Prevalence of Genes Involved in Colistin Resistance in <i>Acinetobacter baumannii:</i> First Report from Iraq

Abstract

<b><i>Background and Aim</i></b><i>:</i> Colistin is increasingly being used as a "last-line" therapy to treat infections caused by multidrug-resistant (MDR) <i>Acinetobacter baumannii</i> isolates, when essentially no other options are available in these days. The aim of this study was to detect genes associated with colistin resistance in <i>A. baumannii</i>. <b><i>Methods:</i></b> One hundred twenty-one isolates of <i>A. baumannii</i> were collected from clinical and environmental samples during 2016 to 2018 in Baghdad. Isolates were diagnosed as <i>A. baumannii</i> by 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™ COL-APSE medium and broth microdilution method for the determination of the minimal inhibitory concentration. Molecular detection of genes responsible for colistin resistance in <i>A. baumannii</i> was performed by PCR. <b><i>Results:</i></b> Ninety-two (76%) of the 121 <i>A. baumannii</i> isolates were colistin resistant. Twenty-six (21.5%) of the 121 isolates showed positive growth on CHROMagar <i>Acinetobacter</i> base for MDR. PCR detected <i>mcr-1</i>, <i>mcr-2</i>, and <i>mcr-3</i> genes in 89 (73.5%), 78 (64.5%), and 82 (67.8%) <i>A. baumannii</i> isolates, respectively. Seventy-eight (64.5%) of the 121 isolates harbored the integron <i>intI2</i> gene and 81 (66.9%) contained <i>intI3</i> gene. Moreover, 60 (49.6%) of the 121 isolates were positive for the quorum sensing <i>lasI</i> gene. <b><i>Conclusion:</i></b> The presence of a large percentage of colistin-resistant <i>A. baumannii</i> strains in Baghdad may be due to the presence of mobile genetic elements, and it is urgent to avoid unnecessary clinical use of colistin.