High prevalence of direct repeat unit types of 10di, 8 h and 8i among methicillin resistant Staphylococcus aureus strains with staphylococcal cassette chromosome mec type IIIA isolated in Tehran, Iran

The emergence of methicillin-resistant (MRSA) is a main concern in burn care centers worldwide. The some reports of MRSA in Iran suggested that MRSA with type SCC III is common among burn patients. The aim of this study was to determine the prevalence, virulence genes, and antimicrobial susceptibility of the direct repeat units ( ) types of MRSA with SCC IIIA isolated from burn wounds in a burn care center in Tehran, Iran. In total, 165 isolates were collected from clinical samples. In order to detect MRSA isolates, the A gene was amplified through the polymerase chain reaction (PCR) method. Antimicrobial susceptibility was tested using the disc agar diffusion test. Moreover, the PCR method was applied to determine SCC types, virulence genes, and antimicrobial resistance genes. The region was sequenced and thereby, types and repeats were identified. A similarity matrix was used to create minimum spanning tree (MST). The prevalence of MRSA was 69% (114 out of 165 isolates). Most of MRSA isolates (61 out of 114, 53.5%) were SCC type IIIA. All MRSA isolates were vancomycin-susceptible and more than 68% of MRSA isolates with SCC type IIIA were mupirocin resistant. The successful typing of isolates with SCC type IIIA revealed fourteen different types. There were two new types, namely dt10di and dt7aj. MST analysis indicated the presence of the three clusters of dt10di (cluster I), dt8i-dt8 h (cluster II), and dt11c-dt10ao-dt11dd-dt11a-dt10a (cluster III). There were significant differences between clusters I and II respecting antimicrobial resistance pattern and virulence genes. Three main clusters are prevalent in the study setting. The main types in the setting are dt10di, dt8i, and dt8 h. typing can be used to differentiate MRSA strains with SCC IIIA.