β-hemolytic Streptococcus pyogenes

Where is S. pyogenes found?

Throat, nasopharynx, occasionally skin

C-carbohydrates

Virulence factor of S. pyogenes

protect against lysozyme

Fimbrirae

Virulence factor of S. pyogenes

Adherence

M-protein

Virulence factor of S. pyogenes

Contributes to resistance to phagocytosis

Hyaluronic Acid Capsule

Virulence factor of S. pyogenes

Provokes no immune response

C5a Protease

Virulence factor of S. pyogenes

hinders complement & neutrophil response

Streptolysins

Virulence factor of S. pyogenes

Extracellular toxin

hymolysins; streptolysin O (SLO) and streptolysin S (SLS)- both cause cell & tissue injury

Erythrogenic toxin (pyrogenic)

Virulence factor of S. pyogenes

Extracellular toxin

induces fever & typical red rash

Superantigens

Virulence factor of S. pyogenes

Extracellular toxin

Strong monocyte/lymphocyte stimulants; cause the release of tissue necrotic factor

S. pyogenes Epidemiology & Pathogenesis

Humans only reservoir

Inapparent carriers

Transmission – contact, droplets, food, fomites

Portal of entry generally skin or pharynx

Children predominant group affected for cutaneous and throat infections

Systemic infections and progressive sequelae possible if untreated

Impetigo (pyoderma)

Skin infection of S. pyogenes

superficial lesions that break and form highly contagious crust; often occurs in epidemics in school children; also associated with insect bites, poor hygiene, and crowded living conditions

Erysipelas

Skin infection of S. pyogenes

pathogen enters through a break in the skin and eventually spreads to the dermis and subcutaneous tissues; can remain superficial or become systemic; more invasive

Cellulitis

Skin infection of S. pyogenes

Deeper, boarders less well defined

Necrotizing fasciitis

aka “Flesh-eating bacteria”

most common S. pyogenes

Rare strains make special enzymes and toxins (e.g. superantigens)

Not usually antibiotic resistant

Early diagnosis & treatment important

• 20% mortality

Streptococcal pharyngitis

Throat infection

strep throat

Scarlet fever

Systemic infection

strain of S. pyogenes carrying a prophage that codes for erythrogenic toxin; can lead to sequelae

Septicemia

Systemic infection

Pneumonia

Systemic infection

Streptococcal toxic shock syndrome

Systemic infection

Rheumatic Fever

Long-term complication of Group A infection

follows overt or subclinical pharyngitis in children; Breakdown of tolerance, carditis with extensive valve damage possible, arthritis, chorea, fever

Acute glomerulonephritis

Long-term complication of Group A infection

nephritis, due to immune complexes, increased blood pressure, occasionally heart failure; can become chronic leading to kidney failure