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Updated: Aug 8, 2026

Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
09:03

Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus

Published on: September 5, 2013

Novel mobile variants of staphylococcal cassette chromosome mec in Staphylococcus aureus

W T M Jansen1, M M Beitsma, C J Koeman

  • 1University Medical Center Utrecht, Eijkman Winkler Center for Medical Microbiology and Infectious Diseases, The Netherlands. W.T.M.Jansen@azu.nl

Antimicrobial Agents and Chemotherapy
|May 26, 2006
PubMed

Insights

Staphylococcal cassette chromosome mec type IV (SSCmec IV) excises spontaneously, facilitating horizontal transfer in methicillin-resistant Staphylococcus aureus (MRSA). This genetic plasticity, driven by recombinase activity, contributes to MRSA evolution.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Staphylococcal cassette chromosome mec type IV (SSCmec IV) is linked to virulent community-acquired methicillin-resistant Staphylococcus aureus (MRSA).
  • Horizontal transfer of SCCmec elements contributes to the spread of antibiotic resistance in staphylococci.
  • Understanding the mechanisms of SCCmec excision is crucial for controlling MRSA dissemination.

Purpose of the Study:

  • To investigate the mechanism of ccrA/B type 2 recombinase-mediated excision of SCCmec IV and SCCmec II.
  • To identify alternative excision products of SCCmec IV and their genetic characteristics.
  • To explore the role of SCCmec excision in the genetic plasticity and horizontal transfer of MRSA.

Main Methods:

  • Studied spontaneous and recombinase-induced excision of SCCmec IV (5 strains) and SCCmec II (2 strains).
  • Introduced ccrA/B type 2 recombinase genes under a bacterial phage promoter.
  • Sequenced alternatively excised products from SCCmec IV strains.

Main Results:

  • Spontaneous SCCmec IV excision was observed, but not in SCCmec II strains.
  • Excision of SCCmec II and multiple SCCmec IV variants occurred upon introduction of ccrA/B type 2.
  • Identified a shortened SCCmec' variant and a conserved SCC-like element lacking mecA and recombinases.
  • Excision of the SCC-like element was SCCmec-dependent and could occur separately or with SCCmec.

Conclusions:

  • The ccrA/B type 2 recombinase mediates diverse excision events of SCCmec IV, including a novel composite cassette.
  • The variety and abundance of SCCmec IV excisions likely contribute to horizontal transfer and genetic plasticity in MRSA.
  • The identified SCC-like element represents a mobile genetic element potentially involved in MRSA evolution.

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