Determination of carbapenem resistance mechanism in clinical isolates of Pseudomonas aeruginosaisolated from burn patients, in Tehran, Iran

Carbapenems are the most important therapeutic options that effect against serious infections caused by multidrug resistant Pseudomonas aeruginosa(MDR-PA) isolates. Carbapenems resistant isolates of P. aeruginosaare increasing worldwide. The aim of this study was to determine the carbapenem resistance mechanisms in clinical P. aeruginosaisolates from burn patients, in Tehran, Iran. A total of 53 nonduplicated isolates of carbapenem-resistant P. aeruginosawere collected from burn patients. The presence of carbapenemase genes were determined by PCR. AmpC overproducer isolates were detected by phenotypic method. The mutation and transcription level of oprDwere determined by PCR-sequencing and quantitative Real-time PCR (RT-PCR), respectively. Twenty-seven (50.9%) isolates were positive for carbapenemase (blaVIM= 25 and blaIMP = 2) and showed high-level resistance to imipenem and meropenem. Twenty-eight isolates were AmpC overproducers. All isolates had a mutation in the oprDgene and down-regulation of oprDwas found in 56.6% of MDR-PA isolates. Although the presence of carbapenemase is the common mechanism of resistant to carbapenem, but carbapenem resistance was found by oprDmutation-driven and the AmpC overproducing isolates in Tehran, Iran.