Streptococci Flashcards
Strep morphology
Gram+ but in pairs or chains
Beta hemolysis
Completely hemolyse RBC
Alpha hemolysis
Partial hemolysis but looks cloudy, greenish around them
Gamma hemolysis
No hemolysis!
Group A
aka S pyogenes. Hides it’s F protein (binding) and M protein in a capsule, so it has to turn it off in order to bind. Spreading enzymes: hyaluronidase, DNases. Toxins: Strep pyrogenic exotoxin SPE, streptolysin O & S
M protein
inhibits alternate complement pathway, antiphagocytic. Major virulence factor for S pyogenes
Impetigo
Can be caused by strep and staph! Do test (hemolytic, morphology). Polysporin covers both.
Erysipelas
More invasive, more deep than impetigo. Well demarcated edge to red area. Indicative of group A strep. Cellulitis less defined.
Necrotizing fasciitis
Caused by S pyogenes. LTA and F protein bind fibronectin. Less defined edge to area. Delocalized pain from the red site visible, disproportionate amount of pain (burrows into fascia). Sometimes blisters on surface. Hyaluronidase and DNases aid spread quickly. Often associated with toxic shock.
Cellulitis vs necrotizing fasciitis?
Depends on the bug and on your luck (immune system). If it remains localized it will be cellulitis. Can be caused by the same bug sometimes.
Treatment of necrotizing fasciitis
Surgery, lots of antibiotics (penicillin and clindamycin), IgG to mop up M protein
Strep throat vs a cold
Cold has runny nose typically
Strep throat
Swollen uvula, red pinpoint lesions on palate, sometimes white spots on tonsils. But you can’t tell without a culture! Could still be viral.
Scarlet fever
Can be secondary to strep infection. Sand paper rash and strawberry tongue. Results from the toxins (SPE). Treat to avoid acute rheumatic fever
Actue rheumatic fever
Likely cross reactive T cells vs AB that react against self-antigens. Signs: arthritis, carditis, rash, subcutaneous nodules, chorea (involuntary movements like snake??). Can scar heart tissue. Treat strep throat within 7-10 days to avoid it.
