 days (24.24%), then 20-30 days (12.12%) and lowest incidence at 1-20 days (11.76%).
from a total of 27 identified E. coli isolates cultivated on blood agar, 2 isolates (7.4%) showed α-haemolysis.
The congo red binding capacity revealed that all isolates could bind congo red and give positive results (red colonies).
Using PCR for detection of ast A gene for 12 E.coli isolates revealed that 4 isolates (33.33%) were positive.
Using PCR for detection of STa gene for 12 E.coli isolates revealed that ony one isolate (8.33%) was positive.
In correlation between astA and STa production indicated that one isolate was positive for both.
In correlation between haemolytic activity and STa production indicated that one isolate was α-haemolytic producing organism and enterotoxigenic.
Using PCR for detection of VT2 gene for 12 E.coli isolates revealed that none isolate was VTEC.
E. coli strains isolated from visceral organs of chickens with colisepticemia and respiratory affections do not commonly produce verotoxin (VT2) and only one isolate produce enterotoxin (STa).