Ahmad Farajzadeh Sheikh - Department of Microbiology, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran|Health Research Institute, Infectious and Tropical Diseases Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz,
Mojtaba Shahin - Department of Microbiology, Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran|Health Research Institute, Infectious and Tropical Diseases Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz,
Leili Shokoohizadeh - Department of Microbiology, Faculty of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
Mehrdad Halaji - Department of Microbiology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

Objective(s): Resistance to carbapenems is the principal reason for the continuing utilization of colistin as a last resort choice for treating the infections resulted from multidrug carbapenem-resistant Pseudomonas aeruginosa (CRPA) isolates. The assessment of antimicrobial resistance pattern, the prevalence of carbapenem-resistance determinants, and molecular epidemiology of colistin-resistant isolates among CRPA strains were the aims of the present research. Materials and Methods: The current cross-sectional research was conducted on 269 CRPA isolates collected from various clinical samples from 2013 to 2016. After performing identification tests, disk diffusion as well as MIC methods were used for testing sensitivity to the antibiotics. Modified Hodge Test (MHT) was utilized to produce carbapenemase. PCR technique identified beta-lactamase classes A, B, and D genes. Results: In total, from 269 CRPA, five isolates (1.3%) were resistant to colistin. It was found that blaNDM-1, blaIMP-1, blaVIM-2, and blaOXA-10 genes were present in 40%, 40%, 20%, and 100% of colistin-resistant isolates, respectively. DLST type 25-11 is a significant cluster of colistin-resistant P. aeruginosa isolates. Conclusion: The appearance of colistin-resistant isolates in CRPA carrying blaNDM-1 with multiple carbapenem-resistant genes shows the great problem in the treatment of P. aeruginosa infections.

Colistin, Double-locus sequence typing, Drug resistance, Pseudomonas aeruginosa