Abstract
This study was aimed to determine bacterial agents which causing omphalitis in chicks. To achieve this purpose the following points were studied: Isolation and biochemical identification of E.coli and Staphylococcus aureus from yolk sac samples were collected from diseased chicks and detection virulence markers in isolated E.coli and Staphylococcus aureus by using phenotypic and genotypic markers of virulence. Phenotypic assay as the Congo red binding capacity of the isolated E.coli and the haemolytic activity of the isolated E.coli on blood agar medium were used. Genotypic
assay as detection of Adhesin-encoding genes of E.coli by using multiplex PCR and detection of Staphylococcus aureus super antigen genes by using multiplex PCR. This study was carried-out on random samples (150 samples) of yolk sac that were collected from different private chick hatcheries from newly hatched chicks. The samples were collected, labeled and transported in ice box to the laboratory of Department of Microbiology, Faculty of Veterinary Medicine, Alexandria University bacteriological identification was carried-out for the bacterial isolates of these samples. It could be concluded that, the main bacterial agents causing omphalitis include Staphylococcus aureus, E. coli, Proteus vulgaris, Proteus mirabilis, klebsiella pneumonia and Enterobacterhafniae.

Key words: Aerobic Bacteria, Omphalitis, Chicks