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Microbiology > Exam #5: Bacterial Infections of the GI Tract III > Flashcards

Exam #5: Bacterial Infections of the GI Tract III Flashcards

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Biology 101 flashcards
1
Q

List the characteristics of Vibrio cholerae.

A 
Gram negative "comma-shaped" 
Grows in alkaline media
Facultative anaerobe 
Flagellated 
Free-living in water 
Wide temperature range for growth
Require NaCl for growth 
Susceptible to stomach acid; thus, require a high infectious dose
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2
Q

What diseases does Vibrio cholerae cause?

A

Gastroenteritis
Bacteremia

(Cholera)

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3
Q

What diseases does Vibrio parahaemolyticus cause?

A

Gastroenteritis
Bacteremia
Wound infections

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4
Q

What are the symptoms of Cholera?

A

Wide range of clinical manifestations, from asymptomatic to
severe (lethal) watery diarrhea that can kill within hours
- Abrupt onset
- “rice water stool” (mucous)

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5
Q

What is Vibrio cholerae associated with?

A

Spread through contaminated water

*Remember “broad street pump” London

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6
Q

Does Vibrio cholerae infection lead to long-term immunity? Why or why not?

A

Generally, yes

  • Immunity is O-antigen specific (LPS antigen)
  • IF there is a different strain of O-antigen, then one will NOT be immune
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7
Q

What antigen is associated with Vibrio cholerae?

A

O-antigen (LPS)

  • Specifically, O1 is the cholera toxin producing strain
  • There are been 7x pandemics
  • 1-6 were caused by classic O1
  • Currently we are in #7, “El tor” associated (less severe, but longer carriage time)

Non-O1 do NOT produce cholera toxin

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8
Q

What virulence factors are associated with Vibrio cholerae?

A

1) Toxin co-regulated pilus (TCP, co-regulated with cholera toxin), which mediates Vibrio cholerae adherence in intestinal epithelial cells (& then cholera toxin is produced)
2) Cholera toxin, which is an AB toxin that activates adenylate cyclase & leads to an increase in cAMP/ massive efflux of watery secretions

  • No cell damage
  • Similar to ETEC LT toxin
  • Encoded on prophage
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9
Q

How is Vibrio cholerae infection diagnosed?

A

Culture on differential media

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10
Q

How is Vibrio cholerae infection treated?

A

Rehydration therapy (IV)

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11
Q

What are the symptoms caused by Vibrio parahaemolyticus?

A 
Explosive watery diarrhea
Nausea 
Vomiting 
Abdominal cramps 
Low grade fever
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12
Q

What is the virulence factor associated with Vibrio parahaemolyticus?

A

Kanagawa hemolysin, which induces Cl- secretion & thus, watery diarrhea

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13
Q

What is Vibrio parahaemolyticus associated with?How is Vibrio parahaemolyticus prevented?

A
  • Seafood-associated gastroenteritis (most common is Gulf states in US)
  • Proper cooking of shellfish
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14
Q

How is Vibrio parahaemolyticus treated?

A

Self-limiting

Supportive therapy

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15
Q

What are the characteristics of Yersinia enterocolitica?

A

Gram negative coccobacilli

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16
Q

What is Yersinia enterocolitica associated with?

A

Improperly cooked pork

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17
Q

What are the symptoms of Yersinia enterocolitica infection?

A

Fever
Abdominal cramps
Watery to bloody diarrhea

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18
Q

Describe the mechanism of action of Yersinia enterocolitica infection.

A
  • Binds to & invades M-cells in the terminal ileum (similar to Salmonella)
  • Involves T3SS and injection of Yops (Yersinia outer proteins)
  • Produces a heat-stable enterotoxin
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19
Q

How is Yersinia enterocolitica diagnosed?

A

Stool culture

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20
Q

How is Yersinia enterocolitica treated?

A

Self-limiting

Supportive therapy

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21
Q

What are the organisms associated with the large intestine?

A

C. diff

22
Q

What are the characteristics of Clostridium difficile?

A

Gram-positive rod
Anaerobic Test positive
Non-invasive
Spore-forming

Emerging nosocomial infection

23
Q

What are the symptoms of Clostridium difficile infection?

A

Disease & symptoms vary

  • Asymptomatic
  • CDAD
  • Pseudomembrane colitis
  • Fulminant colitis
  • Toxic megacolon
24
Q

What are the symptoms of CDAD?

A

Clostridium difficile associated diarrhea

  • watery diarrhea
  • fecal leukocytes
  • occult blood sometimes seen
25
Q

What are the symptoms of Pseudomembrane colitis?

A
  • C. diff forms large plaques on intestinal epithelium, limiting water uptake
  • As this grows, toxins can be produced, which leads to fulminant colitis
  • Symptoms:
    profuse watery diarrhea
    fecal luekocyutes
    occult blood sometimes seen
26
Q

What are the symptoms of fulminant colitis?

