Background and Objectives: Pseudomonas aeruginosa is a nosocomial pathogen that presents high antibiotic resistance.There are phenotyping and genotyping methods for epidemiologic study of Pseudomonas aeruginosa such as antibiotic resistance pattern and plasmid profile analysis. Plasmid analysis provides useful information concerning the source of the strains and number of clones present in the epidemies. Thus, this study was conducted to evaluate antibiotic and plasmid profiles of P. aeruginosa strains isolated from in-patients of the Sina Medical Centre of Tabriz to clarify epidemyological correlation among isolated strains.

  Methods: During 13 months, 135 strains of P. aeruginosa were isolated from different infections in hospitalized patients at Sina Medical Center of Tabriz. Antibiotic susceptibility tests were performed using disc agar diffusion test. For plasmid DNA extraction and detection of open circular bands from supercoiled ones, modified alkaline lysis procedure and two dimensional electrophoresis were used, respectively. Enzymatic digestion of plasmids was carried out by EcoRI and HincII restriction enzymes.

  Results: Resistance rates of strains against antibacterial agents were recorded as: Aztreonam (77%), colistin (74%), ceftazidime (69%), pipracillin (67%), ofloxacin (62%), tobramycin (56%), carbenicillin (54%), gentamicin (51%), ciprofloxacin (22%), amikacin (15%), polymixin B (13%) and imipenem (2%). Plasmid profiles of our test strains revealed that only 67 strains harbored plasmid(s). Number of isolated plasmids ranged 1-6 in each strain with molecular mass of 0.5kb-21kb. When the isolated plasmids were digested using restriction endonuclease enzymes (EcoRI and HincII), in 32% of them similar digestion profiles were obtained by EcoRI indicating a unique source for them.

  Conclusion : Our findings suggest high antibiotic resistance and plasmid presence in P. aeruginosa strains isolated from different infections, and there were remarkable similarities among isolated plasmids. Since our test strains had been isolated from various wards in a short period of time, the results raise the possibility of unique source for some strains or high prevalence of genetic exchange among P. aeruginosa strains.