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Mutational analysis of the group A streptococcal operon encoding streptolysin S and its virulence role in invasive infection
Author(s) -
Datta Vivekanand,
Myskowski Sandra M.,
Kwinn Laura A.,
Chiem Daniel N.,
Varki Nissi,
Kansal Rita G.,
Kotb Malak,
Nizet Victor
Publication year - 2005
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2005.04583.x
Subject(s) - biology , streptolysin , operon , microbiology and biotechnology , streptococcus pyogenes , streptococcus , virulence , complementation , mutant , decapentaplegic , gene , genetics , staphylococcus aureus , bacteria , bacterial protein , imaginal disc
Summary The pathogen group A Streptococcus (GAS) produces a wide spectrum of infections including necrotizing fasciitis (NF). Streptolysin S (SLS) produces the hallmark β‐haemolytic phenotype produced by GAS. The nine‐gene GAS locus ( sag A– sag I) resembling a bacteriocin biosynthetic operon is necessary and sufficient for SLS production. Using precise, in‐frame allelic exchange mutagenesis and single‐gene complementation, we show sag A, sag B, sag C, sag D, sag E, sag F and sag G are each individually required for SLS production, and that sag E may further serve an immunity function. Limited site‐directed mutagenesis of specific amino acids in the SagA prepropeptide supports the designation of SLS as a bacteriocin‐like toxin. No significant pleotrophic effects of sag A deletion were observed on M protein, capsule or cysteine protease production. In a murine model of NF, the SLS‐negative M1T1 GAS mutant was markedly diminished in its ability to produce necrotic skin ulcers and spread to the systemic circulation. The SLS toxin impaired phagocytic clearance and promoted epithelial cell cytotoxicity, the latter phenotype being enhanced by the effects of M protein and streptolysin O. We conclude that all genetic components of the sag operon are required for expression of functional SLS, an important virulence factor in the pathogenesis of invasive M1T1 GAS infection.