S pyogenes tends to colonize the upper respiratory tract and is highly virulent as it overcomes the host defense system. The most common forms of S pyogenes disease include respiratory and skin infections, with different strains usually responsible for each form.
The cell wall of S pyogenes is very complex and chemically diverse. The antigenic components of the cell are the virulence factors. The extracellular components responsible for the disease process include invasins and exotoxins. The outermost capsule is composed of hyaluronic acid, which has a chemical structure resembling host connective tissue, allowing the bacterium to escape recognition by the host as an offending agent. Thus, the bacterium escapes phagocytosis by neutrophils or macrophages, allowing it to colonize. Lipoteichoic acid and M proteins located on the cell membrane traverse through the cell wall and project outside the capsule.
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Invasive soft tissue infection due to Streptococcus pyogenes. This child developed fever and soft-tissue swelling on the fifth day of a varicella-zoster infection. Leading edge aspirate of cellulitis grew S pyogenes. Although the patient responded to intravenous penicillin and clindamycin, operative débridement was necessary because of clinical suspicion of early necrotizing fasciitis.
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Streptococcus group A infections. Beta hemolysis is demonstrated on blood agar media.
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Streptococcus group A infections. M protein.
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Streptococcus group A infections. Erysipelas is a group A streptococcal infection of skin and subcutaneous tissue.
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Streptococcus group A infections. White strawberry tongue observed in streptococcal pharyngitis. Image courtesy of J. Bashera.
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Streptococcus group A infections. Streptococcal rash. Image courtesy of J. Bashera.
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Group A Streptococcus on Gram stain of blood isolated from a patient who developed toxic shock syndrome.
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Streptococcus group A infections. Necrotizing fasciitis of the left hand in a patient who had severe pain in the affected area.
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Streptococcus group A infections. Patient who had had necrotizing fasciitis of the left hand and severe pain in the affected area (from Image 8). This photo was taken at a later date, and the wound is healing. The patient required skin grafting.
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Streptococcus group A infections. Gangrenous streptococcal cellulitis in a patient with diabetes.
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Erythema secondary to group A streptococcal cellulitis.
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Invasive soft tissue infection due to Streptococcus pyogenes. This child developed fever and soft-tissue swelling on the fifth day of a varicella-zoster infection. Leading edge aspirate of cellulitis grew S pyogenes. Although the patient responded to intravenous penicillin and clindamycin, operative débridement was necessary because of clinical suspicion of early necrotizing fasciitis.
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Streptococcus group A infections. Necrotizing fasciitis rapidly progresses from erythema to bullae formation and necrosis of skin and subcutaneous tissue.
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Throat swab. Video courtesy of Therese Canares, MD; Marleny Franco, MD; and Jonathan Valente, MD (Rhode Island Hospital, Brown University).
