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Characterization of the staphylococcal cassette chromosome mec insertion site in 108 isolates lacking the mecA gene and identified as methicillin-resistant Staphylococcus aureus by the Xpert MRSA assay

Stojanov, M. ; Blanc, D.

In: European Journal of Clinical Microbiology & Infectious Diseases, 2014, vol. 33, no. 11, p. 1967-1971

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    Titre
    • Characterization of the staphylococcal cassette chromosome mec insertion site in 108 isolates lacking the mecA gene and identified as methicillin-resistant Staphylococcus aureus by the Xpert MRSA assay
    Auteur
    • Stojanov, M.. Hospital Preventive Medicine Service, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland
    • Blanc, D.. Hospital Preventive Medicine Service, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland
    Type de document
    • Postprint
    Langue
    • Inglese
    Publié dans
    • European Journal of Clinical Microbiology & Infectious Diseases, 2014, vol. 33, no. 11, p. 1967-1971. Springer Berlin Heidelberg
    Autre version électronique
    Classification
    • Santé
    Identifiant OAI-PMH
    • oai:doc.rero.ch:325865
    Summary
    During a 3-year period, 848 patients were detected as carriers of methicillin-resistant Staphylococcus aureus (MRSA) by the Xpert MRSA assay (Cepheid). Among them, 108 patients (12.7%) were colonized with strains showing methicillin-susceptible phenotypes and absence of the mecA gene, despite being positive with the rapid polymerase chain reaction (PCR) assay. DNA sequences of the staphylococcal cassette chromosome mec (SCCmec) insertion site of these "false-positive” strains was determined by direct sequencing of the genomic DNA. More than half (53.7%) of the strains had DNA sequences unrelated to either SCC or SCCmec and one-third had DNA sequences related to non-mec SCC. Only 10.2% of the strains carried sequences related to SCCmec, suggesting that a sequence containing the mecA gene was lost from an SCCmec. These findings differ from the general idea that all methicillin-susceptible S. aureus having positive Xpert MRSA assay results are essentially MRSA that lost the mecA gene.