3. Gastrointestinal Infections

Question 1

Purpose of buffered glycerol

Answer 1

Transport best for Shigella

Question 2

Infections due to this organism are NOT treated empirically

Answer 2

Shigella

Question 3

Why is the serotyping of stool pathogens not performed on growth from a MacConkey agar plate?

a) Dyes in the medium (ie., crystal violet and neutral red) can cause a false reaction
b) Carbohydrates in the medium can cause autoagglutination
c) Because you need to do an oxidase test at the same time
d) It is difficult to get isolated colonies on a MAC plate.

Answer 3

b) Carbohydrates in the medium can cause autoagglutination

Question 4

Humans and large primates are the only reservoir of this organism

Answer 4

Shigella

Question 5

Name of watery diarrhea w/ fleck of white-ish material (mucous + GI epithelial cells)

Which organism causes it?

Answer 5

Rice water stools

Vibrio cholera

Question 6

E. coli acronym that causes HUS

Answer 6

EHEC

Question 7

AKA Shiga-toxin producing E. coli

Answer 7

EHEC (STEC)

Question 8

If a bloody stool is received, an aliquot is always sent for investigation for other pathogenic toxin-producing E. coli where?

Answer 8

• BCCDC

- On site if molecular techniques available

Question 9

Liquid media suitable for H. pylori?

Answer 9

Urea broth

Question 10

Pathogen detected by TCBS

Answer 10

Vibrio

Question 11

Green colony on TCBS = which organism?

Answer 11

Vibrio parahemolyticus

Question 12

Yellow colony on TCBS = which organism?

Answer 12

Vibrio cholerae

Question 13

What is Reiter’s syndrome

Answer 13

Reactive arthritis caused by Campy as well as Chlamydia

Question 14

Pathogen detected by XLD agar

Answer 14

Shigella spp, Salmonella spp.

Question 15

Which of the following best describes Shigella sp.?

a) ONPG(-), glucose(-), lysine(+), motility(-)
b) ONPG(+), glucose(+), lysine(-), motility(-)
c) ONPG(-), glucose(+), lysine(-), motility(+)
d) ONPG(-), glucose(+), lysine(-), motility(-)

Answer 15

d) ONPG(-), glucose(+), lysine(-), motility(-)

Question 16

2 viruses that cause diarrhea

Answer 16

• Rotavirus

- Norwalk virus

Question 17

A two year-old child is hospitalized for dehydration from severe diarrhea and vomiting. What is the most likely etiological agent?

a) Clostridium difficile
b) Rotavirus
c) Vibrio cholerae
d) Hepatitis A

Answer 17

b) Rotavirus

* This virus is an important worldwide cause of diarrhea in infants and young children.*

Question 18

Stool transport media that can be stored/transported at RT

Answer 18

Cary-Blair transport medium

Question 19

Which ingredient in Hektoen agar would be considered differential?

Bile salts

Yeast extract

Ferric chloride

Salicin

Answer 19

Salicin

Three carbohydrates are present to differentiate between different enteric organisms; lactose, sucrose, and salicin.

Question 20

E. coli acronym that causes traveler’s diarrhea

Answer 20

ETEC

Question 21

Pathogen detected by CIN agar

Answer 21

Yersinia

Question 22

Most common serotype of Shigella in North America

Answer 22

Sh. sonnei (Group D)

Question 23

E. coli acronym that is not invasive and produces no toxin

Answer 23

EPEC

Question 24

PVA preservative cannot be used in the investigation of this organism

Answer 24

Cryptosporidium

Question 25

What is detected by the cytotoxin assay for Clostridium difficile? a) Toxin A and toxin B b) Toxin A only c) Toxin B only d) Toxins A, B and C

Answer 25

c) Toxin B only - The cytotoxin assay detects toxin B. - EIA and latex tests detect toxins A and/or B.

Question 26

AST usually tested but not reported for this organism

Answer 26

Salmonella spp.

Question 27

Which of the following tests best differentiates Salmonella sp.from Citrobacter sp.? H2S production Phenylalanine deaminase Lysine decarboxylation Citrate utilization

Answer 27

Lysine decarboxylation This test differentiates these organisms since Salmonella sp. are lysine positive and Citrobacter sp. are negative.

Question 28

Which of the following is true of Yersinia enterocolitica? a) It's motile at room temperatures, but not at 37°C b) It's the causative agent of bubonic plague c) It utilizes citrate d) It grows best at 42°C

Answer 28

a) It's motile at room temperatures, but not at 37°C | * All Yersinia species, other than Y. pestis, are motile at lower temperatures (22-28ºC), but is non-motile at 37ºC.*

Question 29

If Salmonella only has agglutination with the Vi antiserum, what should be done?

Answer 29

Boil for 10 mins, re-test the polyvalent O antiserum

Question 30

Campylobacter catalase result?

Answer 30

Catalase POS

Question 31

Characteristic that separates Plesiomonas from the rest of the Enterobacteriaceae family

Answer 31

Oxidase POS

Question 32

What is SAF preservative in Ova and Parasite collection?

Answer 32

Sodium acetate, acetic acid, formalin

Question 33

What is PBS broth used for

Answer 33

Yersinia cold enrichment

Question 34

Rarest and most virulent Shigella

Answer 34

Sh. dysenteriae (Group A)

Question 35

Which of the following organisms must be reported to Public Health authorities in British Columbia? Campylobacter species Salmonella species Yersinia species All of the above

Answer 35

All of the above All specific bacterial and viral stool pathogens are reportable to Public Health in British Columbia

Question 36

pH indicator in TSI

Answer 36

Phenol red

Question 37

When a stool specimen is collected for bacterial culture and will not be delivered to the lab for at least 4 hours after collection what is the best method for transport? In a clean, dry container On a swab dipped into the specimen In Cary-Blair transport medium In sodium acetate – acetic acid – formalin

Answer 37

In Cary-Blair transport medium This medium will allow the recovery of most stool pathogens and it is required anytime transport to the lab will be greater than 2 hours.

Question 38

What is the purpose of using an enrichment media in stool cultures?

Answer 38

Suppress growth of coliforms while allowing Salmonella and Shigella to grow

Question 39

3 parasites that cause diarrhea

Answer 39

- Giardia lambia - Cryptosporidium spp. - Entamoeba histolytica