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Pathogenicity and Medical Microbiology |
Department of Infectious Diseases, Imperial College School of Medicine, London W12 0NN, UK1
Author for correspondence: Shiranee Sriskandan. Tel: +44 208 383 3135. Fax: +44 208 383 3394. e-mail s.sriskandan{at}ic.ac.uk
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.
Keywords: superantigen, nuclease, mouse model, necrotizing fasciitis
Abbreviations: IL-6, interleukin-6; MF, mitogenic factor; PBMC, peripheral blood mononuclear cells
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