Enterobacterales Flashcards
What is the Gram stain of enterobacterales?
Gram-negative
What do enterobacterales refer to?
It is an order that contains 7 families
How do enterobacterales respond to an oxidase test?
It will be negative
What are the common characteristics of enterobacterales?
Inhabit human and animal GI tracts
Common in nature
Facultative anaerobes
Motility variable
Glucose fermenters
Oxidase-negative
Not fastidious
How do enterobacterales cultures look compared to Gram-positive cultures?
Enterobacterales colonies ted to be big while Gram-positive colonies are much smaller in comparison
What is the typical Gram stain morphology of enterobacterales?
Medium-sized Gram-negative bacteria with rounded ends
Some are short rods that resemble Gram-negative coccobacilli
Often stains better on the ends = bipolar staining
What are the relevant opportunistic enterobacterales pathogens?
Salmonella spp (non-Typhi)
E. coli
What are the relevant overt enterobacterales pathogens?
Salmonella Typhi
Shigella spp
E. coli
What are some infections caused by enterobacterales?
Neonatal meningitis
Bacteraemia
Liver abscesses
Abdominal wounds
Lower respiratory tract
Diarrhea
Urinary tract
How does E. coli colonize humans?
It colonizes infants at birth and exists in a mutually beneficial relationship with the host and remains confined to the intestinal lumen
How does E. coli cause disease?
It causes disease in immunocompromised patients or can be introduced via surgery/trauma
How is E. coli transmitted?
Endogenous, fecal-oral, person-to-person, contaminated food/water
What is enterotoxigenic E. coli?
Traveler’s diarrhea = watery stools
Virulence factors = heat labile and heat stable toxins
What is enteroinvasive E. coli?
It invades enterocytes; similar to Shigella
Causes dysentery in young children
What is enteropathogenic E. coli?
Causes diarrhea in infants and chronic diarrhea
What is enterohemorrhagic E. coli?
Produces Shiga toxin which targets endothelial cells in the GI tract and kidneys
Causes hemorrhagic colitis
Causes hemolytic-uremic syndrome
What is uropathogenic E. coli?
Causes extraintestinal infections (UTIs)
Community-acquired
What does enteroaggregative E. coli cause?
Watery diarrhea
What does Salmonella do?
Causes infections in humans and cold-blooded animals
What does non-typhoidal Salmonella cause?
Gastroenteritis = diarrhea, fever, cramps with a wide variety of serotypes
Bacteremia, extraintestinal infections = spread from GI tract, immunocompromised
What does typhoidal Salmonella cause?
Typhoid fever = prolonged fever, multisystem involvement
fecal-oral infection
Which species of Salmonella causes infection in warm-blooded animals?
S. enterica
When we refer to Typhi what do we mean?
It is a Salmonella serotype, not a genus
What is the onset and symptoms of Salmonella infections?
Symptoms occur within 6-72 hours of exposure
Symptoms = fever, chills, diarrhea, abdominal cramps, headache, nausea, vomiting
Who is most at risk for Salmonella infections?
Children younger than 5
Older adults
Pregnant women
Those who are immunocompromised
How is Shigella transmitted?
Transmitted person-to-person and ingestion of contaminated food/water
Shigellosis is most common in situations where hygiene is compromised
How is Shigellosis characterized?
By bloody diarrhea and non-bloody diarrhea
How is Shigella different from E. coli and Salmonella?
It is not motile so it cannot easily access the bloodstream
PulseNet Canada plays a vital role in what?
Active surveillance and investigation of foodborne outbreaks
How do we serotype E. coli?
By its O antigen (186 types) and its H antigen (56 types)
What is the most common Shiga toxin producer?
O157:H7
How do we serotype Shigella?
4 subgroups (A-D) and many serotypes
How do we serotype Salmonella?
Based on characterization of O, H, and Vi antigens
How do we test for lactose fermentation?
Use MacConkey agar
If the plate turns red, that means that the bacteria produced acid
Bile salts and crystal violet inhibit most Gram-positives
What are 4 lactose fermenters?
Citrobacter
E. coli
Enterobacter
Klebsiella
What are non-lactose fermenters within Enterbacterales?
Salmonella
Shigella
What is indole used for?
To determine if the organism can convert tryptophan to indole
It turns pink if indole is present
What is a relevant enterobacterales that produces H2S
Salmonella
What are the biochemical characteristics of E. coli?
Colony characteristics: LF, some beta-hemolysis
Indole = +
H2S = -
Motility = +
What are the biochemical characteristics of Salmonella?
NLF, black on HE agar
Indole = -
H2S = +
Motility = +
What are the biochemical characteristics of Shigella?
NLF, colorless on HE agar
Indole = variable
H2S = -
Motility = -
What are some primary stool culture media?
Blood agar
MacConkey agar
MacConkey-Sorbitol agar
Hektoen agar
CIN agar
Campy-CVA or Campy CBF
TCBS
What is the purpose of a blood agar media in stool tests?
Rules out Aeromonas and Plesiomonas
Sweep oxidase test and sub-culture
This is a non-selective test
What is the purpose of MacConkey agar in stool tests?
Contains bile salts and crystal violet which inhibits Gram + bacteria
Tests for lactose fermentation
Selective and differential medium
What is the purpose of MacSorb agar in stool tests?
Used to enhance isolation and differentiate E. coli O157:H7 from other E. coli because this serotype does not ferment sorbitol while others do
What is the purpose of Chromogenic agar in stool tests?
Detects Shiga toxin-producing E. coli of all serotypes
What is the purpose of Hektoen agar in stool tests?
Selects for stool pathogens by inhibiting normal flora of the gI tract
What is the purpose of CIN agar in stool tests?
Used to isolate Yersinia spp
What is the purpose of Campy-CVA agar in stool tests?
Isolation of Campylobacter spp
What is the purpose of TCBS agar in stool tests?
Selective and differential for Vibrio species
What are the advantages of molecular testing for GI pathogens?
Fast, tests a broad range of organisms
What are the disadvantages of molecular testing for GI pathogens?
Sensitivity, limited to the panel targets, can be expensive
