3. Gastrointestinal Infections Flashcards
Purpose of buffered glycerol
Transport best for Shigella
Infections due to this organism are NOT treated empirically
Shigella
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.
b) Carbohydrates in the medium can cause autoagglutination
Humans and large primates are the only reservoir of this organism
Shigella
Name of watery diarrhea w/ fleck of white-ish material (mucous + GI epithelial cells)
Which organism causes it?
Rice water stools
Vibrio cholera
E. coli acronym that causes HUS
EHEC
AKA Shiga-toxin producing E. coli
EHEC (STEC)
If a bloody stool is received, an aliquot is always sent for investigation for other pathogenic toxin-producing E. coli where?
- BCCDC
- On site if molecular techniques available
Liquid media suitable for H. pylori?
Urea broth
Pathogen detected by TCBS
Vibrio
Green colony on TCBS = which organism?
Vibrio parahemolyticus
Yellow colony on TCBS = which organism?
Vibrio cholerae
What is Reiter’s syndrome
Reactive arthritis caused by Campy as well as Chlamydia
Pathogen detected by XLD agar
Shigella spp, Salmonella spp.
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(-)
d) ONPG(-), glucose(+), lysine(-), motility(-)
2 viruses that cause diarrhea
- Rotavirus
- Norwalk virus
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
b) Rotavirus
* This virus is an important worldwide cause of diarrhea in infants and young children.*
Stool transport media that can be stored/transported at RT
Cary-Blair transport medium
Which ingredient in Hektoen agar would be considered differential?
Bile salts
Yeast extract
Ferric chloride
Salicin
Salicin
Three carbohydrates are present to differentiate between different enteric organisms; lactose, sucrose, and salicin.
E. coli acronym that causes traveler’s diarrhea
ETEC
Pathogen detected by CIN agar
Yersinia
Most common serotype of Shigella in North America
Sh. sonnei (Group D)
E. coli acronym that is not invasive and produces no toxin
EPEC
PVA preservative cannot be used in the investigation of this organism
Cryptosporidium
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
c) Toxin B only
- The cytotoxin assay detects toxin B.
- EIA and latex tests detect toxins A and/or B.
AST usually tested but not reported for this organism
Salmonella spp.
Which of the following tests best differentiates Salmonella sp.from Citrobacter sp.?
H2S production
Phenylalanine deaminase
Lysine decarboxylation
Citrate utilization
Lysine decarboxylation
This test differentiates these organisms since Salmonella sp. are lysine positive and Citrobacter sp. are negative.
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
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.*
If Salmonella only has agglutination with the Vi antiserum, what should be done?
Boil for 10 mins, re-test the polyvalent O antiserum
Campylobacter catalase result?
Catalase POS
Characteristic that separates Plesiomonas from the rest of the Enterobacteriaceae family
Oxidase POS
What is SAF preservative in Ova and Parasite collection?
Sodium acetate, acetic acid, formalin
What is PBS broth used for
Yersinia cold enrichment
Rarest and most virulent Shigella
Sh. dysenteriae (Group A)
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
All of the above
All specific bacterial and viral stool pathogens are reportable to Public Health in British Columbia
pH indicator in TSI
Phenol red
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
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.
What is the purpose of using an enrichment media in stool cultures?
Suppress growth of coliforms while allowing Salmonella and Shigella to grow
3 parasites that cause diarrhea
- Giardia lambia
- Cryptosporidium spp.
- Entamoeba histolytica
