Aim and back ground: In recent years the threat of acquisition of antibiotics resistance caused by over use of antibiotics is growing. The purpose of this study was to survey the pattern of antibiotic resistance and evaluate of Multi-drug resistance Escherichia coli and analyze the plasmid profile of these clinical strains.

Materials and Methods: This study was performed on 83 clinical Escherichia coli, obtained from four hospital (imam Khomeini, Alborz, Kasra, qaem) and two private laboratories (Razi and Kavosh), of Karaj city. Isolates were identified as Escherichia coli based on standard biochemical tests. The isolates were screened for Antimicrobial susceptibility test by 20 antibiotics using Kirby-Bauer disk diffusion method. Plasmid profiles of these isolates have been analyzed by alkaline lysis method.

Result: Antibiotic resistance pattern were observed as follows: Nitrofurantoin 8.4%, Tetracycline 63.8%, Amoxicillin 83%, Ofloxacin 30%, Levofloxacin 30%, Co-trimoxazole 59%, Amikacin 18%, Imipenem 25.3%, Choloramphenicol 16.9%, Cephalexin 61.4%, Gentamycin 28.2%, Norfloxacin 33.7%, Nalidixic acid 56.6%, Cephalothin 48.2%, Ciprofloxacin 32.5%, Ceftazidime 27.7%, Ceftriaxone 37.3%, Ceftizoxime 16.9%, Cefotaxime 38.5%, Amoxycillin/Clavulanic acid 68.7%. Of 83 isolates 92.77% (77) isolates were resistance to more than two unrelated drugs. Of 83 isolates, 65 isolates, (78.3%) showed the presence of plasmid.

Conclusion: The results of this study indicate a growing resistance pattern to the first line antibiotics, prescribed for urinary tract infection. High presence of plasmids in these strains, play an important role in multidrug resistance in these bacteria.