Abstract
Specimence of E. coli cultures isolated from different humane sources of infections (Urinary tract, diarrhea and otitis media) after identification, using cultural characters, biochemical tests and serotyping. These cultures classified according to their resistance to the antibiotics (Ampicilline, chloramphenicol, tetracycline and streptomycine sulfate) to five groups of E. coli isolates show variations in their resistance to these antibiotics in order to characterize the purified plasmid DNA of isolated E. coli, a group of properties were examined and they show that most plasmid DNA in these isolates are capable to transfer itself among E. coli isolates through conjugation process. In addition plasmid DNA shows ability to amplify its copy number after prolonged treatment of cultures with chloramphenicol except for one that purified from strain isolated from otitis media.