Mitogenic Factor (MF) Is the Major DNase of Serotype M89 Streptococcus Pyogenes

Microbiology. 2000 Nov;146 ( Pt 11):2785-2792. doi: 10.1099/00221287-146-11-2785.


To investigate the role of mitogenic factor (MF) in streptococcal pathogenesis, the structural gene (mf) encoding this protein was disrupted in a clinical isolate of Streptococcus pyogenes H293, to yield the isogenic mutant H363. Growth in enriched broth and on blood agar was unaffected by disruption of mf. Cell-free broth supernatants from H293 and H363 demonstrated identical promitogenic activities when co-incubated with human peripheral blood mononuclear cells, even when diluted 100000-fold, showing that MF is not a major streptococcal mitogen compared with other secreted superantigens. Disruption of mf resulted in complete loss of DNase B production and detectable DNase activity in H363 compared with the parent strain, confirming that the single gene mf, which is present in all group A streptococcal M serotypes studied, encodes DNase B. Despite loss of DNase activity, the virulence of S. pyogenes in a mouse model of necrotizing fasciitis and myositis was unaffected.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / physiology*
  • Base Sequence
  • DNA Primers / genetics
  • Deoxyribonucleases / genetics*
  • Deoxyribonucleases / physiology*
  • Fasciitis, Necrotizing / etiology
  • Gene Deletion
  • Genes, Bacterial
  • Humans
  • In Vitro Techniques
  • Interleukin-6 / blood
  • Male
  • Mice
  • Mitogens / genetics*
  • Mitogens / physiology*
  • Myositis / etiology
  • Plasmids / genetics
  • Serotyping
  • Streptococcal Infections / etiology
  • Streptococcal Infections / immunology
  • Streptococcal Infections / pathology
  • Streptococcus pyogenes / classification
  • Streptococcus pyogenes / genetics*
  • Streptococcus pyogenes / physiology*
  • Transformation, Genetic
  • Virulence / genetics
  • Virulence / physiology


  • Bacterial Proteins
  • DNA Primers
  • Interleukin-6
  • Mitogens
  • mitogenic factor, Streptococcus
  • Deoxyribonucleases
  • deoxyribonuclease B