Prevalence of Genes Involved in Colistin Resistance inAcinetobacter baumannii:First Report from Iraq

Background and Aim:Colistin is increasingly being used as a last-line therapy to treat infections caused by multidrug-resistant (MDR)Acinetobacter baumanniiisolates, when essentially no other options are available in these days. The aim of this study was to detect genes associated with colistin resistance inA. baumannii. Methods:One hundred twenty-one isolates ofA. baumanniiwere collected from clinical and environmental samples during 2016 to 2018 in Baghdad. Isolates were diagnosed asA. baumanniiby using morphological tests, Vitek-2 system, 16SrRNA PCR amplification, and sequencing. Antibiotic susceptibility test was carried out using disk diffusion method. Phenotypic detection of colistin resistance was performed by CHROMagar (TM) COL-APSE medium and broth microdilution method for the determination of the minimal inhibitory concentration. Molecular detection of genes responsible for colistin resistance inA. baumanniiwas performed by PCR. Results:Ninety-two (76%) of the 121A. baumanniiisolates were colistin resistant. Twenty-six (21.5%) of the 121 isolates showed positive growth on CHROMagarAcinetobacterbase for MDR. PCR detectedmcr-1,mcr-2, andmcr-3genes in 89 (73.5%), 78 (64.5%), and 82 (67.8%)A. baumanniiisolates, respectively. Seventy-eight (64.5%) of the 121 isolates harbored the integronintI2gene and 81 (66.9%) containedintI3gene. Moreover, 60 (49.6%) of the 121 isolates were positive for the quorum sensinglasIgene. Conclusion:The presence of a large percentage of colistin-resistantA. baumanniistrains in Baghdad may be due to the presence of mobile genetic elements, and it is urgent to avoid unnecessary clinical use of colistin.