Molecular epidemiology and carbapenem resistance of Pseudomonas aeruginosa isolated from patients with burns

Objective: The aim of this study was to investigate the molecular epidemiology and carbapenem resistance mechanisms of Pseudomonas aeruginosa isolated from patients with burns in Azerbaijan, Iran. Method: Pseudomonas aeruginosa was isolated from 38 patients with burns. Disk diffusion and agar dilution methods were used to determine antibiotic susceptibility patterns. The overproduction of AmpC beta-lactamase and efflux pumps were detected by phenotypic methods. The presence of carbapenemase-encoding genes was detected by multiplex polymerase chain reaction (PCR). Expression of the OprD gene and MexAB efflux pumps were also evaluated with real-time PCR. Random amplified polymorphic DNA typing (RAPD-PCR) was used for genotyping of carbapenem-resistant Pseudomonas aeruginosa (CRPA). Results: Minimum inhibitory concentration (MIC) assays demonstrated high levels of resistance to all classes of antibiotics except colistin and polymyxin B. The initial screening by carbapenem disks indicated 24 isolates (63.15%) as CRPA. Different mechanisms of carbapenem resistance were observed, including carbapenemase production (8.4%), overexpression of AmpC (25%) and decreased expression of OprD (75%). The overexpression of MexAB efflux pumps was detected in 19 (79.1%) isolates by phenotypic assay or real-time PCR. The resistance to carbapenem was multifactorial in most cases (58.3%). The RAPD genotyping revealed different patterns with nine clusters. Conclusion: According to our results, the prevalence of CRPA is at an alarming level. Our results did not demonstrate an epidemic clone. The most common mechanism of carbapenem resistance was decreased expression of OprD. Therefore, we suggest a reconsideration in the management of CRPA infections of patients in our burn care hospital in Azerbaijan, Iran.