Molecular investigation of methicillin-resistant staphylococcus aureus isolates from blood: USA600 emerges as the major type

Introduction: The widespread emergence of methicillin-resistant Staphylococcus aureus is turning into a real worry in public health. The goals of the present study were to identify resistance and virulence encoding genes and molecular characteristics of methicillin-resistant S. aureus bloodstream isolates. Methodology: A cross-sectional study was conducted on 84 S. aureus bloodstream isolates during a 10-month period. To evaluate antibiotic susceptibility of the isolates, we used Kirby-Bauer disk diffusion method. In addition, the prevalence of antimicrobial resistance and toxins genes was assessed using polymerase chain reaction. Isolates were typed according to polymorphisms seven housekeeping genes by MLST. Results: All the isolates were resistant to methicillin. The most prevalent resistance gene was mecA gene (100%) followed by tetM (57.1%), aac (6΄)-Ie/aph (2˝) (53.6%), ant (4΄)-Ia (46.4%), ermA (45.2%), msrA (35.7%), msrB (33.3%), aph (3΄)-IIIa (33.3%), ermB (31%), ermC (16.7%), and mupA (14.3%) genes. The presence of toxin encoding genes tst, pvl, eta, and etb were detected in 25%, 14.3%, 3.6% and 3.6%, respectively. The isolates were classified into five different sequence types: ST45 (29.8%), ST239 (27.4%), ST858 (21.4%), ST22 (17.8%), and ST59 (3.6%). All the high-level mupirocin-resistant (HLMUPR) strains belonged to ST239, while the low-level mupirocin resistant (LLMUPR) strains belonged to ST22 (13%) and ST239 (6%). Conclusions: To the best of our knowledge, the present study is the first report of ST59 in MRSA bloodstream isolates in Iran. Our data demonstrated the need for thorough epidemiological monitoring to detect emergence and dissemination of MDR- MRSA types in our hospitals.