Detection and characterisation of SCCmec remnants in multiresistant methicillin-susceptible Staphylococcus aureus causing a clonal outbreak in a Swedish county
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The purpose of this study was to investigate if multiresistant methicillin-susceptible Staphylococcus aureus (MR-MSSA) causing a clonal outbreak in Östergötland County, Sweden, were derived from methicillin-resistant S. aureus (MRSA) by carrying remnants of SCCmec, and, if so, to characterise this element. A total of 54 MSSA isolates with concomitant resistance to erythromycin, clindamycin and tobramycin from 49 patients (91% clonally related, spa type t002) were investigated with the BD GeneOhm MRSA assay and real-time polymerase chain reaction (PCR) targeting the SCCmec integration site/SCCmec right extremity junction. DNA sequencing of one isolate representing the MR-MSSA outbreak clone was performed by massive parallel 454 pyrosequencing. All isolates that were part of the clonal outbreak carried SCCmec remnants. The DNA sequencing revealed the carriage of a pseudo-SCC element 12 kb in size, with a genomic organisation identical to an SCCmec type ΙΙ element, except for a 41-kb gap. This study demonstrates the presence of a pseudo-SCC element resembling SCCmec type II among MR-MSSA, suggesting possible derivation from MRSA. The presence of SCCmec remnants should always be considered when SCCmec typing is used for MRSA detection, and may not be suitable in locations with a high prevalence of MR-MSSA, since this might give a high number of false-positive results.
KeywordsmecA Gene SCCmec Type PFGE Pattern Polymerase Chain Reaction Reaction Mixture MSSA Isolate
S. aureus control strains were kindly provided by Teruyo Ito, Juntendo University, Tokyo, Japan, and Anna Shore, Trinity College, Dublin, Ireland. We thank Andreas Matussek, Ryhov Hospital, Jönköping, Sweden, for providing us with the modified MREJ protocol. We also thank the 454 node at the Norwegian Sequencing Centre, Oslo University, Norway, for performing the 454 pyrosequencing. A final thank you goes to the Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD USA (the IGS Annotation Engine), for the help with the annotation of the ECT-R 2 complete genome sequence.
This work was supported by the Östergötland County Council and the Scandinavian Society for Antimicrobial Chemotherapy (SSAC) (grant number 2009-22495).
This study was approved by the Regional Ethical Review Board in Linköping, Sweden.
Conflict of interest
The authors declare that they have no conflict of interest.
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