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64 Cards in this Set

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  • Back
What makes E. coli famous?
Its the predominant facultative anaerobe in the colon normal flora
What are 2 flavors of E. coli?
Pathogenic and nonpathogenic
Can nonpathogenic E coli cause infections?
YES
What are 2 situations in which E. coli causes infections?
-Debilitated or immunosuppressed
-GI barriers breached
What are the 3 clinical syndromes pathogenic E. coli cause?
-UTI
-Sepsis/meningitis
-Enteric diarrhea
How many types of enteric diarrheal diseases do pathogenic E. coli cause?
6
Gram stain morphology of E. coli:
gram neg bacillus
Biochemical id of E. coli:
Glu/Lac fermentor
Gas producer
Indole pos
H2S nonproducer
Is E. coli motile?
Yes
What is a method of identifying different strains of E. coli?
Kauffman serotyping
What are the 4 serotype groups of E. coli?
HOKF
What does HOKF stand for?
H = flagella antigen
O = somatic antigen
K = capsular antigen
F = Fimbrial antigen
What is the O somatic antigen?
LPS - oligosaccharide
What is the K capsular antigen?
Acidic polysaccharide
How many UTIs are caused by E. coli?
90% the majority
What E. coli strain causes UTI?
UPEC - uropathogenic
Where are UPECs normal flora?
In the colon
What are the 3 levels of UTI caused by E. coli?
-Bacteriuria
-Cystitis
-Pyelonephritis
What is the virulence factor that UPEC uses to cause Cystitis?
Type I pili - FimH, an adhesin
What does the FimH type I pili on UPEC bind to?
Uroplakins on the lumenal surface of the bladder.
What virulence factor does UPEC use to cause Pyelonephritis?
P pili
What does the P pili on UPEC bind to to cause pyelonephritis?
Glycolipids on RBCs and Kidney cells
What are Uroplakins? What binds to them again?
Mannose containing cell surface glycoproteins; that's what the FimH type I pili bind to in cystitis.
What type of molecule is FimH?
An adhesin
So the 2 adhesins associated with cystitis are:
-FimH
-Uroplakin
What adhesins area associated with Pyelonephritis?
-P pili (pyeloneph assoc; PAP)
-Glycolipid on RBC/kidney cells
How do UPECs survive the acidic pH and urine flow of the urinary tract?
By residing WITHIN cells
What is the bladder's response to UPEC infection?
Exfoliation
How does a chronic UTI develop?
-overexfoliation=chronic damage
-bacteria survive in pods in the bladder
What is the virulence factor on 80% of E. coli strains causing Neonatal Meningitis?
K1 capsular polysaccharide
What does the capsule contribute to developing neonatal meningitis?
-Resistance to phagocytosis
-Resistance to complement
Where are K1 isolates normally found?
In the colon
Why does K1 cause meningitis?
It has antigenic mimicry with Fetal Neonatal Neuronal tissues.
What is K1 immunologically and chemically identical to?
The capsule polysaccharide of N. meningitidis group B
What is the determining factor for whether E. coli or strep pneumo will cause neonatal meningitis? Which is more virulent?
The magnitude of bacteremia.

Strep pneumo is more virulent - takes fewer bugs to cause it.
What do ALL E.COLI causing diarrhea have at lease one of?
A virulence determinant carried on a plasmid.
How are chromosomal virulence determinants organized?
Into pathogenicity islands - clusters of genes.
What are individual virulence traits encoded on?
-Transposons (ST)
or
-Phage (Stx2)
What are the 3 mechanisms by which E. coli causes diarrhea?
1. Enterotoxin production
2. Intimate adherence and membrane signalling
3. Intracellular invasion
What are the 2 types of Ecoli that have intimate adherence and membrane signalling?
-EPEC - pathogenic
-EHEC - hemorrhagic
What is the Ecoli type that causes intracellular invasion?
EIEC - invasive
What type of diarrhea do you see in ETEC infections?
WATERY with no blood
What are the common cases of ETEC?
-Traveler's diarrhea
-Pediatric diarrhea in developing countries
What is the infectious dose of ETEC?
HIGH
How is ETEC transmitted?
In contaminated food and water
What are the 2 methods of treatment for ETEC?
-Maintain hydration
-Antibiotics may shorten duration
How is ETEC diagnosed?
-Bioassays
-Immunoassay
-Toxin gene probe
Where do the enterotoxigenic E. coli set up colonies?
In the small bowel
What are the toxins expressed by ETEC strains?
-Labile toxin
-Stabile toxin
What is Labile toxin 80% identical to?
Cholera toxin
What is Labile Toxin's structure?
-5 identical B subunits
-1 A subunit
To what cell surface marker are the B subunits specific?
GM1
What happens when labile toxin binds a host enterocyte?
It gets endocytosed, degraded, and A subunit is released into the cytosol.
What is the action of A subunit of stabile toxin?
ADP-ribosylation of Gs
What is Gs?
The stimulatory subunit of adenylate cyclase.
What happens when Gs is ADP-ribosylated?
It activates adenylate cyclase which increases intracellular cAMP
What is the result of increased cAMP?
-CFTR is activated to release Cl which is a diuretic
-NaCl absorption is inhibited
How does the structure of ST compare to LT?
It is a monomer that contains multiple cysteines
What is the result of ST containing multiple cysteines?
It resists heat denaturation
What is ST encoded on?
Plasmids and Transposons
What does ST do?
Binds guanylate cyclase and stimulates cGMP production
What is the result of cGMP production?
CFTR activation, Cl- secretion
So is ST-induced diarrhea distinguishable from LT-induced?
no
Do ETECs only produce ST or LT?
No; some produce both, in which case symptoms are worse.