Enteropathogens

Question 1

What are the 4 F’s for transmission of most enteropathogens? How is this clinically significant?

Answer 1

Feces, Fingers, Flies and Food (and water);
Water quality and food sanitation is a major focus of public health to prevent outbreaks (greater frequency outside of the US)

Question 2

What are the 3 antigens that are essential in serotyping organisms?

Answer 2

(H) Flagella, (O) LPS, (K) Kapsule

Question 3

How is serotyping used in epidemiology of food poison outbreaks? Provide an example.

Answer 3

Serotyping enables scientists to trace back common serotypes coming from food chains that may distribute their contaminated products over a large area. For instance, a specific E. Coli serotypes can be traced back to a supply chain.

Question 4

What are the 2 toxins of Enterotoxigenic E. coli (ETEC)? What is the major disease of this E. coli?

Answer 4

1. Labile toxin made in lower amounts; resembles cholera toxin
2. Stable Toxin; analogue of gut peptide hormone; stimulates Guanyl cyclase;
   A major disease is Inflammatory enteritis where the high cAMP levels = diarrhea as in cholera

Question 5

Describe the Type 3 system in Inflammatory Enteritis.

Answer 5

This is a method in which ETEC attaches to epithelial cells and injects toxins into them to induce their own phagocytosis like a molecular syringe

Question 6

Describe some features of EPEC.

Answer 6

Adhere to enterocytes and activates Type III secretion to cause cytoskeletal rearrangement, to form CUPPED PEDESTALS. In these infections, the brush border disappears.

Question 7

What organism causes Bacillary dysentery? Describe the symptoms involved.

Answer 7

Shigella which is similar to Shiga toxin producing E. Coli (STEC) produces Bacillary dysentery. This features painful, bloody low volume stools and abdominal cramps.

Question 8

Describe the MOA by which STEC or Shigella infects enterocytes.

Answer 8

1. Transcytosed by M cells
2. Invade enterocytes from basal surface
3. Enter cytosol to induce ACTIN POLYMERIZATION
4. Growing actin pushes bacteria into ADJACENT CELLS through PM
5. This spreads the infection laterally

Question 9

What are the local and systemic effects of Shiga toxin?

Answer 9

Local GI effect produces dysentery, but if systemic, this causes Hemolytic-uremic syndrome (HUS). HUS involves microvascular damage in the kidney and RBC lysis.

Question 10

How does Shigella differ from STEC?

Answer 10

Shigella spreads from human to human; whereas STEC spreads from animals (i.e. cattle) to humans. Although they both elicit similar symptoms.

Question 11

Describe the mechanism by which non-typhoidal Salmonella cause disease.

Answer 11

Use M cells to exit the lumen, invade enterocytes then multiply. They cause macrophages to undergo apoptosis via Type III system. This results in non-bloody diarrhea, fever and vomiting.

Question 12

Describe the 2 ways in which Helicobacter pylori escapes stomach acid.

Answer 12

1. Lives below the mucus layer

2. Secretes urease to convert urea to ammonia (basic env.)

Question 13

Describe the ways to diagnose/treat H. pylori.

Answer 13

Diagnosis: Gastric biopsy, breath test (radio-labeled urea breathed in > collect exhaled CO2 for detection), stool antigen assays;
Treatment: antibiotics as a mainstay

Question 14

Describe why doctor’s might be worried about a young child recently treated for Typhoid fever?

Answer 14

The treated child may be in a chronic carrier state in which typhoidal salmonella can reside in the gall bladder and the child can spread this infection to other children in daycare per se.

Question 15

What is the significance about the virulence factor for Urinary tract E. Coli (UTEC)?

Answer 15

P-fimbrae which is an adhesive pili enables the bacteria to adhere to UT epithelium.

Question 16

Describe 3 unique features of E. Coli K1 that enable it to cause sepsis and meningitis.

Answer 16

1. S fimbrae - adhere to endothelium and choroid plexus (meningitis)
2. K1 capsule - Salic acid polymer that doesn’t activate complement (evades immune system)
3. Iron-acquisition systems (takes iron from host for survival)

Question 17

What are 3 types of nosocomial pathogens and how are they significant?

