Molecular Characterization and Antimicrobial Susceptibility Patterns of Methicillin-Resistant Staphylococcus aureus Isolates in Tabriz, Northwest of Iran

Methicillin resistant Staphylococcus aureus (MRSA) are one of the most common and important pathogens, accounting for diverse nosocomial and community-acquired infections. The serious concern about these bacteria is the development of antibiotic resistance.
The present study was conducted to investigate the frequency of MRSA strains, their epidemiological and molecular relationships and antibiotic susceptibility patterns of isolated strains from university teaching hospitals of Tabriz, Northwestern Iran (during years 2014 and 2015).
A total of 215 non-repetitive clinical isolates of S. aureus were identified using standard methods. The MRSA isolates were detected by the combination of phenotypic and genotypic methods. The presence of pvl gene and SCCmec types was determined by PCR and multiplex PCR, respectively. The MRSA isolates, in which the presence of mecA gene had been confirmed by PCR, were subjected to Rep-PCR analysis. Resistance to antibacterial agents was determined by disk diffusion, screening agar, and E-test methods.
All S. aureus isolates were positive for nuc gene and 87 (40.5%) of them revealed the presence of mecA gene, confirming them as MRSA. All isolates were found to be sensitive to linezolid and vancomycin. However, a reduced sensitivity of 3 MRSA isolates to vancomycin was observed (MIC = 6 μg/mL). SCCmec type III was the most prevalent (79.31%), followed by type IVd (13.80%) and type I (6.90%). The PVL occurrence was detected in 33 (15.35%) S. aureus isolates. The MRSA isolates could be divided to 2 main clusters, indicating the possible clonal relatedness of MRSA isolates.
The MRSA isolates with SCCmec type III were the predominant MRSA strains in this area. The majority of MRSA isolates were MDR. Linezolid and vancomycin were found as suitable antibiotics for the treatment of MRSA. The results of typing methods indicated possible clonal relatedness among MRSA isolates. Therefore, routine infection control surveillance is necessary for the prevention of epidemic emergence.