Virulence Factors and Toxins

Question 1

Protein A

Answer 1

Binds Fc region of IgG
Prevents opsonization and phagocytosis
Expressed by s. aureus

Question 2

IgA protease

Answer 2

Cleaves IgA
Secreted by S.pneumo, H. influenza B, Neisseria
Colonize respiratory mucosa

Question 3

M protein

Answer 3

Helps prevent phagocytosis
Expressed by group A strep
Rheumatic fever

Question 4

Type III secretion system

Answer 4

aka injectisome
Needle-like protein appendage facilitating direct delivery of toxins from certain gram- bacteria to host cell
Pseudomonas, salmonella, shigella, e.coli

Question 5

Diptheria toxin

Answer 5

Corynebacterium diphtheriae
Inactivate EF2
Pharyngitis with pseudomembranes in throat and severe lymphadenopathy (bull neck)

Question 6

Exotoxin A

Answer 6

Pseudomonas aeruginosa
Inactivate EF2
Host cell death

Question 7

Shiga toxin

Answer 7

Shigella
Inactivate 60S ribosome by removing adenine from rRNA
GI mucosal damage -> dysentery; ST also enhances cytokine release, causing hemolytic uremic syndrome

Question 8

Shiga-like toxin

Answer 8

Enterohemorrhagic E. coli (EHEC)
Inactivate 60S ribosome by removing adenine from rRNA
SLT enhances cytokine release, causing HUS (prototypically in EHEC serotype O157:H7). Unlike shigella, EHEC does not invade host ells

Question 9

Heat labile toxin

Answer 9

Enterotoxigenic E.coli (ETEC)
OVeractivates adenylate cyclase (increases cAMP) -> inc Cl secretion in gut and H2O efflux

Watery diarrhea

Question 10

Heat stable toxin

Answer 10

Overactivates guanylate cyclase (inc cGMP) -> dec resportion of NaCl and H2) in gut

Watery diarrhea

Question 11

Edema toxin

Answer 11

Bacillus anthracis
Mimics adenylate cyclase enzyme (inc cGMP)

Likely responsible for characteristic edematous borders of black eschar in cutaneous anthrax

Question 12

Cholera toxin

Answer 12

Vibrio cholerae
Overactivates adenylate cyclase (inc cAMP) by permanently activating G2 -> Cl secretion in gut and H2O efflux
Voluminous “rice-water” diarrhea

Question 13

Pertussis toxin

Answer 13

Bordetella pertussis

Overactivates adenylate cyclase (inc cAMP) by disabling Gi, impairing phagocytosis to permit survival of microbe

Question 14

Tetanospasmin

Answer 14

Clostridium tetani
Protease that cleaves SNARE protein required for NT release via vesicular fusion

Spasticity, risus sardonicus, “lockjaw”, prevents release of inhibitory GABA and glycine from Renshaw cells in spinal cord

Question 15

Botulinum toxin

Answer 15

Clostridium botulinum
Protease that cleaves SNARE protein required for NT release via vesicular fusion

Flaccid paralysis, floppy baby; toxin prevents release of stimulatory ACh signals at neuromuscular junctions -> flaccid paralysis

Question 16

Alpha toxin

Answer 16

Clostridium perfringens
Phospholipase (lecithinase) that degrades tissue and cell membranes
Degradation of phospholipids -> myonecrosis (Gas gangrene) and hemolysis (double zone of hemolysis on blood agar)

Question 17

Streptolysin O

Answer 17

Streptococcus pyogenes
Protein that degrades cell membrane
Lyses RBCs; contributes to B-hemolsis; host antibodies against toxin (ASO) used to diagnose rheumatic fever (do not confuse with immune complexes of poststreptococcal glomerulonephritis)

Question 18

Toxic shock syndrome toxin (TSST-1)

Answer 18

Binds to MHCII and TCR outside of antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-gamma, and TNF-alpha which leads to shock
TSS: fever, rash, shock; other toxins cause scalded skin syndrome (exfoliative toxin) and food posoning (enterotoxin)

Question 19

Exotoxin A (streptococcus pyogenes)

Answer 19

Binds to MHCII and TCR outside of antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-gamma, and TNF-alpha -> shock

TSS: fever, rash shock