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The antimicrobial resistance are a worldwide increasing problem. Colistin represent a major group of polymyxins class that mostly resistance by gram negative bacteria, so the detection of colistin resistance genes are very important fo`r optimal patients care. Colistin (polymyxin E) old antibiotic used to treat infections caused by multiple drug resistant (MDR) Acinetobacter baumannii isolates. The aim of this study is to detect the colistin resistance in A. baumannii isolates obtained from patients with various clinical specimens. Six hundred specimens were collected during the period from September 2020 to December 2020 from three hospitals in Babylon Province/ Iraq. The clinical specimens included burn, blood, wound and urine. Morphological and biochemical tests were used for isolation and identification of bacterial isolates. These isolates were obtained as a pure and predominant growth from clinical specimens. Antibiotic susceptibility tests were carried out using disk diffusion method (DDT) and MIC by agar dilution method for phenotypic detection of colistin resistant isolates. PCR technique was performed to detect Mobilized Colistin Resistance (MCR) genes. Twenty isolates of A. baumannii out of 600 specimens (3.33%) were detected. Moreover, 9 isolates out of 20 tested(45%) showed heteroresistance to colistin by DDT while Minimum inhibitory concentration by agar dilution method showed 3(15%) out of 20 A. baumannii isolates resistant to colistin and have MIC value, 128 µg/ml. Furthermore, Colistin resistance genes (mcr1, mcr 2, mcr3, mcr4, mcr5) were investigated by PCR as following: mcr4, mcr5 detected predominantly in 15( 75%),11(55%) out of 20 A. baumannii isolates respectivel, however mcr1gene was detecetd in 3 ( 15%). While mcr 2, mcr3 were not detected in this study. This study included that, there was emergence of colistin resistance in MDR A.baumannii and might hamper the efficacy of colistin as alternative therapy in these isolates.