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

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

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1
Q

What does MacConkey agar test? What does a positive test look like & what bacteria are associated with it? What does a negative test look like, and what bacteria are associated with it?

A

MacConkey agar= lactose fermentation

Positive= red colonies/ agar
- E. coli

Negative= white colonies/ agar
- Salmonella, Shigella

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2
Q

What is the Indole test? What does a positive test look like & what bacteria are associated with it? What does a negative test look like, and what bacteria are associated with it?

A

A test for indole production

Positive= red

  • E. coli
  • Virbri

Negative= white
- Salmonella

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3
Q

What does a positive Hydrogen Sulfite (H2S) production test look like ? What is it indicative of?

A

A positive test shows as a black precipitate. It is used to differentiate between Salmonella & Shigella.

  • Salmonella= black (producer)
  • Shigella= white (non-producer)
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4
Q

List the different virotypes of pathogenic E. Coli & their acronyms.

A

Enterotoxigenic (ETEC)
Enteropathogenic (EPEC)
Enterohemorrhagic (EHEC)
Enteroinvasive (EtEC)

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5
Q

Describe the characteristics of EPEC.

A 
Gram (-) rod 
Lactose fermenter
Fast Lactose fermenter
Facultative anaerobe 
Moderately invasive
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6
Q

What is EPEC associated with?

A

Pediatric diarrhea

*Note that specifically, EPEC is associated with pediatric watery diarrhea, which is caused by tissue destruction.

Think P for Peds

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7
Q

Describe the mechanism of action of EPEC.

A

1) BfpA (bundle forming pilus) binds the the intestinal epithelium
2) Type III Secretion System

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8
Q

What are the clinical manifestations of EPEC?

A

Watery diarrhea without toxins

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9
Q

What are the morphological characteristics of EPEC?

A

Attaching & effacing

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10
Q

How is EPEC diagnosed?

A

Culture & biochemical tests

  • Ferments lactose, thus it is red on MacConkey agar
  • Indole positive i.e. red on indole test

PCR

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11
Q

What is the treatment for EPEC?

A

Supportive therapy

Antibiotics can reduce the length of disease, but not routinely used

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12
Q

What are the characteristics of ETEC?

A 
Gram negative rod 
Lactose fermenter 
Fast lactose fermenter 
Faculative anaerobe
NOT invasive
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13
Q

What is ETEC assocaited with?

A

“Traveler’s diarrhea”

Associated with travel to developing countries and consumption of contaminated water or ice (produces a watery diarrhea)

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14
Q

Describe the mechanism of action of ETEC.

A

1) Fimbraie adhere to the epithelial cell wall
2) Toxins are produced:
- LT
- ST

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15
Q

What is the difference between LT & ST toxins?

A

LT= AB toxin that increases adenylate cyclase & cAMP, increasing the production of solutes that produce osmotic effect–>diarrhea

ST= Non- AB toxin that increases cGMP and solute movement that osmotically produces watery diarrhea

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16
Q

How is ETEC diagnosed?

A
  • Clinically

- DNA probes to detect LT & ST

17
Q

How is ETEC treated?

A

Supportive therapy

18
Q

Describe the characteristics of Salmonella Typhi.

A 
Gram negative rod 
Lactose non-fermenter
Oxidase negative 
Facultative anaerobe 
Motile 
Flagellated (+ H-antigen)
Acid tolerant
19
Q

How is Salmonella typhi transmitted?

A

Human to human

Fecal to oral

20
Q

What are the clinical manifestations of Salmonella typhi?

A
  • Fever with headache
  • Rising fever over 3 days
  • Thyphoid fever
  • GI symptoms

Note that there is a 13 day incubation period

21
Q

Describe the mechanism of action of Salmonella typhi.

A

1) Adherence to M-cells (antigen presenting cells to the Peyer’s patch in the ileum) & enterocytes
2) Type III secretion system, secretes SSPs into the cell that causes membrane ruffling & escape from the vacuole
3) Escape from the cytosol
4) Can then travel to the lymph or bloodstream, causing bacteremia/ spesis

22
Q

How is Salmonella typhi diagnosed?

A

Culture of stool and blood samples on selective media

23
Q

How is Salmonella typhi treated?

A

Antibiotic therapy based on susceptibility profile

24
Q

How is Salmonella typhi prevented?

A

Avoid potential sources of infection

  • Drink bottled water (no ice)
  • Eat thoroughly cooked food
  • Avoid raw fruits & vegetables

Vaccination for travelers to endemic areas

25
Q

Describe the characteristics of Small Intestine Nontyphoidal Salmonella.

A 
Gram negative rod 
Lactose non-fermenter 
Oxidase negative 
Facultative anaerobe 
Motile 
Flagellated (+ H-antigen)
Acid tolerant

Note that this is exactly the same as S. typhi, the only difference is that this one is not as well adapted to humans

26
Q

What is Small Intestine Nontyphoidal Salmonella infection associated with?

A
  • Contaminated food e.g. poultry, eggs, & dairy products

- Human to human transmission is unlikely

27
Q

What are the clinical manifestations of Small Intestine Nontyphoidal Salmonella?

A

Clinical manifestations occur between 6 & 48 hours post-ingestion:

  • Nausea & vomiting
  • Abdominal cramps
  • Watery diarrhea

This persists for 3-4 Days, & typically there is spontaneous resolution in 7 days

28
Q

Describe the mechanism of action of Small Intestine Nontyphoidal Salmonella.

A

Same as Salmonella typhi with Type III Secretion System

29
Q

How is Small Intestine Nontyphoidal Salmonella diagnosed?

A

Serology
- Anti-Vi antigen antibodies

Culture from blood and stool

  • Non-lactose= white on MacConkey
  • Black precipitate b/c H2S producer
30
Q

How is Small Intestine Nontyphoidal Salmonella treated?

A

Supportive

*Abx therapy is NOT recommended unless there is systemic infection. Abx tend to enhance the carrier state

31
Q

List the characteristics of Campylobacter jejuni.

A

Gram negative “sea-gull or comma” shaped
Microaerophilic
Invasive

32
Q

What disease does Campylobacter jejuni cause?

A

Ulceration
Acute enteritis
Sepesis
Guillian-Barre Syndrome

33
Q

What is the most common cause of bacterial diarrhea?

A

Campylobacter jejuni

34
Q

What syndrome is a sequalea of Campylobacter jejuni infection?

A

Guillian-Barre Syndrome

35
Q

What is Guillian-Barre Syndrome?

A

Acute immune-mediated polyneuropathy

  • Progressive & fairly symmetric muscle weakness
  • Absent or depressed deep tendon reflexes
36
Q

How is Campylobacter jejuni diagnosed?

A

Culture (microaerophilic environment)

37
Q

How is Campylobacter jejuni treated?

A

Supportive therapy

Antibiotic therapy

Microbiology (49 decks)

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