Diversity of SCCmec elements and spa types in South African Staphylococcus aureus mecA-positive blood culture isolates.

Background: The prevalence of Staphylococcus aureus varies depending on the healthcare facility, region and country. To understand its genetic diversity, transmission, dissemination, epidemiology and evolution in a particular geographical location, it is important to understand the similarities and variations in the population being studied. This can be achieved by using various molecular characterisation techniques. This study aimed to provide detailed molecular characterisation of South African mecA-positive S. aureus blood culture isolates by describing the SCCmec types, spa types and to lesser extent, the sequence types obtained from two consecutive national surveillance studies.

Methods: S. aureus blood culture isolates from a national laboratory-based and enhanced surveillance programme were identified and antimicrobial susceptibility testing was performed using automated systems. A real-time PCR assay confirmed the presence of the methicillin-resistance determinant, mecA. Conventional PCR assays were used to identify the SCCmec type and spa type, which was subsequently analysed using the Ridom StaphType™ software. Multilocus sequence typing was performed on selected isolates using conventional methods. MRSA clones were defined by their sequence type (ST), SCCmec type and spa type.

Results: A detailed description of findings is reported in this manuscript. SCCmec type III predominated overall followed by type IV. A total of 71 different spa types and 24 novel spa types were observed. Spa type t037 was the most common and predominated throughout followed by t1257. Isolates were multidrug resistant; isolates belonging to all SCCmec types were resistant to most of the antibiotics with the exception of type I; isolates with spa type t045 showed resistance to all antibiotics except vancomycin. The most diverse SCCmec-spa type complex was composed of the SCCmec type IV element and 53 different spa types.

Conclusion: Although ST data was limited, thereby limiting the number of clones that could be identified, the circulating clones were relatively diverse.