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Updated: Jul 2, 2025
Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Methicillin Resistance Elements in the Canine Pathogen Staphylococcus pseudintermedius and Their Association with the
Gordon Y C Cheung1, Ji Hyun Lee1, Ryan Liu1
1Pathogen Molecular Genetics Section, Laboratory of Bacteriology, National Institute of Allergy and Infectious Diseases (NIAID), US National Institutes of Health (NIH), Bethesda, MD 20892, USA.
Abstract:
Staphylococcus pseudintermedius is a frequent cause of infections in dogs. Infectious isolates of this coagulase-positive staphylococcal species are often methicillin- and multidrug-resistant, which complicates therapy. In staphylococci, methicillin resistance is encoded by determinants found on mobile genetic elements called Staphylococcal Chromosome Cassette mec (SCCmec), which, in addition to methicillin resistance factors, sometimes encode additional genes, such as further resistance factors and, rarely, virulence determinants. In this study, we analyzed SCCmec in a collection of infectious methicillin-resistant S. pseudintermedius (MRSP) isolates from predominant lineages in the United States. We found that several lineages characteristically have specific types of SCCmec elements and Agr types and harbor additional factors in their SCCmec elements that may promote virulence or affect DNA uptake. All isolates had SCCmec-encoded restriction-modification (R-M) systems of types I or II, and sequence types (STs) ST84 and ST64 had one type II and one type I R-M system, although the latter lacked a complete methylation enzyme gene. ST68 isolates also had an SCCmec-encoded CRISPR system. ST71 isolates had a psm-mec gene, which, in all but apparently Agr-dysfunctional isolates, produced a PSM-mec peptide toxin, albeit at relatively small amounts. This study gives detailed insight into the composition of SCCmec elements in infectious isolates of S. pseudintermedius and lays the genetic foundation for further efforts directed at elucidating the contribution of identified accessory SCCmec factors in impacting SCCmec-encoded and thus methicillin resistance-associated virulence and resistance to DNA uptake in this leading canine pathogen.
Insights
Methicillin-resistant Staphylococcus pseudintermedius (MRSP) in dogs harbors specific Staphylococcal Chromosome Cassette mec (SCCmec) elements. These elements contain genes influencing virulence and DNA uptake, impacting canine infections.
Area of Science:
- Veterinary Microbiology
- Bacterial Genetics
- Antimicrobial Resistance
Background:
- Staphylococcus pseudintermedius is a major cause of canine infections.
- Methicillin and multidrug resistance in S. pseudintermedius complicates treatment.
- Staphylococcal Chromosome Cassette mec (SCCmec) elements carry resistance and virulence genes.
Purpose of the Study:
- To analyze the composition of SCCmec elements in infectious methicillin-resistant S. pseudintermedius (MRSP) isolates from the United States.
- To identify specific SCCmec types associated with predominant MRSP lineages.
- To investigate accessory genes within SCCmec that may influence virulence or DNA uptake.
Main Methods:
- Analysis of SCCmec elements in a collection of MRSP isolates.
- Characterization of sequence types (STs) and Agr types.
- Identification of restriction-modification (R-M) systems, CRISPR systems, and psm-mec genes within SCCmec.
Main Results:
- Distinct SCCmec types and Agr types were associated with specific MRSP lineages.
- All isolates possessed SCCmec-encoded R-M systems (types I or II).
- ST71 isolates carried a psm-mec gene encoding a peptide toxin, and ST68 isolates had an SCCmec-encoded CRISPR system.
Conclusions:
- MRSP SCCmec elements are diverse and lineage-specific.
- Accessory SCCmec factors, including R-M systems, CRISPR, and psm-mec, may contribute to MRSP virulence and DNA uptake.
- This genetic insight provides a foundation for understanding MRSP pathogenesis and resistance.
