Investigating a rare methicillin-resistant Staphylococcus aureus strain: first description of genome sequencing and molecular characterization of CC15-MRSA Abiola C Senok,1 Ali M Somily,2 Peter Slickers,3,4 Muhabat A Raji,5 Ghada Garaween,5 Atef Shibl,5 Stefan Monecke,3,4,6 Ralf Ehricht3,4 1Department of Basic Science, College of Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates; 2Department of Pathology and Laboratory Medicine, College of Medicine, King Khalid University Hospital and King Saud University, Riyadh, Saudi Arabia; 3Alere Technologies GmbH, Jena, Germany, 4InfectoGnostics Research Campus, Jena, Germany; 5Department of Microbiology and Immunology, College of Medicine, Alfaisal University, Riyadh, Saudi Arabia; 6Institute for Medical Microbiology and Hygiene (IMMH), Technische Universität Dresden, Dresden, Germany Purpose: Methicillin resistant Staphylococcus aureus CC15 strains (CC15-MRSA) have only been sporadically described in literature. This study was carried out to describe the genetic make-up for this rare MRSA strain.Methods: Four CC15-MRSA isolates collected in Riyadh, Saudi Arabia, between 2013 and 2014 were studied. Two isolates were from clinical infection and 2 from retail meat products. Whole genome sequencing was carried out using Illumina HiSeq2500 genome analyzer.Results: All the CC15-MRSA isolates had the multilocus sequence typing profile ST1535, 13–13-1–1-81-11-13, which is a single locus variant of ST15. Of the 6 contigs related to the SCC element, one comprised a recombinase gene ccrAA, ccrC-PM1, fusC and a helicase, another one included mvaS, dru, mecA and 1 had yobV and Q4LAG7. The SCC element had 5 transposase genes, namely 3 identical paralogs of tnpIS431 and 2 identical paralogs of tnpIS256. Two identical copies of a tnpIS256-based insertion element flank the aacA-aphD gene. Two copies of this insertion element were present with 1 located in the SCC element and another inserted into the sasC gene. A short 3 kb region, which lacks any bacteriophage structural genes and site-specific DNA integrase, was inserted into the hlb gene. The hsdM and the 5’-part of the hsdS gene are replaced by a copy of the hsdM/hsdS paralogs from nSab giving rise to a new chimeric paralog of hsdS in vSaa.Conclusion: CC15-MRSA shows a novel SCCmecV/SCCfus composite element. Its variant of hsdM/hsdS probably facilitated uptake of foreign mobile genetic elements that promoted emergence of CC15-MRSA. Close surveillance is needed to monitor spread and emergence of further CC15 MRSA strains. Keywords: whole genome sequencing, MRSA, MLST, clonal complex, SCCmec, Saudi Arabia