Streptococcus pyogenes (Group A Strep)

Gram-positive cocci in CHAINS (strepto-), catalase-negative.

🔗 a CHAIN of purple orbs = gram-positive strepto (never a grape cluster)

Lancefield GROUP A carbohydrate antigen (basis of the rapid strep antigen test).

🔗 a war-shield stamped 'A' = Lancefield Group A

Catalase-NEGATIVE (no bubbling with H2O2) — separates Strep from catalase-positive Staph.

🔗 a flat flask with a crossed-out bubble = catalase NEGATIVE (no bubbles)

β-HEMOLYTIC: complete clearing of RBCs on blood agar (driven by streptolysin O).

🔗 flame clearing blood into a transparent beta-shaped ring = complete (beta) hemolysis

BACITRACIN-SENSITIVE (zone of inhibition around the A disc) — distinguishes Group A from bacitracin-RESISTANT Group B.

🔗 the demon RECOILING from the 'A' disc = bacitracin-SENSITIVE (Group A); a bug that shrugs it off = resistant (Group B)

PYR-POSITIVE (pyrrolidonyl arylamidase; rapid test flares bright red).

🔗 a blazing red PYRE turning the strip red = PYR-positive (PYR ~ pyre, turns red)

Hyaluronic acid capsule — antiphagocytic and non-immunogenic (chemically identical to host 'self').

🔗 a see-through 'self' cloak that arrows pass through = non-immunogenic, antiphagocytic capsule

M PROTEIN: antiphagocytic (blocks C3b) AND molecular mimicry of cardiac myosin → rheumatic carditis (type II HS); mitre → mitral valve.

🔗 a literal 'M' on a MITRE helmet = M protein; mitre -> MITRAL valve (molecular mimicry); mirror armor = antiphagocytic

Streptolysin O lyses RBCs (drives β-hemolysis), O2-labile; the ASO titer (with anti-DNase B) marks recent infection.

🔗 an 'O' blade lysing red cells, sealed airtight (O2-labile) = streptolysin O; antibody tongs on it = ASO titer

DNase B degrades host DNA (thins pus, spreads); anti-DNase B titer marks recent infection, especially after SKIN infection.

🔗 scissors marked 'B' cutting a DNA helix = DNase B; the 'B' = anti-DNase B titer

Streptokinase activates plasminogen → plasmin (fibrinolysis, lets the bug spread; used clinically as a thrombolytic).

🔗 a KEY melting a clot = streptoKINASE (key) activates plasminogen -> fibrinolysis

C5a peptidase cleaves the C5a chemoattractant → impairs neutrophil chemotaxis.

🔗 scissors cutting the 'C5a' flare = C5a peptidase cleaving C5a so neutrophils aren't summoned

Hyaluronidase (spreading factor) degrades hyaluronic acid in connective tissue → rapid spread through tissue planes.

🔗 a claw dissolving the wall to spread = hyaluronidase spreading factor degrading tissue planes

Erythrogenic exotoxin A (SpeA) = SUPERANTIGEN (cross-links MHC-II ↔ TCR outside the groove) → scarlet fever.

🔗 a shard reddening a WHOLE crowd at once = superantigen (mass T-cell activation) -> scarlet fever

Streptococcal toxic shock syndrome (STSS): superantigen cytokine storm → fever, rash, shock; classic clue is a PAINFUL skin infection.

🔗 the crowd collapsing into shock from the same superantigen shard = toxic shock

Exotoxin B (SpeB) protease → necrotizing fasciitis ('flesh-eating'): pain out of proportion, dishwater-gray exudate.

🔗 a biting 'B' shard eating flesh to bone = SpeB protease = necrotizing fasciitis

Pharyngitis (#1 bacterial: exudative tonsils, tender ANTERIOR cervical nodes, NO cough). Scarlet fever: sandpaper rash SPARING palms/soles, strawberry tongue, circumoral pallor.

🔗 first flame = throat (pharyngitis); strawberry tongue + sandpaper rash + circumoral pallor sparing palms/soles = scarlet fever

Impetigo (honey-crusted), erysipelas (raised, sharply demarcated), cellulitis.

🔗 honey-crusted blister = impetigo; raised sharply-demarcated red = erysipelas/cellulitis

Acute rheumatic fever — ONLY after pharyngitis, 2–3 wks, type II HS. J♡NES: Joints (migratory), ♡ Carditis (mitral), Nodules (subcutaneous), Erythema marginatum, Sydenham chorea.

🔗 J-heart-N-E-S spelled on the heart (heart replaces the O) = rheumatic fever criteria; reached only by the throat flame

PSGN — after throat OR skin, 1–3 wks. Type III HS, immune complexes, LOW C3, cola-colored urine, periorbital edema, HTN, subepithelial 'humps'.

🔗 kidney dripping cola + tangled glomerular knot + empty 'C3' jar = PSGN with low C3; fed by BOTH throat and skin

Penicillin — NO resistance ever; early treatment PREVENTS rheumatic fever but NOT PSGN.

🔗 a 'PEN' sword that snuffs throat+heart fire but can't reach the kidney = penicillin prevents rheumatic fever, not PSGN