It has been documented in nowadays the increase of bacterial resistance to antibiotics. So the current research aims to investigate the mechanism of the bacterial resistance and to achieve this goal the following has been done:First: A total of 7 E. coli isolates from quails liver, chickens liver and humans urine were identified biochemically by lactose fermentation, indole, citrate, methyl red, voges proskaur, triple sugar iron and sugar fermentation tests.Second: These isolates were studied for antimicrobial susceptibility patterns by disk diffusion and microdilution method.Third: Chromosomal DNA and plasmid of 7 E. coli isolates included in this study were subject to PCR with primers specific to blaTEM, blaSHV and blaOXA genes.The results were as follows:Disk diffusion susceptibility pattern against 7 E. coli isolates:Antimicrobial susceptibility patterns of 7 E. coli isolates examined by disk diffusion test. out of 7 E. coli isolates, 4 isolates were resistant to enrofloxacin (57.1%), 6 isolates were resistant to cefotaxime (85.7%), 7 isolates were resistant to trimetThe MIC range of 7 antibiotics against 16 isolates:Cefotaxime (mic ≥ 8 µg/ml), amoxicillin (mic≥ 2 µg/ml), enrofloxacin (mic ≥ 2 µg/ml) and gentamicin (mic≥ 4 µg/ml).