Topic 1-12 (Lecture 12)

Question 1

What are the general characteristics of Vibrio cholerae?

i.e motility, Gram pos/neg, Shape, external features

Answer 1

Motile
gram-negative
Curved rod (vibriod)
Single, polar flagellum

Question 2

Where are vibrio cholerae found?

Answer 2

Survive in humans, fresh or brackish water

Question 3

Vectors of cholera?

Answer 3

Only humans; no insect vector or animal reservoir

Question 4

How are V. cholerae strains serotyped (identified)?

Answer 4

Based on LPS O antigen

Question 5

What serogroups of V. cholerae are responsible for cholera outbreaks?

Answer 5

O1 and O139 serogroups

Question 6

What are the major virulence factors of V. cholerae?

Answer 6

Cholera toxin
Tcp pili
Flagellum (motility)

Question 7

How is cholera spread?

Answer 7

oral ingestion of fecal-contaminated water & food (fecal-oral route) (often linked w/ poor sanitation);

Question 8

How often does the disease tend to appear?

Answer 8

Appears in epidemics

Question 9

What type of individuals are susceptible to cholera?

Answer 9

All individuals are susceptible; however, those with damaged/underdeveloped immunity, reduced gastric acidity, or malnutrition may suffer from more severe forms of the illness

Question 10

What is the incubation period of chloera?

Answer 10

6 hours to 5 days

Question 11

What causes the disease?

Answer 11

An enterotoxin (type of exotoxin) called cholera toxin (CT) which causes massive diarrhea (loss of 20L/day of fluids)

Question 12

What are the symptoms?

Answer 12

Watery diarrhea containing mucus, epithelial cells (“rice-water stool”) and lots of bacterial vibrios (cell shape is vibroid)

Question 13

What are complications associated with diarrhea caused by cholera?

Answer 13

Severe fluid and electrolyte loss → dehydration, anuria (lack of urination), acidosis (in blood), and shock

Possible muscle cramping, nausea, vomiting ,fever

Loss of K+ ions leading to possible cardiac complications and circulatory failure

Question 14

How is cholera diagnosed?

Answer 14

Gastrointestinal symptoms
Presence of rice water stool

Confirmation by isolation of Vibrio cholarae from stool (Think of Koch’s postulates)

Question 15

What is the main potent toxin of V. cholorae?

Answer 15

Cholera toxin (CT)
Those who do not produce CT may still cause disease, but a milder form that is caused by other toxins

Question 16

What is the structure of CT? (cholera toxin)

Answer 16

Multimeric protein consisting of 5 identical binding proteins (“B”) and one enzymatic subunit (“A”) - thus called an AB5 toxin

Question 17

What is the action of the AB5 toxin? (in steps)

Answer 17

1) A B subunit binds to GM1 ganglioside (a glycolipid receptor) on an intestinal epithelial cell membrane
2) CT endocytosis and passes through endomembrane (To golgi, to ER) where A portion enture cytosol
3) A unit activates adenylate cyclase which converts ATP to cAMP
4) cAMP stimulates protein kinase A (PKA) which phsophorylates cystic fibrosis transmembrane regulator (CFTR)
5) CFTR stimulates secretion of Cl- ions, which further stimulate K+ and bicarbonate ions (due to osmosis)
6) Change in ion concentration due to electrolyte loss results in water entering lumen through via osmosis
7) Toxin-damaged cells become pumps for water and electrolytes (constantly being replenished via blood flow) resulting in diarrhea, dehydration, and the massive loss of electrolytes

Question 18

What host defence plays a large role in preventing cholera infection?

Answer 18

Gastric acidity; V. cholarae are sensitive to acid pH

Question 19

What are implications of V. cholerae’s acid intolerance?

Answer 19

Large ID50 required to produce disease (since gastric acidity can kill the bacteria)

Those with poor health or gastric abnormalities are more easily infected

Consumption of food or antacid may provide protection of the bacteria (by raising pH)

Question 20

What area of the body is the V. cholerae well adapted to survive in?

Answer 20

Small intestine

Question 21

What adaptations help V. cholerae colonize the small intestine?

Answer 21

Resistant to bile salts
Can adhere to & penetrate mucous layer of small intestine
WIthstand propulsive gut motility (peristalsis of gut to move food along) using its motility and chemotaxis against gut mucosa

Question 22

What determinants affect the colonization of V. cholerae?

Answer 22

Tcp (toxin co-regulated pili) that appears to cause aggregation of bacteria (bacteria w/o tcp are not pathogenic)
acf genes (accessory colonization factor) may be required to mediate binding

Question 23

How is cholera treated?

Answer 23

Rapid replacement of fluids, either through oral rehydration w/ water, salts and glucose mix (like Gatorade) or via intravenous re-hydration therapy for those in shock or unable to drink

Question 24

Are antibiotics useful against cholera?

Answer 24

May be helpful, but not essential - lost in stool anyways. Only help to reduce duration by reducing CT production, stool volume, and shedding of vibrios

Question 25

Is there a development of a secondary immune response to cholera?

Answer 25

Yes; Ab are formed against cholera antigens (and against toxin)

Question 26

Is there a vaccines available for cholera? If so, are they effective?

Answer 26

Yes, there are 3 available; only partially effective

Question 27

What is the most important measure in controlling cholera outbreaks?

Answer 27

Having proper sewage and water treatments

Question 28

What are precautions one can take to minimize the risk of contracting cholera?

Answer 28

Drinking boiled or treated water
Not having drinks with ice
Eating only cooks that are thoroughly cooked and are hot
Eating only peeled fruit
Avoiding undercooked/raw fish/shellfish
Eating only cooked vegetables (avoid salads)
Not eating foods from street vendors

“Boil it, cook it, peel it, or forget it”

Question 29

What is the importance of biofilms in relation to V. cholarae?

Answer 29

Biofilm formation critical for its survival and transmission

-can form biofilms anywhere, but often in crustaceans and freshwater habitats

Question 30

How is biofilm production regulated in V. cholerae?

Answer 30

Biofilm producing genes turned ON upon exiting host

Biofilm producing genes turned OFF upon entering host