History and Objectives: Due to prevalence of urinary tract infections and due to the importance of therapy and misuse of antibiotics which leads to augmented antibiotics resistance and since E.coli is the causative agent in 80 to 90% of cases, the present study is undertaken in order to determine the resistance of antibiotics by 50 different E.coli species separated from urine samples from city of Isfahan in 1998.

Materials and Methods: A descriptive study on patients referred to clinical diagnostic laboratories and hospitals of Isfahan was carried out. After confirmation of infection, the infectious agents were transferred to the department of microbiology of Isfahan Medical University. Classic microbiological techniques were used to identify the cells. Their resistance to the 13 different antibiotics (From 0.25 µg/ml to 128 µg/ml concentrations) and their MIC’s were determined.

Results: From 50 different E.coli species 72%, 64%, 58%, 56%, 52%, 52%, 38%, 34%, 32%, 24%, 22%, 20% and 18% were resistant to ampicillin, carbinicyllin, tetracycline, chloramphenicol, cefoxitin, cephalothin, nitrofurantoin, ciprofloxacin, amikacin, gentamicin, co-trimoxazole, kanamycin, cefoxitin and nalidixic acid respectively. MIC for the above-mentioned cell were higher than the standard sensitive E.coli (E.coli ATCC 25922). All the isolated species were multiresistant.

Conclusion: In light of higher rate of E.coli resistance compared to other countries, due to availability of antibiotics as over the counter drugs, educational programs ought to be conducted and prescription of antibiotics should be restricted to the findings of laboratory findings.