Molecular Characterization of Methicillin and Vancomycin Resistant Staphylococcus aureus Strains Isolated from Hospitalized Patients.

OBJECTIVES: Nosocomial infections caused by methicillin resistant Staphylococcus aureus (MRSA) and emergence of vancomycin resistant S. aureus (VRSA) have led to great concern in healthcare settings worldwide.

METHODS: A total of 100 S. aureus clinical isolates from hospitalized patients were investigated for antimicrobial susceptibility, the presence of resistance (mecA, vanA, and vanB) and virulence (hlaA, fnbpA, cna, clfA, tsst-1, eta, and spa) encoding genes, and molecular typing based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of spa gene.

RESULTS: All isolates were resistant to one or more antibiotics, with the most frequent resistance found against amoxicillin (69%). A total of 46 isolates were MRSA, and 40% of isolates were multidrug resistant (MDR). Of all S. aureus isolates, two isolates were confirmed as VRSA and four isolates confirmed as vancomycin intermediate S. aureus (VISA). The frequency of clfA, cna, tsst-1, and eta genes among MRSA isolates was significantly higher than methicillin sensitive S. aureus (MSSA). The significant correlation between MDR isolates and the carriage of multiple virulence genes was seen. All MDR isolates carried at least four virulence genes. Furthermore, biofilm formation in MRSA isolates was significantly higher than MSSA. The spa gene PCR products generated 4 major and 10 minor types. After digestion of spa amplicons with HindIII restriction enzyme, 10 different patterns ranging 174-938 bp were detected. S2b and S2a subtypes were detected frequently in MRSA isolates.

CONCLUSIONS: It seems that the appropriate surveillance and control measures are essential to prevent the emergence and transmission of MRSA and VRSA strains in our country.