A

Necrosis of the large intestine from C. diff toxin

  • diarrhea may be severe or diminished
  • surgical consult required; patient may present with acute abdomen
27
Q

What are the major virulence factors of Clostridium difficile?

A

Toxin A
Toxin B

Both cause damage to the mucosa; disruption of the host cell cytoskeleton leads to diarrhea

28
Q

How is Clostridium difficile diagnosed?

A

Toxin detection in stool
Culture NOT helpful

*Note that this is commonly seen in patients that are on broad spectrum antibiotics in the hospital

29
Q

How is Clostridium difficile treated?

A

Oral vancomycin or metronidazole

30
Q

How is Clostridium difficile prevented?

A

Fecal transplant

31
Q

What are the characteristics of EHEC?

A

Enterohemorrhagic E. Coli

32
Q

What is EHEC associated with?

A

Contaminated ground beef & vegetables

33
Q

What disease is caused by EHEC?

A

Hemorrhagic colitis i.e. FRANK bloody diarrhea. Symptoms:

  • NO fever
  • marked abdominal tenderness
34
Q

What sequelae is associated with EHEC?

A

Hemolytic Uremic Syndrome (HUS) that can lead to anemia and renal failure

35
Q

Describe the mechanism of action of EHEC.

A
  • EHEC binds & attaches to enterocytes, causing an attaching & effacing lesion like EPEC
  • Also, produces Shiga-like toxin (verotoxin), which blocks translation by cleaving part of the 60S ribosome, which has the effect of destroying cell/ microvilli
  • Verotoxin can enter blood, causing vascular endothelial damage & increased platelet aggregation
  • Platelet-fibrin thrombi form causing ischemic damage to colon, kidneys, and other tissues, leading to hemorrhagic colitis
  • Also, the kidney is rich in the toxin glycolipid receptor (Gb3)–binding to verotoxin leads Hemolytic uremic syndrome & renal failure

Note that cattle & other ruminants LACK Gb3, which is why they can be a reservoir

36
Q

How is EHEC diagnosed?

A
  • Clinically presumptive: bloody diarrhea WITHOUT fever
  • Culture: MacConkey’s agar (lactose fermentation)
  • PCR (NAAT) to detect Shiga-toxin gene
37
Q

How is EHEC treated?

A

Supportive therapy
Antibiotics are CONTRAINDICATED
- Abx induce damage to the bacterial cell; however, the shiga toxin is encoded on a bacteriophage
- When the bacteriophage detects damage, it lysis the cell and leads to increased release of Shiga-toxin (more HUS)

38
Q

How is EHEC prevented?

A

Properly cooked hamburger (& raw vegetables)

39
Q

What are the characteristics of Shigella?

A 
Gram negative rods
Lactose fermenter
Oxidase negative 
Facultative anaerobe 
Intracellular pathogen
40
Q

What does Shigella cause?

A

Dysentery

41
Q

What is Shigella associated with?

A

Poor sanitary infrastructure
Crowded healthcare systems
Day care centers

42
Q

Describe the species distribution of Shigella.

A

S. soneii= developed countries
S. flexneri= developing countries
S. dysentariae= underdeveloped tropical areas

43
Q

Describe the clinical manifestation of Shigella.

A

S. soneii=

  • fever
  • malaise
  • watery diarrhea

S. flexneri & S. dysentariae=

  • fever
  • malaise
  • watery diarrhea
  • abdominal cramps
  • tensemus (urge to defecate)
  • frequently blood & pus-filled stool

Note that S. dysentarie has the potential to develop HUS

44
Q

Describe the pathogenesis of Shigella.

A
  • Acid resistant
  • Adheres selectively to M-cells & invades macrophages
  • Rapid escape from phagosome
  • Rapid induction of macrophage apoptosis
  • Salmonella- like

Also,

  • Interacts with the baso-lateral face of enterocytes
  • Induces uptake via T3SS
  • Lysis of endocytic vacuole
  • Spread by actin polymerization at a pole
  • Listernia monocytogenes-like
45
Q

How is Shigella diagnosed?

A
  • Stool culture using selective media

- Serological tests to confirm species

46
Q

How is Shigella treated?

A

Rehydration therapy

Antibiotic treatment

47
Q

What are the characteristics of EIEC?

A
  • Very uncommon
48
Q

What is the mechanism of action of EIEC?

A

Same as Shigella with NO Shiga-toxin

49
Q

Why is EIEC mechanistically related to Shigella?

A

Appears E. coli obtained pathogenicity island from Shigella via horizontal gene transfer

50
Q

What is an additional consideration of the fecal-oral route aside from food & fingers?

A

Anal sex–>mouth

Microbiology (49 decks)

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