Background: Staphylococcus aureus is considered a common pathogenic factor in infections. Increase in infections caused by this bacterium in developing countries has led to many problems. The aim of this study is to identify the antibiotic patterns of methicillin-resistant Staphylococcus aureus isolated from patients in the central hospital of Arak.

Materials and Methods: In this descriptive cross-sectional study, a total of 100 samples were isolated from hospital patients during one year. The isolates sensitivity to cefoxitin and oxacilin disks were evaluated through disk diffusion. Using polymerase chain reaction (PCR), the isolates were tested for the presence of mecA gene. Finally, antibacterial resistance patterns of the isolates to 13 antibiotics were determined.

Results: In this study, 80 samples in a total of 100 isolates of Staphylococcus aureus were methicillin-resistant. Evaluation and assessment of antibiotic resistance showed the greatest resistance to penicillin (100%), tetracycline (88.50%), levofloxacin (85.70%), and ciprofloxacin (85.70%), respectively, while the lowest levels of resistance were observed to antibiotics chloramphenicol (5.70%), netilmicin (5.70%), and mupirocin (0%), respectively.

Conclusion: This study showed increased resistance to different antibiotics in Staphylococcus aureus that is a serious warning to the treatment of infections caused by this bacterium in the region. Therefore, in order to prevent increased resistance to other antibiotics, it is essential to withhold prescriptions and unessential use of available antibiotics.

Background: Pseudomonas aeruginosa is one of the most common nosocomial pathogens with high mortality rates. OprD is the major resistance mechanism to carbapeneme antibiotics. The aim of this study was to determine the expression of the genes encoding these efflux pumps using qRT-PCR.

Materials and Methods: This study examined 100 strains of Pseudomonas aeruginosa isolated from patients admitted to various hospitals in the Hamedan. Conventional phenotypic tests were used for identifying the 100 collected samples, then 31 samples were selected based on type of collected specimen and antibiotic susceptibility test i.e. antibiotic disk diffusion method performed for aminoglycoside, quinolone and carbapenem antibiotics. Furthermore, MIC method was performed for imipenem. Finally, RNA was extracted and converted to cDNA for determining the efflux pump genes expression using qRT-PCR.

Results: Among 8 selected antibiotics, the greatest resistance was for levofloxacin (61.2%, n=19) and the lowest one for imipenem (9.6%, n=3). The results of MIC were to imipenem 12 samples (38.7%) resistant, 13 samples (41.93%) intermediate, and 6 samples (19.35%) sensitive. The OprD gene was present in all strains but different expression has been observed. The strains with over expression of OprD gene showed high sensitivity towards carbapenems family antibiotics especially imipenem.

Conclusion: Identifying of bacterial resistance mechanisms is very complicated and extensive due to different mechanisms involved for similar antibiotics. OprD is main cause of attachment to the carbapenems family antibiotics. The more expression of OprD shows the more antibiotic sensitivity.