Infectious Diarrhea

Question 1

Which bacteria can survive the acidic pH of the stomach?

Answer 1

Acid-tolerant lactobacilli and streptococci

Question 2

What type of bacteria predominates the large intestine?

Answer 2

Anaerobic bacteria

Question 3

WHO’s definition of diarrhea:

Answer 3

passing of liquid or watery stools at least 3 times in a 24-hour period
(consistency of stool is more important than frequency)

Question 4

Amoebic dysentery is caused by:

Answer 4

Entamoeba

Question 5

Bacillary dysentery is caused by:

Answer 5

Shigella

Question 6

Infectious diarrhea is the second leading cause of death in:

Answer 6

Children under 5 yrs old - also the leading cause of malnutrition

Question 7

Common viral agents causing diarrhea:

Answer 7

Rotavirus (RNA) Norovirus, Enteric Adenovirus (DNA; types 40 and 41.)

Question 8

Common bacterial agents causing diarrhea:

Answer 8

E. coli
Campylobacter
Salmonella
Shigella

Question 9

Common protozoal agents:

Answer 9

Entamoeba histolytica
Giardia spp.
Crytposporidium parvum

Question 10

E. coli strains are classified based on:

Answer 10

The clinical symptoms they cause

Question 11

The two types of enterotoxins produced by Enterotoxigenic E. coli (ETEC) are:

Answer 11

• LT (heat labile toxin)

- ST (heat stable toxin)

Question 12

The heat labile toxin produced by ETEC is related to which other toxin?

Answer 12

Cholera toxin

Question 13

The heat labile toxin produced by ETEC acts via:

Answer 13

increasing intracellular conc of cAMP –> secretion of Cl- from intestinal crypt cells –> inhibition of NaCl absorption –> accumulation of fluid within lumen

Question 14

Heat stable ETEC toxin inc the intracellular conc of:

Answer 14

cGMP

Question 15

The virulence factor at the center of the pathology of Enteropathogenic E. coli is:

Answer 15

Intimin (adhesion) –> attaching and effacement lesions. Causes a blunting (effacement) of microvilli

Question 16

Enterohemorrhagic E. coli produces the following toxin:

Answer 16

Shiga toxin

Question 17

Which EHEC serotype has been associated with large outbreaks?

Answer 17

EHEC serotype O157:H7

Question 18

EHEC serotype O157:H7 is associated with the following syndrome:

Answer 18

Hemolyitc uremic syndrome (progressive renal failure, hemolytic anemia, thrombocytopenia)

Question 19

Enteroinvasive E. coli has a virulence factor called:

Answer 19

Invasin (allows the organism to penetrate the enterocytes)

Question 20

E. coli properties:

Answer 20

oxidase negative
indole positive
lactose fermenting

Question 21

How can you differentiate between pathogenic and non-pathogenic strains of E. coli?

Answer 21

Sorbitol MacConkey agar. Pathogenic E. coli CANNOT ferment sorbitol.

Question 22

Campylobacter properties:

Answer 22

Microaerophilic
Thermophilic
Chicken/chicken products can harbor the organism

Question 23

An acute episode of Campylobacter infection is characterized by:

Answer 23

abdominal cramps
periumbilical abdominal pain
diarrhea

Question 24

Campylobacter lab features:

Answer 24

Gram neg. curved bacilli

oxidase positive

Question 25

Shigella causes:

Answer 25

Bacillary dysentery - only a low infective dose is required for infection

Question 26

The most virulent Shigella spp:

Answer 26

S. dysenteriae (serogroup A)

Question 27

The Shigella spp. that is most commonly implicated in DEVELOPING countries:

Answer 27

S. flexneri (serogroup B)

Question 28

The Shigella spp. that is most commonly implicated in DEVELOPED countries:

Answer 28

S. sonnei (serogroup D)

Question 29

Shiga toxin is produced by which Shigella spp?

Answer 29

S. dysenteriae

Question 30

Pathology of Shigella:

Answer 30

Death of epithelial and immune cells + formation of colonic mucosal ulcerations and abscesses

Question 31

Dysenteric stool of patients with shigellosis contains:

Answer 31

blood, mucus and small amounts of fecal matter

Question 32

Lab features of Shigella:

Answer 32

gram-negative bacilli
facultative anaerobe
oxidase negative
non-lactose fermenter on MacConkey agar

Question 33

Which Salmonella spp is associated with 99% of salmonella infection?

Answer 33

Salmonella enterica

Question 34

Salmonella has three major antigens:

Answer 34

1. H - flagellar antigen
2. O - somatic antigen
3. Vi antigen (in S. typhi and S. paratyphi)

Question 35

Salmonellosis:

Answer 35

Caused by: S. enterica serovars Typhimurium & Enteritidis
No human reservoir
Mild and self-limiting

Question 36

Typhoid fever:

Answer 36

S. enterica serovar Typhi & Paratyphi
Human reservoirs present
Carrier state
Can spread hematogenously to other organs

Question 37

Salmonella lab features:

Answer 37

Gram neg. bacilli 
Oxidase negative 
Facultative anaerobe 
Selenite F Broth medium (enrichment) 
Non-lactose fermenter on MacConkey agar

Question 38

What type of virus is Rotavirus?

Answer 38

RNA virus

Question 39

What is the most common cause of acute gastroenteritis in children under the age of 2?

Answer 39

Rotavirus infection. Nearly every child has at least 1 rotavirus infection by 5 years of age.

Question 40

Rotavirus secretes the following toxic protein:

Answer 40

NSP4 (causes villi atrophy, loss of digestive enzymes, and reduction of absorption)

Question 41

Rotavirus vaccines:

Answer 41

2 available vaccines
All doses of vaccine must be given (orally) before 8 months
1st dose should be given before 15 weeks of age

Question 42

The diagnosis of rotavirus is mainly:

Answer 42

a clinical diagnosis

Question 43

Norovirus causes:

Answer 43

acute diarrhea - infection spreads in crowded areas (nursing homes, cruise ships and dorms)

Question 44

Enteric adenovirus is a:

Answer 44

DNA virus (double stranded) with a nucleocapsid 
non-enveloped icosahedral particle