GI Pathogens

Question 1

What gram-positive, non-spore forming rod that is catalase positive and beta-hemolytic on blood agar has a characteristic tumbling motility?

Answer 1

Listeria monocytogenes

Question 2

What are 5 methods of obtaining a Listeria monocytogenes infection?

Answer 2

1. Ingestion of contaminated raw milk or cheese from infected cows
2. Undercooked processed meats
3. Unwashed raw vegetables
4. Vaginally (during birth)
5. Transplacental infection of fetus from bacteremic mother.

Question 3

What are the 3 characteristics of L. monocytogenes morphology?

Answer 3

1. Gram-positive rod
2. Non-spore forming
3. Motile - tumbling motility at 25C

Question 4

What are 3 characteristics of L. monocytogenes metabolism?

Answer 4

1. Facultative anaerobe
2. Catalase - positive
3. Beta-hemolytic

Question 5

1. How does *L. monocytogenes *create its movement? What antigen is associated with this?
2. What creates its heomlytic capability? What properties does this substance have?

Answer 5

1. It has flagella, so it has H-antigen
2. Hemolysin (similar to streptolysin-O). It is heat labile and antigenic.

Question 6

1. What two toxins does L. monocytogenes secrete?
2. What do these toxins do?

Answer 6

1. Listeriolysin O and phospholipases
2. Allows escape from phagolysosomes of macrophages.

Question 7

What are three clinical conditions that can develop from L. monocytogenes?

Answer 7

1. Neonatal meningitis
2. Meningitis in immunosuppressed patients and the elderly.
3. Septicemia in pregnant women (usually during 3rd trimester when immune system is weakest)

Question 8

1. What is the appropriate antibiotic treatment for L. monocytogenes?
2. What is it naturally resistant to?

Answer 8

1. Gentamycin & Penacillin/Ampicillin combination therapy.
2. Naturally cephalosporin resistant

Question 9

What are the two CDC associated outbreaks of Listeria from?

Answer 9

Cantaloupes and Ricotta cheese

Question 10

*Listeria *becomes less motile by flagella at 37C and higher, so how does it move through the host cell?

Answer 10

It develops an ActA based actin polymerization using the host’s cytoskeleton. This acts like a “comet tail”

Question 11

1. Is the normal gastroduodenal environment sufficient to sterilize L. monocytogenes?
2. Listeria is a facultative intracellular parasite, what cells does it first enter and where?
3. What stimulates the activity of listeriolysin O and Listeria’s phospholipases?
4. Where does L. monocytogenes freely replicate?

Answer 11

1. No, it can survive both gastric acid and bile salts.
2. Enterocytes or M-cells in Peyer’s patches.
3. A drop in pH in the phagosome.
4. In the cytoplasm.

Question 12

How is L. monocytogenes isolated from mixed flora in culture?

Answer 12

It can grow at temperatures as low as 2.5C. So using a cold enrichment technique will isolate it.

Question 13

1. Where is Salmonella typhi found?
2. Where are non-typhi Salmonella groups found?
3. By what route is S. typhi transmitted?

Answer 13

1. Only in humans
2. Pet turtles - Chickens - undercooked eggs
3. Fecal - Oral

Question 14

What morphology do the Enterobacteriaceae family bugs, Salmonella, Shigella, and E. coli have in common?

Answer 14

They are all Gram negative rods

Question 15

What metabolic characteristic differentiates *E. coli *from *Salmonella *or Shigella?

Answer 15

E. coli ferments lactose and the others do not

Question 16

If Shigella and Salmonella are both non-lactose fermenting what metabolic trait differentiates them?

Answer 16

Salmonella produces H₂S and Shigella does not produce it.

Question 17

What serologic antigens would a Salmonella infection be positive for and what do they represent? (3 items)

Answer 17

H antigen - flagellar proteins

VI antigen - capsular proteins

O antigen - LPS

Question 18

Which of the three Enterobacteriaceae organisms for this course is a siderophore?

Answer 18

Salmonella

Question 19

What toxins is Salmonella associated with?

