We conclude that the group A streptococcal hyaluronic acid capsule and M protein, but not the cysteine protease, are critical for the development of tissue necrosis, secondary bacteremia, and lethal infection in a murine model of human necrotizing fasciitis.
We present two cases of invasive infection caused by Streptococcus dysgalactiae subsp. equisimilis, one that showed rapidly developing necrotizing fasciitis in a previously healthy man and one that showed severe cellulitis and septic shock even though the bacterium possessed a mutated emm gene, predicted to encode a truncated M protein.
M protein is the most abundant GAS surface protein, and M1 serotype GAS strains are associated with invasive infections, including necrotizing fasciitis and toxic shock syndrome.