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Microbiology ` microbiology—basic bacteriology Microbiology ` microbiology—basic bacteriology SEcTioN ii 133
Bacteria with exotoxins (continued)
bacteria toXiN mecHaNism maNiFestatioN
Lyse cell membranes
Clostridium Alpha toxin Phospholipase (lecithinase) Degradation of phospholipids myonecrosis
perfringens that degrades tissue and (“gas gangrene”) and hemolysis (“double zone”
cell membranes of hemolysis on blood agar)
Streptococcus Streptolysin O Protein that degrades cell Lyses RBCs; contributes to β-hemolysis;
pyogenes membrane host antibodies against toxin (ASO) used to
diagnose rheumatic fever (do not confuse
with immune complexes of poststreptococcal
glomerulonephritis)
Superantigens causing shock
Staphylococcus Toxic shock Cross-links β region of Toxic shock syndrome: fever, rash, shock; other
aureus syndrome toxin TCR to MHC class II toxins cause scalded skin syndrome (exfoliative
(TSST-1) on APCs outside of the toxin) and food poisoning (heat-stable
antigen binding site enterotoxin)
Streptococcus Erythrogenic overwhelming release Toxic shock–like syndrome: fever, rash, shock;
pyogenes exotoxin A of IL-1, IL-2, IFN-γ, and scarlet fever
TNF-α shock
Endotoxin LPS found in outer membrane of gram ⊝ ENDOTOXINS:
bacteria (both cocci and rods). Composed of Edema
O antigen + core polysaccharide + lipid A (the Nitric oxide
toxic component). DIC/Death
Released upon cell lysis or by living cells by Outer membrane
blebs detaching from outer surface membrane TNF-α
(vs exotoxin, which is actively secreted). O-antigen + core polysaccharide + lipid A
Three main effects: macrophage activation eXtremely heat stable
(TLR4/CD14), complement activation, and IL-1 and IL-6
tissue factor activation. Neutrophil chemotaxis
Shock
IL-1, IL-6 Fever
Macrophage activation TNF-α Fever and hypotension
(TLR4/CD14)
Nitric oxide Hypotension
Histamine release:
C3a
Endotoxin Hypotension and edema
(lipid A component) Complement activation
C5a Neutrophil chemotaxis
Coagulation
Tissue factor activation DIC
cascade
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