Streptococcal infections
Introduction.
Streptococci are part of the normal human microbiota and occur in a variety
of serotypes. Some of these are clearly pathogenic, while others are
opportunistic. Depending on the virulence factros presnt and the serotype, Strep
infections can range from Strep throat to toxic shock syndrome.
Group A Streptococcus: S. pyogenes
- beta hemolysis and bacitracin-sensitive on blood agar
Pharyngitis (Strep throat)
- Sore throat, fever, malaise, headache
- Easily confused with viral causes
Scarlet fever
- Complication of pharyngitis due to lysogenic bacteriophage
- Diffuse red rash except palms, soles & around mouth; strawberry tongue
- Pyrogenic exotoxin produces the rash
Pyoderma (impetigo)
- Pus-filled vesicles; little systemic involvement
Erysipelas
- Local inflammation and systemic signs (fever, chills)
- Outer skin layers very red and raised
Cellulitis
- Deeper skin layers infected
- Redness, less distinct rash, systemic signs
Necrotizing fasciitis
- Deep tissue involvement;
bacteria multiply in muscle and fat
- Tissue necrosis common; rapid spread must be stopped with tissue
debridement
- Systemic signs, shock and death (50% mortailty)
Toxic Shock Syndrome
- Inflammation at site of infection
- Systemic bacteremia, fever, chills, nausea, malaise
- Often associated with NF
- Mortality common due to shock
Rheumatic fever
- Inflammation of heart, blood vessels, joints
- Often associated with strep throat
Acute glomerulonephritis
- Inflammation of kidneys: edema, hypertension, blood & protein in urine
Group B Streptococcus: S. agalacticae
- beta-hemolytic and positive for the CAMP test
- Puerperal fever: sepsis
- Neonatal disease
Viridans Streptococci
- alpha hemolytic; fastidious; many species
- Dental caries (S. mutans)
- Endocarditis
S. pneumoniae
- alpha hemolysis; sensitive to optochin
- Gram-positive diplococci with capsule
- Produce virulence factors: adhesins, IgA protease, pneumolysins (damage
ciliated epithelial cells)
- Cause inflammation at site of infection leading to edema
- Complications include bacteremia and pneumococcal meningitis