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Mobile genetic element-encoded cytolysin connects virulence to methicillin resistance in MRSA

Shu Y Queck1, Burhan A Khan, Rong Wang

  • 1Laboratory of Human Bacterial Pathogenesis, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD, USA.

Plos Pathogens
|August 4, 2009
PubMed

Insights

A newly discovered gene, psm-mec, on the SCCmec mobile genetic element enhances Staphylococcus aureus virulence. This finding reveals how antibiotic resistance elements can also contribute to bacterial pathogenesis.

Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Molecular Biology

Background:

  • Bacterial virulence and antibiotic resistance significantly impact disease severity and treatment.
  • Mobile genetic elements (MGEs) often carry genes for virulence and antibiotic resistance.
  • In Staphylococcus aureus, MGEs with resistance genes typically lack virulence genes.

Purpose of the Study:

  • To identify and characterize novel virulence factors in Staphylococcus aureus.
  • To investigate the role of MGEs in the co-acquisition of virulence and antibiotic resistance traits.
  • To explore the function of a newly identified psm gene, psm-mec, located on the SCCmec element.

Main Methods:

  • Gene identification and sequencing of the psm-mec gene within the SCCmec element.
  • Analysis of psm-mec expression in various Staphylococcus aureus strains.
  • Assessment of PSM-mec's physico-chemical, pro-inflammatory, and cytolytic properties.
  • In vivo studies to evaluate the impact of psm-mec expression on immune evasion and disease severity.

Main Results:

  • A novel psm gene, psm-mec, was identified within the SCCmec element, a key MGE in Staphylococcus aureus.
  • PSM-mec exhibited strong expression and possessed characteristic PSM properties, including pro-inflammatory and cytolytic activity.
  • Expression of psm-mec significantly influenced immune evasion and disease progression in strains with low endogenous PSM production.
  • Horizontal gene transfer of SCCmec elements carrying psm-mec can contribute to staphylococcal virulence.

Conclusions:

  • The study identifies a previously unknown role for methicillin resistance clusters (SCCmec) in staphylococcal pathogenesis.
  • The psm-mec gene represents a novel virulence factor that can be combined with antibiotic resistance genes on MGEs.
  • Co-localization of virulence and antibiotic resistance determinants on MGEs like SCCmec has significant implications for bacterial evolution and treatment strategies.

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