GI Infections - Diarrhea

Question 1

Why does diarrhea kill?

Answer 1

Immediate: Fluid and electrolyte imbalance
a) Fluid loss - impacts children much more so due to their lower blood volume
Delayed: Malnutrition
a) Increase flow of nutrients (not being able to be absorbed)
b) Inflammation of the absorptive mucosa - no exchange
c) repair mechanisms: no proteins being absorbed = no repair mechanism = leads to further malnutrition

Question 2

What is the association between Diarrhea and Malnutrition?

Answer 2

1) Increased Energy Loss:
a) Diarrhea and vomiting - energy expensive processes
b) Increased metabolic needs - due to immune response]
2) Decreased Intake
a) absorptive processes not functional - inflammation?
b) With-holding of food: the thought that food/breast milk caused the diarrhea (Breast milk is a good mechanism to help with diarrhea)

Question 3

Where does the majority of fluid uptake occur?

Answer 3

In the small intestine (upto 8.5 L / day). It also secretes water.

Question 4

What role does the LI have in water reabsorption?

Answer 4

Absorbs the remaining water from the SI - approx 1.5L. It also has a reserve capacity (5L).

Question 5

How do the rates of absorption differ between the SI and LI?

Answer 5

Small Intestine - faster rate of absorption

Large Intestine - slower rate of absorption

Question 6

What kind of diarrhea do you get if the origin is in the SI? LI?

Answer 6

SI - diffuse watery diarrhea, high frequency; overwhelms the reserve capacity of the LI.
LI - small amounts of water, usually a dysentery - blood, pus, mucus

Question 7

What kind of bacteria/virus/protozoa diarrheal distribution do you seen in: developing vs developed countries?

Answer 7

1. Developing: bacteria>viral>protozoa

2. Developed: viral>bacteria>protozoa

Question 8

Name the Diarrheal Syndromes:

Answer 8

NDF TPH CE
Non-specific Gastroenteritis, Dysentery, Foodborne, Traveller’s, Pseudomembranous Colitis, Hemmorhagic, Cholera-Like, Enteric Fever

Question 9

Name the 2 types of Dysentery and their causes

Answer 9

1. Bacillary Dysentery: Shigella Dysenteria/EIEC

2. Amoebic Dysentery: Amoebia Histolytica

Question 10

What are the prominent causes of food borne ill-ness?

Answer 10

S2V2C3 BELY
Salmonella (most common cause), Staph. Aureus (S.Ag), Vibrio Cholera, Viruses (Nora/Rota), Ciguatoxin (fish), Clostridium, Campylobacter (Chicken), Bacillus, EHEC, Listeria Yessinia

Question 11

How does Salmonella act? Where is it found?

Answer 11

Salmonella: Type 3 secretory pathway –> actin modification

Found in uncooked meats, protected by creamy products

Question 12

How does Staph. Aureus Act? How is it found in food?

Answer 12

Produces an enterotoxin that is a super antigen. Usually preformed in foods. Acts on the CNS to cause diarrhea and vomiting. Some action on the gut.

Question 13

How does Rotavirus Function?

Answer 13

Disrupts the microvilli

Question 14

How does Vibrio Cholera Function?

Answer 14

enterotoxin activates Gs → diarrhea

Question 15

Where is Camplyobacter found?

Answer 15

Zoonosis: carried by chickens. Can be contaminated after cooking – if placed on the same cutting board.

Question 16

How does Ciguatoxin function? Where is it found?

Answer 16

not infective, found in fish, lowers the threshold of the sodium gated voltage channels → leading to paralysis

Question 17

How does Clostridium function?

Answer 17

Spores are ingested - sporulation - toxin release

Question 18

How does Bacillus function?

Answer 18

Produces a toxin similar to cholera toxin.

Question 19

What is EHEC? Where is it found? What is its infective dose?

Answer 19

• Carried by cows, fecal content not destroyed due to improper cooking technique
• Low infective dose –> small number of bacteria needed to cause an infection.

Question 20

What agents cause Traveller’s Diarrhea?

Answer 20

50% of traveller’s diarrhea is caused by ETEC

Question 21

What is pseudomembranous colitis? What causes it? How is it caused? What toxins are involved?

Answer 21

i. Severest form of antibiotic associated diarrhea
ii. 20 – 33 % of the population get diarrhea due to antibiotics. Could be due to the disruption of the protective microflora OR toxic effects of the AB.
iii. C. Difficile (found in 3% of the population) takes advantage of the lack of microbiota.
iv. Produces Toxin A → binds to the brush border and Toxin B → cystoskeleton disruption leading to pseudomembranous colitis.

Question 22

What is Hemmorhagic colitis? What causes it? How is it caused? What toxins are involved?

Answer 22

EHEC, Shigella Dysteria

i. EHEC produces Shigella Toxin
ii. The stool contains mostly blood with minimal amounts of pus and mucus.
iii. Shigella can produce both dysentery and H. colitis; the other 3 shigellas only produce dysentery
iv. Shigella: Chromosomally encoded toxin
v. EHEC: plasmid encoded (phage infects the E.Coli with shiga gene)

Question 23

What is the difference between Shigella and EHEC?

Answer 23

Shigella: Chromosomally encoded toxin
EHEC: plasmid encoded (phage infects the E.Coli with shiga gene)

Question 24

What is Cholera Like Diarrhea? What causes it? How is it caused? What toxins are involved?

Answer 24

i. Vibrio: epidemic cholera caused by O1 and O139. O2-O138 are serotypes that don’t cause epidemics.
Vibrio Choleri: Phage encoded toxin
ii. Non-Vibrio: ETEC

Question 25

How is the toxin encoded in vibrio cholera?

Answer 25

Phage encoded toxin

Question 26

How are the different E.coli distinguished?

Answer 26

Different virulence factors

Question 27

What virulence factors are found on EPEC? How does it illicit its pathogenicity?

Answer 27

Bundle Forming Pili (BFP), intimins, Translocated Intimin Receptor
a. Attachment/Effacing Pathway: attachment to microvilli, actin deformation, malformation of the microvilli
b. Stage 1: Plasmid mediated: BFP allows for attachment at the microvilli
c. Stage 2: Chromosomally mediated: LEE – Pathogenicity Island
• Type 3 Secretory System: secretes TiR into the host cell via a bridge into the bacteria→ intimin binds to TiR → change in actin cytoskeleton → tight binding

Question 28

What virulence factors are found on EHEC? How does it illicit its pathogenicity?

Answer 28

a derivative of EPEC, intimins, Shiga Toxin

Question 29

What virulence factors are found on ETEC? DO they invade the mucosa?

Answer 29

Colonization Fimbrial Adhesions (CFA)
a. Attach to the mucosa, don’t invade, secrete enterotoxins:
• LT: labile
• ST: heat stable: increase cAMP → H20 secretion

Question 30

What virulence factors are found on EIEC? How does it illicit its pathogenicity?

Answer 30

Shigella like pathogenesis, IpaC

a. Plasmid encoded genes promote endocytosis → cleavage within the endosome → bacteria does damage internally

Question 31

Which bacteria are:

i. Adhesive enterotoxigenic:
ii. Adhesive with brush border:
iii. Invasion restricted to mucosa:
iv. Invasion of Submucosa:
v. Systemic Invasion:

Answer 31

i. Cholera/ETEC: no invasion
ii. EP/HEC – intimin
iii. Shigella (cell to cell mvmt)
iv. Salmonella, Campylobacter
v. Salmonella