Introduction & Objective: One of the mechanisms of antibiotic resistance in gram negative bac-teria, particularly Klebsiella pneumonia strains, is the production of Extended-Spectrum β lactamase enzymes (ESBLs). Encoding genes of ESBLs are usually located on the plasmid and they are able to transfer to other gram-negative bacteria. Thus, due to the importance of resistance pattern recognition and its sensitivity to the β- lactam antibiotics, the above men-tioned issue was examined in this study.

Materials & Methods: In this study different clinical samples of Boroujerd and Hamadan Hos-pitals during 6 months were collected and identified by biochemical tests and Enterosystem kit. To confirm the strains, the Ure D gene was used as the internal gene of Klebsiella pneumoniae by PCR method. Antibiotic resistance by Disk diffusion method was performed. Phenotypic confirmatory test was used to determine the presence of ESBLs. MIC antibiotics of Ceftazidime and imipenem by E test method were determined.

Results: The results showed that the highest rate of Klebsiella pneumoniae strains resistance was related to Cefexime antibiotics 46.7%, Ceftriaxone 43.3%, Azthrunam 43.3%, Cefo-taxime 41.7%, Cotrimaksazol 40.8% , Ceftazidim 36.7% and the least resistance was related to antibiotics Imipenem 0% Sprofluksasin 16.7%, Cefepime 25% and Gentamicin 26.7%. 56 strains( 46.7%) were identified as ESBL –positive strains. Using E-test strip for Ceftazidim antibiotic, 66 strains were resistant , 10 strains intermediate ,and 44 strains were sensitive to Ceftazidim and by E test method for Imipenem antibiotic ,120 strains were sensitive.

Conclusion: The high prevalence of antibiotic resistance and ESBLs production in the cities which were studied indicates the need for screening of ESBLs in clinical samples by labora-tory and prescribing appropriate antibiotics with ?-lactamase inhibitory power and antibiotics together with clavulanic by physicians.