1. Influence of “Level” of Intestinal Invasion

No cell invasion - bind intestinal epithelium but do not enter cells
1. Often produces watery diarrhea without fever
2. E. coli and Vibrio cholera
Localized cell invasion - penetrate intestinal epithelium
1. Can lead to bloody stools
2. Enteroinvasive E. coli, Shigella sp., and Salmonella enteriditis
Invasion of lymph nodes and blood stream
1. Associated with fever, headache, and diarrhea with possible bacteremia and sepsis
2. Salmonella typhi, Yersinia enterocolitica, and Campylobacter jejuni

2. Other Disease Caused by Enteric Organisms

UTIs caused by nosocomial gram negatives
Systemic diseases without diarrhea
1. Meningitis: E. coli K1 in neonates
2. S. typhi, S. paratyphi, and Y. enterocolitica are not necessarily associated with diarrheal infections

3. E. coli

Acquire extrachromosomal DNA containing virulence factors enabling E. coli to cause disease
1. Virulence factors that cause disease: mucosal adherence with pili, ability to invade intestinal epithelia, exotoxin production, endotoxin, iron-binding siderophore
Can cause diarrhea, UTIs, neonatal meningitis, and gram-negative sepsis
Enterotoxigenic E. coli (ETEC)
1. Traveler’s diarrhea
2. Pili enable binding to intestinal epithelium
3. Heat labile toxin (LT) similar to cholera toxin
4. Heat stable toxin (ST)
5. Inhibit sodium, chloride, and bicarbonate resorption in intestines causing water and electrolyte loss
Enterohemorrhagic E. coli (EHEC)
1. Pili plus injected toxins that cause misregulation of epithelial cells
2. Shiga-like toxin (verotoxin) inhibits 60S ribosome
3. Most notable strain O157:H7
4. Encounter: undercooked meat, apple cider, vegetables contaminated with feces
5. Entry: colonize large intestine (bloody diarrhea think colon)
6. Multiplication: directly attach to intestinal epithelium and attach to site of loss of microvilli (attaching and effacing lesion)
7. Spread: systemic damage from local colonization
8. Damage: watery and bloody diarrhea
  1. Hemolytic Uremic Syndrome (HUS): anemia, thrombocytopenia, and renal failure from certain strains such as O157:H7
9. Virulence Factors
  1. Intimin: bacterial adhesion
  2. Tir: initimin receptor that EHEC injects into epithelial cell and focuses actin rearrangements
  3. Shiga-like toxin: responsible for HUS
Enteroinvasive E. coli (EIEC)
1. Virulence factors encoded on plasmid shared by Shigella enabling entry into epithelial cells
2. Produces small amounts Shiga-like toxin
3. Phagocytes invade intestine wall leading to bloody diarrhea with WBC
E. coli and UTIs
1. Pili adapted to urinary tract
2. Dysuria, polyuria, and feeling of full bladder
E. coli Meningitis
1. Neonatal meningitis
E. coli Sepsis
1. Septic shock due to lipid A component of LPS usually the cause of death
E. coli Pneumonia
1. Hospital-acquired pneumonia

4. Klebsiella Pneumonia

Hospitalized patients and alcoholics prone to this disease
Bloody sputum that looks like red jelly
Violent cough that destorys lung tissue

5. Shigella

Non-motile
Humans are the only host
Preschool age children and elderly in nursing homes
Fecal-oral route through hand-to-hand contact
Not part of normal intestinal flora
Bloody diarrhea without systemic symptoms
Indistinguishable from EIEC
Four strains: S. dysenteriae, S. flexneri, S. boydii, S. sonnei
Treat with fluoroquinolones or Bactrim

6. Salmonella

Three strains: S. typhi (carried only by humans), S. cholerae-suis, S. enteriditis
1. S. cholerae-suis patients often have sickle cell anemia and present with osteomyelitis and spleen dysfunction
Not part of normal intestinal flora
S. typhi
1. Encounter: undercooked meat and eggs
2. Entry: colonize small intestine
3. Multiplication: growth in subepithelial layers and in phagocytes
4. Spread: often localized by can infect the gallbladder
5. Damage: watery diarrhea
Typhoid Fever
1. If M cells in small intestine are invaded leading to systemic spread a. drains back into the gut from the gallbladder
2. Fever, headache, abdominal pain in right lower quadrant
3. Treat with ciprofloxacin or ceftriaxone
Carrier State
1. Harbor in gallbladder after infection with typhoid fever
2. Not infected and have no symptoms, but can spread disease
3. Can require surgical removal of gallbladder

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