Background: Agr systems, is responsible for control and coordination in production of virulence factors, exotoxins secretory and hemolysins in Staphylococcus aureus. The aim of this study was to determine and identify the frequency of agr genes in susceptible and methicillin-resistant Staphylococcus aureus strains in clinical samples and carriers employed in remedial centers.

Materials and Methods: This descriptive study was done among a total of 200 strains of Staphylococcus aureus isolated from clinical samples and healthy carriers in Hamadan. Antibiotic susceptibility pattern of all isolates was determined by disk diffusion methods. After DNA extraction, the presence of mecA and agr genes was investigated using PCR. SPSS software package version 20 was used to perform statistical tests.

Results: All 200 Staphylococcus aureus strains were susceprible to vancomycin. The prevalence of mecA was 50%. The PCR results showed that agrA was the most perevalent gene followed by the agrC in all isotated Staphylococcus aureus strains. None of the isolates harbored the agrB and agrD gene.

Conclusion: Pathogenesis of Staphylococcus is dependent on some proteins other superficial or excreted which under controlling of agr system. In the present study, the feequency of agrA gene in the methicillin-resistant strains, methicillin-sensitive strains isolated from clinical samples and carriers employed in remedial centers was higher than the other agr types. Therefore, presumably, agrA gene plays an important role Staphylococcal infections.