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

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Flashcards in Exam #5: Bacterial Infections of the GI Tract II Deck (37):
1

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?

MacConkey agar= lactose fermentation

Positive= red colonies/ agar
- E. coli

Negative= white colonies/ agar
- Salmonella, Shigella

2

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 test for indole production

Positive= red
- E. coli
- Virbri

Negative= white
- Salmonella

3

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

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

- Salmonella= black (producer)
- Shigella= white (non-producer)

4

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

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

5

Describe the characteristics of EPEC.

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

6

What is EPEC associated with?

Pediatric diarrhea

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

Think P for Peds

7

Describe the mechanism of action of EPEC.

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

8

What are the clinical manifestations of EPEC?

Watery diarrhea without toxins

9

What are the morphological characteristics of EPEC?

Attaching & effacing

10

How is EPEC diagnosed?

Culture & biochemical tests
- Ferments lactose, thus it is red on MacConkey agar
- Indole positive i.e. red on indole test

PCR

11

What is the treatment for EPEC?

Supportive therapy

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

12

What are the characteristics of ETEC?

Gram negative rod
Lactose fermenter
Fast lactose fermenter
Faculative anaerobe
NOT invasive

13

What is ETEC assocaited with?

"Traveler's diarrhea"

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

14

Describe the mechanism of action of ETEC.

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

15

What is the difference between LT & ST toxins?

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

16

How is ETEC diagnosed?

- Clinically
- DNA probes to detect LT & ST

17

How is ETEC treated?

Supportive therapy

18

Describe the characteristics of Salmonella Typhi.

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

19

How is Salmonella typhi transmitted?

Human to human
Fecal to oral

20

What are the clinical manifestations of Salmonella typhi?

- Fever with headache
- Rising fever over 3 days
- Thyphoid fever
- GI symptoms

Note that there is a 13 day incubation period

21

Describe the mechanism of action of Salmonella typhi.

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

How is Salmonella typhi diagnosed?

Culture of stool and blood samples on selective media

23

How is Salmonella typhi treated?

Antibiotic therapy based on susceptibility profile

24

How is Salmonella typhi prevented?

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

Describe the characteristics of Small Intestine Nontyphoidal Salmonella.

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

What is Small Intestine Nontyphoidal Salmonella infection associated with?

- Contaminated food e.g. poultry, eggs, & dairy products
- Human to human transmission is unlikely

27

What are the clinical manifestations of Small Intestine Nontyphoidal Salmonella?

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

Describe the mechanism of action of Small Intestine Nontyphoidal Salmonella.

Same as Salmonella typhi with Type III Secretion System

29

How is Small Intestine Nontyphoidal Salmonella diagnosed?

Serology
- Anti-Vi antigen antibodies

Culture from blood and stool
- Non-lactose= white on MacConkey
- Black precipitate b/c H2S producer

30

How is Small Intestine Nontyphoidal Salmonella treated?

Supportive

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

31

List the characteristics of Campylobacter jejuni.

Gram negative "sea-gull or comma" shaped
Microaerophilic
Invasive

32

What disease does Campylobacter jejuni cause?

Ulceration
Acute enteritis
Sepesis
Guillian-Barre Syndrome

33

What is the most common cause of bacterial diarrhea?

Campylobacter jejuni

34

What syndrome is a sequalea of Campylobacter jejuni infection?

Guillian-Barre Syndrome

35

What is Guillian-Barre Syndrome?

Acute immune-mediated polyneuropathy
- Progressive & fairly symmetric muscle weakness
- Absent or depressed deep tendon reflexes

36

How is Campylobacter jejuni diagnosed?

Culture (microaerophilic environment)

37

How is Campylobacter jejuni treated?

Supportive therapy
Antibiotic therapy

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