INFECTIOUS DISEASE EXAM 2 [2026] | UPDATED ACTUAL
| Question and Answer | VERIFIED ANSWERS AND
COMPLETE REVIEW
• ETEC - Enterotoxigenic E. coli -✓✓ ANSWER: "Traveler's diarrhea" (developing
countries).
Spread by fecally contaminated food/water.
High infectious dose (no person-to-person spread).
Symptoms: watery diarrhea (no blood), cramps, nausea, vomiting.
Virulence factors:
Heat-labile toxin (LT): ↑cAMP → chloride + water secretion.
Heat-stable toxin (ST): ↑cGMP → fluid secretion.
Colonization factors (fimbriae CFA/I-III) for gut adherence.
• EPEC - Enteropathogenic E. coli -✓✓ ANSWER: Infant diarrhea (developing
world; daycare/nurseries in developed).
Low infectious dose → person-to-person spread.
Symptoms: severe watery diarrhea, vomiting, fever.
Pathology: Attachment and effacement (A/E) → destruction of microvilli.
,Virulence factors:
Bundle-forming pili (BFP) for microcolony formation.
Type III secretion system injects proteins (e.g., Tir → binds bacterial intimin,
disrupts cytoskeleton, cell death).
• EAEC - Enteroaggregative E. coli -✓✓ ANSWER: Chronic watery diarrhea in
infants & travelers. Can stunt growth in children.
Symptoms: persistent diarrhea.
Pathology: "Stacked-brick" adhesion → biofilm formation.
Virulence factors:
Aggregative adherence fimbriae (AAF-1).
Biofilm protects from phagocytosis & antibiotics.
Toxins: enteroaggregative heat-stable toxin + plasmid-encoded toxin.
• EHEC - Enterohemorrhagic E. coli -✓✓ ANSWER: Most common pathogenic
strain in the developed world (O157:H7 classic).
Source: undercooked meat, contaminated water, produce, cattle feces.
Very low infectious dose (person-to-person spread possible).
, Symptoms: bloody diarrhea, abdominal pain, sometimes Hemolytic Uremic
Syndrome (HUS: renal failure, thrombocytopenia, anemia).
Virulence factors:
Shiga toxins (Stx-1, Stx-2) → block protein synthesis.
Attaching/effacing lesions (like EPEC).
• EIEC - Enteroinvasive E. coli -✓✓ ANSWER: Rare (O124, O143, O164).
Symptoms: watery diarrhea → dysentery (bloody diarrhea, fever, cramps).
Pathology: Invade epithelial cells via endocytosis, escape vacuole, multiply in
cytoplasm → cell death + ulceration.
Similar to Shigella.
• O antigen -✓✓ ANSWER: Polysaccharide portion of LPS. Strain-specific.
• K antigen -✓✓ ANSWER: Capsule polysaccharide. Protects against phagocytosis,
complement, antibody binding.
• H antigen -✓✓ ANSWER: Flagellar proteins. Variable between strains.
• Endotoxic shock -✓✓ ANSWER: systemic reaction to LPS → clotting, vascular
leakage, shock, organ failure.
| Question and Answer | VERIFIED ANSWERS AND
COMPLETE REVIEW
• ETEC - Enterotoxigenic E. coli -✓✓ ANSWER: "Traveler's diarrhea" (developing
countries).
Spread by fecally contaminated food/water.
High infectious dose (no person-to-person spread).
Symptoms: watery diarrhea (no blood), cramps, nausea, vomiting.
Virulence factors:
Heat-labile toxin (LT): ↑cAMP → chloride + water secretion.
Heat-stable toxin (ST): ↑cGMP → fluid secretion.
Colonization factors (fimbriae CFA/I-III) for gut adherence.
• EPEC - Enteropathogenic E. coli -✓✓ ANSWER: Infant diarrhea (developing
world; daycare/nurseries in developed).
Low infectious dose → person-to-person spread.
Symptoms: severe watery diarrhea, vomiting, fever.
Pathology: Attachment and effacement (A/E) → destruction of microvilli.
,Virulence factors:
Bundle-forming pili (BFP) for microcolony formation.
Type III secretion system injects proteins (e.g., Tir → binds bacterial intimin,
disrupts cytoskeleton, cell death).
• EAEC - Enteroaggregative E. coli -✓✓ ANSWER: Chronic watery diarrhea in
infants & travelers. Can stunt growth in children.
Symptoms: persistent diarrhea.
Pathology: "Stacked-brick" adhesion → biofilm formation.
Virulence factors:
Aggregative adherence fimbriae (AAF-1).
Biofilm protects from phagocytosis & antibiotics.
Toxins: enteroaggregative heat-stable toxin + plasmid-encoded toxin.
• EHEC - Enterohemorrhagic E. coli -✓✓ ANSWER: Most common pathogenic
strain in the developed world (O157:H7 classic).
Source: undercooked meat, contaminated water, produce, cattle feces.
Very low infectious dose (person-to-person spread possible).
, Symptoms: bloody diarrhea, abdominal pain, sometimes Hemolytic Uremic
Syndrome (HUS: renal failure, thrombocytopenia, anemia).
Virulence factors:
Shiga toxins (Stx-1, Stx-2) → block protein synthesis.
Attaching/effacing lesions (like EPEC).
• EIEC - Enteroinvasive E. coli -✓✓ ANSWER: Rare (O124, O143, O164).
Symptoms: watery diarrhea → dysentery (bloody diarrhea, fever, cramps).
Pathology: Invade epithelial cells via endocytosis, escape vacuole, multiply in
cytoplasm → cell death + ulceration.
Similar to Shigella.
• O antigen -✓✓ ANSWER: Polysaccharide portion of LPS. Strain-specific.
• K antigen -✓✓ ANSWER: Capsule polysaccharide. Protects against phagocytosis,
complement, antibody binding.
• H antigen -✓✓ ANSWER: Flagellar proteins. Variable between strains.
• Endotoxic shock -✓✓ ANSWER: systemic reaction to LPS → clotting, vascular
leakage, shock, organ failure.
