%0 Journal Article %A Sriskandan, Shiranee %A Unnikrishnan, Meera %A Krausz, Thomas %A Cohen, Jonathan %T Mitogenic factor (MF) is the major DNase of serotype M89 Streptococcus pyogenes %D 2000 %J Microbiology, %V 146 %N 11 %P 2785-2792 %@ 1465-2080 %R https://doi.org/10.1099/00221287-146-11-2785 %K nuclease %K IL-6, interleukin-6 %K necrotizing fasciitis %K superantigen %K mouse model %K MF, mitogenic factor %K PBMC, peripheral blood mononuclear cells %I Microbiology Society, %X 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. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-146-11-2785