L47 Flashcards
E.Coli: GN or GP Shape Air status Grow on MacConkey agar? Ferment lactose? Where part of normal flora Motile?
GN rod - typical of GI flora Facultative anaerobe YES grows on MacConkey YES ferments lactose Motile w/ flagella
What the 2 characteristics that E.Coli are serotyped on?
O antigen = repeating polysaccharides @ end of LPS
H antigen = flagellar antigen (highly variable)
What is the serotype of the most common pathogenic strain of E.Coli?
O157:H7
How can E.coli both be normal GI flora AND cause so many diseases?
Virulence factors on:
Plasmids
Bacteriophages
PIs
What is ETEC? What are the clinical features/picture?
ETEC = entero-toxigenic E.Coli WATERY diarrhea (short) *Developing countries - children + travelers
How is ETEC transmitted?
Fecal-oral
Need high inoculum for disease
What are the virulence factors for ETEC?
Plasmid w/:
1. Colonization factor = pili for GI adhesion, unique to each strain!!
2. Heat labile enterotoxin (aka destroyed by heat)
3. Heat stable enterotoxin
Aka secreting enterotoxin at pretty much any temp
How do you gain immunity against ETEC?
Immunity vs pili (colonization factor)
But b/c this variability changes with each stain, immunity is UNLIKELY
Explain how heat-labile enterotoxin works.
B subunit uptake into GI cells
Retrograde transport to golgi
A subunit is ejected and moves to the BL surface of the cell
A ADP ribosylates Gs –> activates adenylate cyclase
Increased cAMP production
Turn on PKA –> open CFTR = open Cl- channel
Na blocked + Cl moving from cells into lumen = NaCl in lumen
H2O follows
WATERY diarrhea
Explain the heat-stable enterotoxin mechanism.
Elevated cGMP (this is the difference!!) Same down stream effects
Treat ETEC (traveler’s diarrhea).
Oral rehydration
Antimicrobial to shorten duration only:
- Fluoro +/- antimotility agent
- Non-absorbable rifaximin
What is EPEC? What are the clinical symptoms/picture?
EPEC - entero-pathogeneic E.Coli Watery diarrhea + vomiting!! (Problematic for oral rehydration) Infants - only - @ developing countries Can be DEADLY!
How is EPEC transmitted?
Person-person
What is EPEC’s disease mechanism/virulence factors?
Both REQUIRED for VIRULENCE
Adherence - pili,
- On plasmid
- Bacteria aggregate in microcolonies
T3SS - modifies cytoskeleton for attachment
- On PI
- Intimin (bacterial ligand)/tir (host receptor)
What is tir?
Translocated intimin receptor
In the host (target) cell
Binds intimin –> actin polyermization
Net = pedestal for bacterial attachment to gut (vs normal pili)
How do you treat/prevent EPEC?
Prevent: babies drink breast milk!
Treat: oral/IV rehydration
What is EHEC? What is the reservoir? Transmission?
Entero-hemorrhagic E.Coli Reservoir = cattle (petting zoos) Transmitted: - Contaminated beef, spinach, water - Unpasteurized juice - Person-person (low inoculum)
Which toxin does EHEC secrete? How did it get this virulence factor?
Shiga toxin From bacteriophages B + A subunits Retrograde transport to ER Depurinates 28S ribosome subunit X protein synthesis Cell DIES --> initiates CLOTTING
What triggers EHEC shiga toxin production?
Body’s SOS signals
- Antibiotics
- Oxidative stress
Otherwise laying latent in lysogenic phase of bacteriophage
- SOS turns on late genes –> into lytic
TAKE HOME = antibiotics may be associated with higher complication rates
How did EHEC evolve?
EPEC + bacteriophage w/ Shiga toxin = EHEC
What is EHEC’s other main virulence factor?
Attaching & effacing
Describe the clinical progression/presentation of EHEC.
Cramps/pain
Watery –> bloody diarrhea
Progression = HUS
What is HUS?
Hemolytic uremic syndrome
Clots in capillaries (thrombocytopenia) + hemolysis as RBCs lysed
Increased risk w/ ANTIBIOTICS
Brought on by EHEC - could cause permanent kidney damage
How do you diagnose EHEC?
- MacConkey agar
- Non-O125H7 stains = most = ferment sorbitol - ELISA for Shiga toxin
NEED BOTH
What is EAEC? Describe the clinical symptoms/presentation.
Entero-aggregative E.Coli
Kids w/ growth retardation
Traveler’s diarrhea
HIV patients
What are the virulence factors for EAEC?
Adhesion = fimbrae (plasmid) Damages intestinal cells Toxins: - Pet - EAST
What are the pathogenic mechanisms by which E.Coli can cause neonatal meningitis?
K1 capsule
Fimbriae
Invasiveness - crosses BBB
Klebsiella encapsulated?
YES & mucoid
Infections caused by Klebsiella
UTI
Severe pneumonia
Nosocomial infections
Which drugs is Klebsiella resistant to?
ALWAYS resistant to penicillins
Enterobacter and serratia encapsulated?
YES & mucoid
What infections do enterobacter and serratia cause?
NOSOCOMIAL infections
What drug is easily induced to be resistant in enterobacter and serratia?
Cephalosporins - don’t use them!! Even if report says susceptible
What are 4 virulence factors of proteus?
- Urease + (makes urine alkaline)
- Swarming motility
- Fimbriae
- Hemolysin
Which drugs are proteus resistant to?
Tigecycline & polymixin
How do you treat P.mirabilis?
Same way you'd treat E.Coli Ampicillin TMPX-SMX Cephalo Fluoro
How do you treat P.vulgaris?
More likely to be resistant, so…
3rd gen cephalo
Fluoro
