Background and Objective: Acinetobacter baumannii is considered as an important agent in nosocomial infections. The problem facing the tratment of these bacteria is increasing resistance to antimicrobial agents such as carbapenems. The main mechanism of resistance to carbapenems in these bacteria is the presence of  oxacillinases genes, which belong to class D betalactamases. The aim of this study was   molecular diagnosis of Acinetobacter baumannii and  antimicrobial resistance pattern of these bacteria to antibiotics including imipenem and meropenem. 

Materials and Methods: Genus and species of clinical isolates of Acinetobacter were identified via biochemical tests and PCR method respectively. Their susceptibily  to imipenem and meropenem  were determined by disk diffusion method.  In order to identify carbapenem resistant genes (oxacillinases), multiplex PCR was used.

Results: 76 of 72 (94.7%) Acinetobacter species, possessed bla _oxa-51-like gene and were identified as  A.baumannii. Sixty one (84.7%) of isolates were resistant to imipenem and 70(97.2% ) were resistant to meropenem. Out of 76 isolates, 63 (87.5%) had an acquired bla _oxa-23like carbapenemase, 7 (9.7%%) possessed bla _oxa-24-like carbapenemase. None of the isolats contained either bla _oxa-58 or bla _oxa-143 carbapenemase.

Conclusions: It appears that cabapenem overutilization causes a selective pressure resulting in the emergence of antibiotic- resistant isolates. This study indicated that, the presence of bla _oxa-23 genes was significantly associated with the occurrence of resistance to carbapenems. So, investigation of antibiotic resistance genes in A. baumannii is necessary to control further dissemination of these resistance genes.