Molecular epidemiology of nosocomial Staphylococcus aureus in hospitals in different regions of Russia
Staphylococcus aureus is a common human pathogen. In the past few decades, infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have become a global problem. MRSA is resistant to all в-lactam antibiotics, except anti-MRSA cephems, and is one of the main causes of hospital-acquired infections worldwide. The resistance to в-lactams in MRSA is mediated by the presence of mecA gene encoding penicillin-binding protein 2a (PBP2a; also called PBP2) with reduced affinity to в-lactams. The research on MRSA epidemiology is essential for controlling its spread and for delivering therapeutic strategies against life-threatening MRSA infections. In this research we performed molecular typing of 404 nosocomial MRSA isolates collected from adult patients as part of national surveillance studies in Russia in 1998-2008. The strains were selected according to their antibiotic resistance profile, geographic origin and date of isolation. The presence of Panton-Valentine leukocidin (PVL) genes and types of staphylococcal cassette chromosomemec (SCCmec) were determined by means of PCR. Genetic diversity of isolates was assessed with the use of multilocus variable-number tandem repeat analysis(MLVA), staphylococcal protein A (spa) gene sequencing and multilocus sequence typing (MLST). All the strains were PVL-negative. SCCmec type III and type IV cassettes were most prevalent in studied isolates. One isolate carried two copies of mecA gene associated with SCCmec IV and V. By MLVA typing, all the isolates were clustered into 115 types, besides MRSA belonged to distinct clusters. Spa typing and MLST revealed 20 and 6 types respectively. Successful MRSA clones sharing the same MLVA profiles and spa types have been found in geographically distant regions of Russia. The population structure of nosocomial MRSA strains in Russia was therefore clonal and was characterized by expansion of international clones, mainly, ST8-spa type t008-SCCmec IV and ST239-spa type t037-SCCmec III.