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

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Flashcards in Exam #5: Bacterial Infections of the GI Tract III Deck (50):
1

List the characteristics of Vibrio cholerae.

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

2

What diseases does Vibrio cholerae cause?

Gastroenteritis
Bacteremia

(Cholera)

3

What diseases does Vibrio parahaemolyticus cause?

Gastroenteritis
Bacteremia
Wound infections

4

What are the symptoms of Cholera?

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

5

What is Vibrio cholerae associated with?

Spread through contaminated water

*Remember "broad street pump" London

6

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

Generally, yes

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

7

What antigen is associated with Vibrio cholerae?

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

8

What virulence factors are associated with Vibrio cholerae?

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

9

How is Vibrio cholerae infection diagnosed?

Culture on differential media

10

How is Vibrio cholerae infection treated?

Rehydration therapy (IV)

11

What are the symptoms caused by Vibrio parahaemolyticus?

Explosive watery diarrhea
Nausea
Vomiting
Abdominal cramps
Low grade fever

12

What is the virulence factor associated with Vibrio parahaemolyticus?

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

13

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

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

14

How is Vibrio parahaemolyticus treated?

Self-limiting
Supportive therapy

15

What are the characteristics of Yersinia enterocolitica?

Gram negative coccobacilli

16

What is Yersinia enterocolitica associated with?

Improperly cooked pork

17

What are the symptoms of Yersinia enterocolitica infection?

Fever
Abdominal cramps
Watery to bloody diarrhea

18

Describe the mechanism of action of Yersinia enterocolitica infection.

- 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

19

How is Yersinia enterocolitica diagnosed?

Stool culture

20

How is Yersinia enterocolitica treated?

Self-limiting
Supportive therapy

21

What are the organisms associated with the large intestine?

C. diff

22

What are the characteristics of Clostridium difficile?

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

Emerging nosocomial infection

23

What are the symptoms of Clostridium difficile infection?

Disease & symptoms vary
- Asymptomatic
- CDAD
- Pseudomembrane colitis
- Fulminant colitis
- Toxic megacolon

24

What are the symptoms of CDAD?

Clostridium difficile associated diarrhea
- watery diarrhea
- fecal leukocytes
- occult blood sometimes seen

25

What are the symptoms of Pseudomembrane colitis?

- 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

What are the symptoms of fulminant colitis?

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

What are the major virulence factors of Clostridium difficile?

Toxin A
Toxin B

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

28

How is Clostridium difficile diagnosed?

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

How is Clostridium difficile treated?

Oral vancomycin or metronidazole

30

How is Clostridium difficile prevented?

Fecal transplant

31

What are the characteristics of EHEC?

Enterohemorrhagic E. Coli

32

What is EHEC associated with?

Contaminated ground beef & vegetables

33

What disease is caused by EHEC?

Hemorrhagic colitis i.e. FRANK bloody diarrhea. Symptoms:
- NO fever
- marked abdominal tenderness

34

What sequelae is associated with EHEC?

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

35

Describe the mechanism of action of EHEC.

- 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

How is EHEC diagnosed?

- Clinically presumptive: bloody diarrhea WITHOUT fever
- Culture: MacConkey's agar (lactose fermentation)
- PCR (NAAT) to detect Shiga-toxin gene

37

How is EHEC treated?

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

How is EHEC prevented?

Properly cooked hamburger (& raw vegetables)

39

What are the characteristics of Shigella?

Gram negative rods
Lactose fermenter
Oxidase negative
Facultative anaerobe
Intracellular pathogen

40

What does Shigella cause?

Dysentery

41

What is Shigella associated with?

Poor sanitary infrastructure
Crowded healthcare systems
Day care centers

42

Describe the species distribution of Shigella.

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

43

Describe the clinical manifestation of Shigella.

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

Describe the pathogenesis of Shigella.

- 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

How is Shigella diagnosed?

- Stool culture using selective media
- Serological tests to confirm species

46

How is Shigella treated?

Rehydration therapy
Antibiotic treatment

47

What are the characteristics of EIEC?

- Very uncommon

48

What is the mechanism of action of EIEC?

Same as Shigella with NO Shiga-toxin

49

Why is EIEC mechanistically related to Shigella?

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

50

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

Anal sex-->mouth

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