Staphylococcal cassette chromosome mec (SCCmec) analysis and antimicrobial susceptibility patterns of methicillin-resistant Staphylococcus aureus (MRSA) isolates in Tehran, Iran

Oxacillin resistance was present in 99 of 277 (36%) consecutive Staphylococcus aureus Isolates collected from hospital patients in Tehran during a 15-month period (January 2004-March 2005). The majority of isolates (77/99 = 78%) had been cultured from wounds or blood. The staphylococcal cassette chromosome mec (SCCmec) types and antimicrobial susceptibility patterns of 99 methicillin-resistant S. aureus (MRSA) strains were determined. Disk diffusion and agar dilution methods were used to determine the susceptibility of isolates to antimicrobial agents as instructed by Clinical and Laboratory Standards Institute. The presence of mecA and SCCmec types was determined by PCR and multiplex PCR. All MRSA isolates were susceptible to vancomycin (MIC90 <= 2 mu g/ml), teicoplanin (MIC90 <= 2 mu g/ml), linezolid, and tigecycline. SCCmec types 111, IIIA, and IV were detected in 87%, 11%, and 2% of isolates, respectively. Isolates belonging to SCCmec types III and IIIA were multiresistant; in addition to P-lactam resistance, at least 95% of them were also resistant to kanamycin, erythromycin, tetracycline, azithromycin, gentamicin, and ciprofloxacin. These data indicate that SCCmec type III MRSA isolates frequently infect patients in a university hospital in Tehran. Susceptibility of MRSA isolates to linezolid and tigecycline suggests that these drugs could play an important role in the treatment of infections caused by these multiresistant pathogens.