In compliance with KFMC IC & EH policy, each patient is screened for MRSA prior to hospital admission by PCR using the BD GenOhm MRSA assay according to manufacturer’s instructions (Becton Dickinson, USA). Patients were isolated in wards according to MRSA PCR results and all PCR-positive samples were cultured. Isolates for the

study were collected between summer 2010 and spring 2011. Sample types for the respective isolates are listed in the Additional file 1. Five isolates related to environmental swabbing of areas near patients which were considered as potential sources of infection. Seven isolates (six from nasal swabs and one from sputum, see the Additional file 1) originated from screening samples. Another six isolates came from nasal and oral swabs taken during diagnostic procedures. The remaining isolates included 50 from swabs AZD9291 from skin lesions, abscesses etc., 15 from blood cultures, Transferase inhibitor nine from respiratory samples, two from urines, two from drains and one from cerebrospinal fluid. For ten isolates, data could not be retrieved. Isolates were subjected to antimicrobial microbial susceptibility testing (Becton Dickinson Phoenix, USA, according to Clinical & Laboratory Standards Institute guidelines) and submitted for array-based MRSA typing to the Faculty of Medicine, Dresden, Germany. Approval from the KFMC Institutional Review

Board was obtained to use patient isolates for this study. Individual patient´s consent was not sought as isolates were derived from routine diagnostics and as data were processed anonymously. Copy strains, i.e., multiple isolates from one individual patient were excluded from further analysis unless they differed in array hybridisation profiles. This was the case for four individual patients. Array procedures For characterisation of isolates, the StaphyType DNA microarray (Alere Technologies GmbH, Jena, Germany) was used. This DNA microarray covers ca. 170 genes

and their allelic variants. This includes species markers, typing markers (SCCmec, capsule Rebamipide and agr group), resistance genes as well as genes encoding exotoxins and adhesion factors. A list of the included target genes as well as primer and probe sequences have been published previously [20, 21]. Procedures were performed according to protocols as recommended by the manufacturer and as previously published [20, 21]. In short, MRSA were cultured on Columbia blood agar, harvested and enzymatically lysed prior to DNA preparation using an MK5108 automated system (EZ1, Qiagen, Hilden, Germany). The purified DNA was used as template in a linear primer elongation reaction during which biotin-16-dUTP was incorporated into the resulting amplicons. Reaction products were hybridised to the microarray. After washing and blocking, horseradish-peroxidase-streptavidin conjugate was added which bound to the biotin labels. After further incubation and washing, a dye was added which locally precipitated in presence of the peroxidase.