Background and Aims: Staphylococcus aureus as a�Gram- positive coccus causes a variety of infections in humans. It is one of the infectious agents in hemodialysis patients. Those patients who carry this organism at their nose are exposed to infection and possible morbidity and mortality due to this bacterium. Resistance to antibiotics in staphylococci is increasing. Resistance development is due to mutation and by plasmid DNA transmission. The aim of this study was to determine plasmid profile and antibiotic resistance of Staphylococcus aureus strains isolated from nasal carriers in dialysis patients in Imam Khomeini Medical Center. Susceptibility testing to antibiotics, plasmid extraction and analysis and epidemiologic relationship of these isolates were investigated.�

  Methods: In this study nasal specimens of 107 patients in dialysis ward of Imam Khomeini Medical Center were collected and cultured on blood agar plates. The colonies were identified as S.aureus strains. The susceptibility of 50 strains isolated from the patients against 12 antibiotics were tested using Kirby- Bauer standard method. A standard S.aureus strain (ATCC29213) was used to control quality of antibiotic discs. The isolates were cultured on LB medium and plasmid DNAs were extracted and electrophoresed on agarose gel using Parisi et al method.

  Results : The results of resistance rate against 12 used antibiotics were as follows: resistance of the strains against gentamicin, oxacillin, neomycin, clindamycin, erythromycin, cotrimoxazole, choloramphenicole, tetracycline, and ciprofloxacin were 20%, 28%, 30%, 26%, 30%, 44%, 32%, 36%, and 10%, respectively. All of the strains were resistant to amoxycillin and penicillin and none of them were resistant to vancomycin. Of 50 S. aureus strains, only 27 strains contained plasmid DNA. Most of the strains revealed a big plasmid. Plasmid profiles of the strains will be presented.

  Discussion: Our results showed that there was a close relationship between high resistance to antibiotics and presence of plasmids in S. aureus strains. Similarities among resistance to antibiotics and plasmid profiles in our strains isolated from the same ward showed that these strains were from the same sources and indicated a unique clonal possibility. The resistance to antibiotics of the strains lacking plasmids could be from choromosomal resistance

  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.