Mehdi Shirdoust - Pediatric Infections Research Center, Research Institute for Children Health, ShahidBeheshti University of Medical Sciences, Tehran, Iran
Fatemeh Fallah - Pediatric Infections Research Center, Research Institute for Children Health, ShahidBeheshti University of Medical Sciences, Tehran, Iran
Shahnaz Armin - Pediatric Infections Research Center, Research Institute for Children Health, ShahidBeheshti University of Medical Sciences, Tehran, Iran
Ghazaleh Ghandchi - Pediatric Infections Research Center, Research Institute for Children Health, ShahidBeheshti University of Medical Sciences, Tehran, Iran

Background and Objectives: The appearance and spread of carbapenem-resistant Acinetobacter baumannii (CRAB) pose an important challenge for optimization of antibiotic therapies and outbreak preventions.Ability to produce OXA-type carbapenemases is the most prevalent mechanism for resistance to carbapenem in this opportunistic pathogen. We aimed to evaluate the prevalence of OXA-type carbapenemases among clinical isolates of A. baumanniiin oneof the referral hospitals in Tehran. Materials and methods: In this cross sectional study,90 A.baumanniiwere collected fromdifferent clinical specimens in Milad hospital, Tehran. Collected strains were identified by conventional biochemistry and microbiological methods such as;TSI, oxidase and growth on 42 o C. Antibiotic susceptibility testing was done according to CLSI guide- lines. DNA extraction was prepared for Multidrug- Resistant strains by special DNA extraction kit. Oxa- 23, Oxa-48, Oxa- 58, Oxa- 40 and Oxa- 24 genes as most common Oxa type genesin A. baumannii were detected by PCR. The sequencing was used to confirm PCR results. Results: 90 collected A. baumannii were confirmed according to phenotypic methods. Colistin remains the most effective antibiotic in MDRA. baumannii and all of strains were susceptible to it. Most of resistance was observed against cefotaxim, ceftazidim and imipenem. 69, 28, 24 and 53 Oxa- 23, Oxa-48, Oxa- 40 and Oxa- 24 were identified by PCR and sequencing, respectively. Conclusion: The results of this study indicate that the presence of high rate of Oxa- 23 and Oxa- 24 in MDR A.baumannii and they are the most prevalent of OXA type enzyme in etiology of nosocomial infections in Iran. These genes are located on transferable genetic elements and can spread rapidly in hospitals. Thus, nosocomial infection committee of hospital should consider this high prevalence of plasmid resistance gene.