Roles of 34 virulence genes in the evolution of hospital- and community-associated strains of methicillin-resistant Staphylococcus aureus

J Infect Dis. 2006 Jun 1;193(11):1495-503. doi: 10.1086/503777. Epub 2006 Apr 21.


Background: The extent to which the horizontal transfer of virulence genes has contributed to the emergence of contemporary virulent strains of methicillin-resistant Staphylococcus aureus (MRSA) in hospital and community settings is poorly understood.

Methods: Epidemiologically well-characterized MRSA isolates collected over 8.5 years were genotyped and tested for the presence of 34 virulence genes.

Results: Six strain types accounted for 88.2% of all MRSA infections. The evolution of contemporary hospital and community phenotypes within the CC8 and CC30 lineages--2 background genomes that produced historical pandemic MRSA clones--were associated with multiple horizontal acquisitions of virulence genes. The epidemic community phenotype of a CC8 strain, designated ST8:USA300, was linked to the acquisition of staphylococcal cassette chromosome (SCC)mec type IV, the genes for Panton-Valentine leukocidin (PVL), and the enterotoxin Q and K genes. Similarly, the epidemic community phenotype of a CC30 strain, ST30:USA1100, was linked to the acquisition of SCCmec type IV and the pvl genes. In contrast, the epidemic hospital phenotype of another CC30 strain, ST36:USA200, was associated with the acquisition of SCCmec type II, the enterotoxin A gene, and the toxic shock syndrome toxin 1 gene. The pvl genes appear not to be essential for the evolution OF other community-associated strains of mrsa, including ST8:USA500 and ST59:USA1000.

Conclusions: The horizontal transfer of virulence genes, although infrequent, is epidemiologically associated with the emergence of new virulent strains of MRSA.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Toxins / genetics
  • Community-Acquired Infections / microbiology*
  • Cross Infection / microbiology*
  • DNA Fingerprinting
  • DNA, Bacterial / genetics
  • Electrophoresis, Gel, Pulsed-Field
  • Enterotoxins / genetics
  • Evolution, Molecular*
  • Exotoxins / genetics
  • Gene Transfer, Horizontal
  • Genotype
  • Humans
  • Leukocidins
  • Methicillin Resistance / genetics
  • Polymerase Chain Reaction
  • Polymorphism, Restriction Fragment Length
  • San Francisco
  • Staphylococcal Infections / microbiology*
  • Staphylococcus aureus / classification
  • Staphylococcus aureus / drug effects
  • Staphylococcus aureus / genetics*
  • Staphylococcus aureus / isolation & purification
  • Superantigens / genetics
  • Virulence Factors / genetics*


  • Bacterial Toxins
  • DNA, Bacterial
  • Enterotoxins
  • Exotoxins
  • Leukocidins
  • Panton-Valentine leukocidin
  • Superantigens
  • Virulence Factors
  • enterotoxin F, Staphylococcal