Evaluation of oprD Gene Expression in Carbapenem-Resistant Pseudomonas aeruginosa Strains Isolated From Severe Burn Patients With Secondary Infection

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.