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Updated: May 27, 2026
Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Characterization of SCCmec elements in methicillin-resistant Staphylococcus epidermidis isolated from blood cultures
Karolina Svensson1, Bengt Hellmark, Bo Söderquist
1Department of Laboratory Medicine, Clinical Microbiology, Örebro University Hospital, Örebro, Sweden.
Abstract:
Staphylococcus epidermidis is a major cause of nosocomial infections in immunocompromised patients and the predominant pathogen in catheter-related infections and bloodstream infections. Approximately 70-80% of S. epidermidis carry the mecA gene encoding methicillin resistance. The mecA gene is located on a mobile genetic element, the staphylococcal cassette chromosome mec (SCCmec). The aim of this study was to characterize the SCCmec elements as well as the adjacent arginine catabolic mobile element (ACME) in 30 clinical blood isolates of mecA positive S. epidermidis obtained from neonates and collected over a period of three decades. The ccr and mec gene complexes were identified using PCR. The SCCmec elements were found among 29/30 isolates and 13 different combinations of ccr gene complexes and mec gene complexes were identified. Staphylococcus epidermidis regularly carried multiple copies of ccr gene complexes, but only one class of mec gene complex. Three isolates could be assigned the SCCmec type III (3A). The combinations of ccr gene complexes and the mec gene complexes differed among the three decades. The most frequent combination was class B mec in combination with ccr1 and ccr2. Staphylococcus epidermidis may constitute a large reservoir for SCCmec elements, and frequent exchange of mobile genetic elements between staphylococcal species may explain the emergence of new MRSA strains.
Insights
Staphylococcus epidermidis, a common cause of hospital infections, frequently carries methicillin resistance genes on mobile elements. Characterizing these elements reveals diverse combinations, highlighting their role in emerging MRSA strains.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Staphylococcus epidermidis is a significant cause of nosocomial infections, particularly in immunocompromised individuals.
- Methicillin resistance, mediated by the mecA gene located on staphylococcal cassette chromosome mec (SCCmec) elements, is prevalent in S. epidermidis.
- Understanding SCCmec diversity is crucial for tracking the evolution of antibiotic resistance.
Purpose of the Study:
- To characterize SCCmec elements and adjacent arginine catabolic mobile elements (ACME) in clinical S. epidermidis blood isolates.
- To investigate the diversity and evolution of SCCmec elements over three decades in neonatal isolates.
- To identify combinations of ccr and mec gene complexes within these isolates.
Main Methods:
- Polymerase Chain Reaction (PCR) was used to identify ccr and mec gene complexes.
- Analysis of 30 clinical blood isolates of mecA-positive S. epidermidis collected over 30 years.
- Characterization of SCCmec and ACME elements.
Main Results:
- SCCmec elements were identified in 29 out of 30 isolates.
- Thirteen distinct combinations of ccr and mec gene complexes were observed.
- A frequent combination involved class B mec with ccr1 and ccr2; SCCmec type III (3A) was found in three isolates.
- Combinations of SCCmec elements varied across the three decades studied.
Conclusions:
- Staphylococcus epidermidis acts as a reservoir for diverse SCCmec elements.
- Frequent exchange of mobile genetic elements among staphylococcal species likely contributes to the emergence of new Methicillin-Resistant Staphylococcus aureus (MRSA) strains.
- The characterized SCCmec elements provide insights into the genetic plasticity driving antibiotic resistance in S. epidermidis.
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