Answer 19

None

Question 20

1. What are the clinical hallmarks of S. typhi related typhoid fever?
2. How does S. typhi spread to other locations?

Answer 20

1. Fever - Abdominal pain - Hepatosplenomegaly - Rose spots on abdomen
2. Through the reticuloendothelia system

Question 21

How does non-typhi Gastroenteritis create its symptoms?

Answer 21

Induction of inflammatory response
Disruption of enterocytes → malabsorption
Release of PGs → increase in cAMP → watery diarrhea

Question 22

1. Is there a typhoid vaccine? What type of vaccine is it?
2. What is the anti-biotic treatment for a Salmonella infection?
3. Should all Salmonella infections be treated with anti-biotics?

Answer 22

1. There are two - A live attenuated vaccine Ty21a and a VI polysaccharide vaccine, Typhim.
2. Ampicillin & Bactrim or Cipro
3. No, gastroenteritis only infections should not

Question 23

How would you obtain a culture of S. typhi from a suspected patient?

Answer 23

From stool

Question 24

S. typhi is a facultative intracellular parasite that can live in carriers for years. Where does it hide out?

Answer 24

In the gallbladder. *S. typhi *is shed in carriers stool (Typhoid Mary)

It can also live within macrophages in lymph nodes

Question 25

What type of people are at increased risk of having a clinically significant *Salmonella* infection?

Answer 25

People who are **asplenic** (particularly SCD patients)

Question 26

How is *Shigella* different from *Salmonella* metabolically?

Answer 26

*Shigella* **does not produce H₂S.**

Question 27

1. What intestinal cells does *Shigella* invade? 2. How does it promote its own engulfment? 3. Where in the cell does it replicate? 4. How does *Shigella* promote intestinal inflammation?

Answer 27

1. M cells of Peyer's patches 2. Injects type III "effectors" w/ instructions for engulfment (These "effectors" are **_I_**nvasion **_P_**rotein **_A_**ntigens, IpaA,B,C,D) 3. In the cytoplasm 4. *S. dysenteriae* induced apoptosis releases **IL-1**

Question 28

1. What are the clinical symptoms of a *Shigella?* 2. What is the treatment? 3. What is the only reservoir for *Shigella?* 4. Why should anit-diarrheals be avoided?

Answer 28

Bloody diarrhea with mucus and pus 2. Ampicillin, Bactrim, Ceftriaxone 3. Humans 4. They worsen illness by trapping toxin in gut.

Question 29

How long after ingestion of *Shigella* do symptoms develop?

Answer 29

1-3 days

Question 30

What are metabolic commonalities between all enterobacteriaceae?

Answer 30

All are: 1. Catalase-positive 2. Oxidase-negative 3. Ferment glucose 4. Facultative anaerobes

Question 31

What is the structural commonality of *E.coli, Shigella, *and *Salmonella?*

Answer 31

They are all Gram negative rods

Question 32

What is unique about *E. coli* metabolicaly compared to *Salmonella, *and *Shigella?* (3 items)

Answer 32

1. It is **Indole positive** (makes indole from tryptophan) 2. It is **Beta-hemolytic** 3. It **ferments lactose**

Question 33

What are 5 virulence factors for *E.coli**?*

Answer 33

1. **Fimbriae** (pili): a colonization factor 2. It is a **siderophore** 3. It has **adhesins** 4. It has a **capsule** (K-antigen) 5. It has **flagella** (H-antigen)

Question 34

What three toxins are associated with *E. coli**?* What do they do?

Answer 34

1. LT (heat labile) - increases cAMP (sames as cholera toxin) 2. ST (heat stable) - increases cGMP 3. Shiga-like toxin (verotoxin) - inhibits protein synthesis by inactivating 60S

Question 35

1. How can normal E. coli be differentiated from EHEC using MacConkey agar?

Answer 35

1. Normal E.coli will appear pink because it CAN ferment sorbitol while EHEC appears colorless because it cannot ferment sorbitol.