Flashcards in ID 3 Deck (55):
1
Function of type III secretion system?
facilitates direct delivery of toxins from certain gram negatives to eukaryotic host cells.
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bugs with type III secretion systems?
1) pseudomonas
2) salmonella
3) shigella
4) e coli
3
other name for transformation?
competence
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bugs with transformation ability
1) s pneumo
2) H flu
3) neisseria
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How can you prevent transformation?
add deoxyribonuclease.
6
F+ means?
Has genes required for sex plus and conjugation
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What is transferred through piles in conjugation?
Single strand of plasmid DNA. NO chromosomal DNA.
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Hfr cell?
Cell that has incorporated F+ plasmid into bacterial chromosomal DNA.
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Caveat about Hfr Cells
When plasmid DNA is replicated, some flanking chromosomal DNA can be replaced. Thus, Hfr cells can transfer BOTH plasmid and chromosomal genes.
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transposition occurs?
Between plasmid and chromosome and vice versa
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transposition caveat
flanking chromosomal DNA can be transferred to another bacterium
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example of transposition
vanA gene transferred from VRE to S aureus
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Generalized transduction
A "packaging" event. Lytic phage infects bacterium, leading to cleavage of bacterial DNA. Parts of bacterial chromosomal DNA may become packaged in phage capsid. Phage then infects another bacterium --> genes transferred.
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Specialized transduction
"Excision event." Lysogenic phage infects bacterium; viral DNA incorporates into bacterial chromosome --> phage DNA excised --> flanking bacterial genes may be excised with it --> DNA is packaged into phage capsid and can infect another bacterium.
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Genes from what toxins are encoded in a lysogenic phage?
ABCD's
Group A strep erythrogenic toxin
Botulinum toxin
Cholera toxin
Diphtheria toxin
Shiga toxin
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when do bacteria form spores?
End of stationary phase
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how do you kill spores?
autoclave by steaming at 121 C for 15 minutes.
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Exotoxin composition?
polypeptides
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where are exotoxin genes?
plasmid or bacteriophage
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potency of exotoxins vs. endotoxins
Exotoxins are VERY dangerous (fatal dose on order of 1 microgram)
Endotoxins are less potent (fatal dose on order of hundreds of micrograms)
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antigenicity of exotoxins?
Induces high-titer antibodies called antitoxins.
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what is titer?
way of expressing concentration
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vaccines against exotoxins?
toxoids
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heat stability of exotoxins?
Destroyed rapidly at 60 degrees C (except staphylococcal enterotoxin)
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typical exotoxin diseases
1) tetanus
2) botulism
3) diphtheria
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source of endotoxins?
outer cell membrane of gram negatives
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composition of endotoxins?
Lipid A component of LPS
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Effects of endotoxins?
1) fever
2) shock
3) *DIC
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cytokines induced by endotoxin?
TNF
IL-1
IL-6
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are endotoxins antigenic?
poorly antigenic
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vaccines for endotoxin?
none available
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heat stability of endotoxin?
stable at 100 degrees C for 1 hr
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endotoxin diseases?
1) meningococcemia
2) sepsis by gram negative rods
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Effect of diphtheria toxin?
1) pharyngitis with pseudomembranes in throat
2) severe lymphadenopathy (bull neck)
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name of pseudomonas toxin?
exotoxin A
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shigella toxin
Shiga toxin (ST)
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Shiga toxin mechanism
Inhibits protein synthesis by inactive 60S ribosome by removing adenine from rRNA
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EHEC toxin
Shiva-Like toxin (SLT)
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shiga-like toxin mechanism
inhibits protein synthesis, same as shigella
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What else can shigella cause other than dysentery?
hemolytic-uremic syndrome (HUS) (same toxin)
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difference between shigella and EHEC?
EHEC doesn't invade host cells
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SLT and HUS mechanism?
SLT enhances cytokine release
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Heat-labile toxin (LT) MOA
Over activates adenylate cyclase (increasing cAMP) --> increasing Cl secretion in gut and H2O efflux
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heat-stable toxin (ST) MOA
over activates guanylate cyclase (increasing cGMP) --> decreasing resorption of NaCl and H2O in gut.
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name of anthrax toxin
edema toxin
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MOA of edema toxin?
Mimics adenylate cyclase enzyme, increasing cAMP, and *increasing fluid secretion. This explains the edematous borders of black eschar in cutaneous anthrax.
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cholera toxin MOA
Overactivates adenylate cyclase (increasing cAMP) by permanently activating Gs --> increasing Cl- secretion in gut and H2O efflux.
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Pertussis toxin MOA
Over activates adenylate cyclase (increasing cAMP) by disabling Gi, impairing phagocytosis to permit survival of microbe.
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caveat about whooping cough
toxin may not actually be a cause of cough
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name of tetanus toxin
tetanospasmin
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tetanospasmin and botulinum toxin MOA
proteases that cleave SNARE. **both inhibit release of neurotransmitter.
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What is SNARE?
soluble NSF attachment protein receptor
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cells impaired by tetanus
Renshaw cells (which contain GABA and glycine)
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AB toxins
1) diphtheria
2) exotoxin A of pseudomonas
3) shiga toxin
4) shiga-like toxin
5) Heat-*labile toxin
6) edema toxin
7) cholera toxin
8) pertussis toxin
9) tetanospasmin
10) botulinum
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