The first report of emerging mobilized colistin-resistance (mcr) genes and ERIC-PCR typing in Escherichia coli and Klebsiella pneumoniae clinical isolates in southwest Iran Mojtaba Moosavian,1,2 Nasrin Emam21Infectious and Tropical Diseases Research Center, Health Research Institue, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran; 2Department of Microbiology, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, IranBackground: The emergence of the plasmid-mediated mcr colistin-resistance gene in bacteria poses a potential threat for treatment of patients, especially when hospitalized. The aims of this study were to search for the presence of mcr-1 and mcr-2 genes among colistin-resistant Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) isolates from clinical specimens and to determine the fingerprint of strains by enterobacterial repetitive intergenic consensus sequences PCR (ERIC-PCR) method.Methods: In this study, 712 nonduplicate Enterobacteriaceae isolates from clinical specimens were examined. All of the isolates were subcultured on suitable media, and the isolated colonies were identified by standard biochemical tests. Antimicrobial susceptibility test on 7 antibiotics was performed by disk diffusion method, and minimal inhibitory concentration (MIC) of isolates to colistin was determined by the E-test method. These isolates were typed by ERIC-PCR method, and the presence of mcr-1 and mcr-2 genes was investigated by PCR method.Results: Out of 712 nonduplicate Enterobacteriaceae, 470 isolates, including 351 (74.7%) E. coli and 119 (25.3%) K. pneumoniae, were detected. The results of antibiogram tests showed that most of the isolates (81.3%) were resistant to ceftazidime; however, the most susceptibility among of E. coli and K. pneumoniae isolates was observed (81.5%) to colistin. The typing results by ERIC-PCR method showed 36 and 23 fingerprint patterns for colistin-resistant E. coli and K. pneumoniae strains, respectively. Among 64 (13.6%) colistin-phenotypically-resistant Enterobacteriaceae, 8 isolates (1.7%) had mcr-1 gene. These 8 isolates were attributed to E. coli and K. pneumoniae with 6 and 2 isolates, respectively. Whereas no isolates carrying the mcr-2 gene was found. These colistin-resistant isolates displayed colistin MIC values >2 μg/ml in the antibiotic concentration by E-test method.Conclusion: Spreading of Enterobacteriaceae strains harboring plasmid-mediated mcr could fail the colistin-included therapy regimen as the last line of treatment against multidrug-resistant bacterial infections.Keywords: Enterobacteriaceae; colistin, mcr-1, mcr-2