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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

A subset of Staphylococcus aureus strains harboring staphylococcal cassette chromosome mec (SCCmec) type IV is

Michael J Noto1, Gordon L Archer

  • 1Department of Microbiology, Virginia Commonwealth University School of Medicine, Richmond, VA 23298-0565, USA.

Antimicrobial Agents and Chemotherapy
|July 28, 2006
PubMed

Insights

The staphylococcal cassette chromosome mec (SCCmec) type IV element

Area of Science:

  • Microbiology
  • Genetics
  • Molecular Biology

Background:

  • The staphylococcal cassette chromosome mec (SCCmec) is a mobile genetic element carrying the mecA gene, responsible for methicillin resistance in staphylococci.
  • SCCmec is classified into five major isotypes based on the presence of recombinase genes (ccrAB or ccrC).
  • SCCmec type IV is hypothesized to be mobile, contributing to the spread of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections.

Purpose of the Study:

  • To investigate the chromosomal excision of SCCmec type IV, the initial step in its mobility.
  • To determine if recombinase activity is conserved across different SCCmec types and strains.

Main Methods:

  • Analysis of recombinase genes (ccrAB) in Staphylococcus aureus and Staphylococcus epidermidis strains.
  • Assessment of the ability of CcrAB recombinases to catalyze the excision of SCCmec types I, II, and IV from the chromosome.
  • Investigation of genetic elements associated with SCCmec integration stability.

Main Results:

  • CcrAB recombinases successfully catalyzed the excision of SCCmec types I and II in tested strains, demonstrating conserved activity despite amino acid variations.
  • Excision of SCCmec type IV was not observed in all strains, particularly in a subset of highly related S. aureus strains.
  • The inability to excise SCCmec type IV in these strains correlated with the insertion of a mobile element carrying the staphylococcal enterotoxin H (seh) gene downstream of SCCmec.

Conclusions:

  • The mobility of SCCmec type IV is not universal and can be hindered by specific chromosomal integrations.
  • The insertion of mobile elements, such as the one carrying seh, can stabilize SCCmec integration, potentially impacting the dissemination of methicillin resistance.
  • Understanding SCCmec excision mechanisms is crucial for controlling the spread of antibiotic resistance in staphylococci.

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