Biotech Health Sci. 2015 August; 2(3): e30748. DOI: 10.17795/bhs-30748 Published online 2015 August 24. Research Article Evaluation of oprD Gene Expression in Carbapenem-Resistant Pseudomonas aeruginosa Strains Isolated From Severe Burn Patients With Secondary Infection Akram Azimi 1 ; Taghi Naserpour 1,* ; Fariba Bazmi 1 ; Amir Peymani 1 ; Masumeh Aslanimehr 1 ; Saman Saadat 1 1 Department of Microbiology, Medical School, Cellular and Molecular Research Center, Qazvin University of Medical Sciences, Qazvin, IR Iran *Corresponding author: Taghi Naserpour, Department of Microbiology, Medical School, Cellular and Molecular Research Center, Qazvin University of Medical Sciences, Qazvin, IR Iran. Tel: +98-91288014010; Fax: +98-2813324971, E-mail: taghin@yahoo.com Received: June 13, 2015; Revised: June 30, 2015; Accepted: July 7, 2015 Background: Pseudomonas aeruginosa is the most common pathogen isolated from severe burn patients with secondary infection. Since high resistance to most types of antibiotics is common among these bacteria, the treatment of infections caused by these agents is very difficult. Loss of oprD proteins from the outer membrane of bacterial cells causes a significant decrease in the sensitivity of Pseudomonas aeruginosa to carbapenems. Objectives: This study was performed to investigate the prevalence of carbapenem-resistant strains of Pseudomonas aeruginosa in burn patients with secondary infection and also to evaluate oprD gene expression as a possible resistance mechanism to carbapenem in isolated carbapenem resistant P. aeruginosa strains. Patients and Methods: One-hundred and eighty-nine clinical isolates of carbapenem resistant Pseudomonas aeruginosa, isolated from burn patients, were identified by microbiological methods followed by determination of antibiotic resistance pattern by the Kirby-Bauer procedure. The expression of oprD gene was determined by quantitative real-time polymerase chain reaction (PCR). Results: Our study showed that 94.2% of the isolates were resistant to imipenem, 99.5% to meropenem, and all were resistant to ertapenem. The OprD gene expression among carbapenem resistant Pseudomonas aeruginosa isolates showed a 2 × 10 -3 to 0.5 times decrease compared to the standard sensitive strain (P < 0.05). Conclusions: The results of this study indicated that a decrease in oprD gene expression is an important mechanism of resistance in carbapenem resistant Pseudomonas aeruginosa isolated from severe burn patients with secondary infection. Keywords: Drug Resistance; OprD; Pseudomonas aeruginosa Copyright © 2015, School of Paramedical Sciences, Qazvin University of Medical Sciences. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the mate- rial just in noncommercial usages, provided the original work is properly cited. 1. Background Pseudomonas aeruginosa are gram negative bacteria dis- tributed in soil, water, skin flora, and the majority of man- made environmental sources, worldwide (1). Regarding the presence of widespread antibiotic resistance among the clinical isolates of P. aeruginosa, this organism is con- sidered as one of the most important bacterial agents as- sociated with nosocomial infections, for which the pro- cess of successful treatment is frequently hard to achieve (2, 3). These bacteria are known as the second most com- mon bacterial agents in burn infections (4, 5) and are also ranked third, after Staphylococcus aureus and Escherichia coli, amongst the most frequent agents of nosocomial infections (6). Pseudomonas aeruginosa is amongst com- mon causes of mechanical ventilation-associated pneu- monia, surgical site infection, hospital-acquired urinary tract infection and bacteremia in patients admitted to in- tensive care units (ICUs) (7, 8). This organism is reported to be the most prevalent pathogen isolated from patients with secondary infection following severe burn injury (9). Currently, the prevalence of hospital Multi-Drug Re- sistance (MDR) strains of P. aeruginosa is increasingly on the rise because of widespread clinical application of antibiotics throughout the world (10), making the treat- ment of infections caused by these MDR organisms very complicated (2, 3). Carbapenems such as imipenem and meropenem are amongst the most important antibacterial agents rou- tinely used in treating infections caused by MDR Pseudo- monas aeruginosa strains (11-13). Generally, controlling the prevalence of these MDR organisms is difficult as P. aeru- ginosa has intrinsic antibiotic resistance against different antibacterial agents (10). There are several mechanisms through which resistance against diverse antibacterial agents occurs by this organism (14). Resistance to differ- ent antibacterial drugs generally occurs either as the result of the combination of different mechanisms in a