Answer 17

1. Enterobacter spp - antibiotic resistance mechanisms
2. Klebsiella spp. - encapsulated, MDR, necrotizing pneumonia, thick bloody sputum
3. Serration - colonies with red pigment, MDR
   * These can rapidly colonize hospital patients and are often more resistant than community-acquired strains.*

Question 18

This is a Gram-negative rod bacteria that presents in a patient as: watery Traveler’s diarrhea, heat-labile toxin (~like cholera toxin) and heat-stable toxin (~stimulates cGMP).

Answer 18

Enterotoxigenic E. coli (ETEC)

Question 19

This is a Gram-negative rod bacteria that presents in a patient as: blood diarrhea, low platelet count and O157:H7 antigen found in undercooked meats.

Answer 19

Shiga toxin producing E. coli (STEC or EHEC)

Question 20

This is a Gram-negative rod species that adheres to enterocytes and uses Type III secretion system to rearrange the cytoskeleton to create a cupped pedestal for the bacterium.

Answer 20

Enteropathogenic E. coli (EPEC)

Question 21

List at least 3 facts about E. Coli that cause diarrhea.

Answer 21

1. Ferment lactose (appear pink on MacConkey agar)
2. Catalase positive
3. Fimbriae make it the # 1 cause of UTI and Gram-negative sepsis.

Question 22

This bacteria is comma-shaped, acid-labels, oxidase positive, causes rice-water diarrhea and secretes a toxin that increases cAMP levels. What is it and how is it treated?

Answer 22

Vibrio cholerae secretes cholera toxin that increases Adenylase cyclase, cAMP, Cl- efflux and creates a water gradient. It is treated with Oral Rehydration Therapy, tetracycline/ampicillin antibiotics.

Question 23

This type of Gram-negative bacterium penetrate enterocytes, induces apoptosis in macrophages via Type III system and causes “non-bloody diarrhea”.

Answer 23

Non-typhoidal Salmonella

Question 24

This gram-negative bacterium has a curved, Gullwing morphology, secretes cytotoxin, and cross-reaction of its proteins can mount an immune response on CNS proteins.

Answer 24

Campylobacter jejuni

Question 25

What are the 3 curved, gram-negative rods that are all oxidase positive? Briefly describe each.

Answer 25

1. Campylobacter jejuni - common cause of bloody diarrhea, oxidase-positive, Guillian Barre syndrome; from poultry
2. Vibrio cholerae - cholera toxin increases cAMP to cause rice-water diarrhea; from shellfish
3. Helicobacter pylori - urease-positive, helical bacteria in pylorus of stomach, cause of duodenal (peptic) ulcers, MALT lymphoma

Question 26

What are the 3 treatment strategies for H. Pylori infection?

Answer 26

1. Proton pump inhibitor
2. Bismuth salt
3. Amoxicillin and Clarithromycin antibiotic

Question 27

Describe at least 5 features of Yersinia Pestis (and enterocolitica)

Answer 27

1. Cause of Bubonic plague - buboes or swollen lymph nodes
2. Enterocolitica Mimics appendicitis (RLQ pain)
3. Grows at 4 C in refrigerated foods (i.e. milk)
4. Prairie dogs/rodents are the reservoir in the US
5. Type III system prevents phagocytosis

Question 28

List 3 important features of Salmonella Typhi.

Answer 28

1. Capsule is the virulent antigen
2. Penetrate M cells and multiply inside Macrophage phagocytic vacuoles
3. Chronic carrier state in gallbladder (enables carriers like Typhoid Mary to shed Salmonella for years).

Question 29

Briefly describe the MOA of ETEC resulting in diarrhea.

Answer 29

Secretes powerful exotoxins that stimulate fluid secretion into intestines (heat-labile and heat-stable toxins).

Question 30

What is the virulence factor of UTEC that enables it to cause UTI’s?

Answer 30

Pili that adhere to the urethra wall and lining of urinary tract.

Question 31

This Gram-negative bacterium results in cramping, watery stools, anemia, thrombocytopenia and fragmented RBCs. What is it and what does it secrete?

Answer 31

Shigella sonnei secretes Shiga toxin which binds the 60S ribosomal subunit of host to inhibit protein translation. It also works via Type III Secretion system.

Question 32

What common virulence factor enables some mucosal colonizer bacteria to escape the immune system’s defenses?

Answer 32

IgA Protease (found in Haemophilus influenzae)

Question 33

What enteropathogen causes watery diarrhea with flecks of mucus without febrility and dehydration?

Answer 33

Vibrio cholerae

Question 34

Salmonella typhi spreads via intracellular multiplication within what type of cell?

Answer 34

Macrophages and monocytes.