Difference in epidemiology and antibiotic susceptibility of methicillin resistant and methicillin susceptible Staphylococcus aureus isolates.

Background : Antimicrobial resistance of Staphylococcus aureus especially methicillin resistant S. aureus (MRSA) continues to be a problem for clinicians worldwide. Although difference in epidemiology and antibiotic susceptibility of methicillin resistant S. aureus (MRSA) and methicillin susceptible S. aureus (MSSA) isolates has been proposed by investigators, few data have been reported to now. Patients and methods : Disk diffusion method was used for determination of in vitro susceptibility of S. aureus isolates to 15 antibiotics. Susceptibility pattern of 192 non-duplicates S. aureus isolated from clinical specimens in four university hospitals in Tehran, from November 2007 to August 2008, were compared. In addition, distribution of MRSA and MSSA isolates were investigated in different specimens, on various wards, and in different age groups. Results : MRSA isolates were constituted 49% of all isolates. While only 1.7% of the MSSA isolates were multidrug resistant, all of MRSA were shown resistance to at least five antibiotics. Majority of isolates from patients ≥65 years old were MRSA and prevalence of methicillin resistance was highest among S. aureus isolated from respiratory specimens. Also, MRSA appeared to be more prevalent in intensive care units and operation wards than in other departments. Conclusion : This study has shown a relationship between methicillin resistance and resistance to other antibiotics in S. aureus isolates. Also, considerable differences were observed in epidemiology of MRSA and MSSA isolates.