ID 3 Flashcards
Function of type III secretion system?
facilitates direct delivery of toxins from certain gram negatives to eukaryotic host cells.
bugs with type III secretion systems?
1) pseudomonas
2) salmonella
3) shigella
4) e coli
other name for transformation?
competence
bugs with transformation ability
1) s pneumo
2) H flu
3) neisseria
How can you prevent transformation?
add deoxyribonuclease.
F+ means?
Has genes required for sex plus and conjugation
What is transferred through piles in conjugation?
Single strand of plasmid DNA. NO chromosomal DNA.
Hfr cell?
Cell that has incorporated F+ plasmid into bacterial chromosomal DNA.
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.
transposition occurs?
Between plasmid and chromosome and vice versa
transposition caveat
flanking chromosomal DNA can be transferred to another bacterium
example of transposition
vanA gene transferred from VRE to S aureus
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.
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.
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
when do bacteria form spores?
End of stationary phase
how do you kill spores?
autoclave by steaming at 121 C for 15 minutes.
Exotoxin composition?
polypeptides
where are exotoxin genes?
plasmid or bacteriophage
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)
antigenicity of exotoxins?
Induces high-titer antibodies called antitoxins.
what is titer?
way of expressing concentration
vaccines against exotoxins?
toxoids
heat stability of exotoxins?
Destroyed rapidly at 60 degrees C (except staphylococcal enterotoxin)
typical exotoxin diseases
1) tetanus
2) botulism
3) diphtheria
source of endotoxins?
outer cell membrane of gram negatives
composition of endotoxins?
Lipid A component of LPS
Effects of endotoxins?
1) fever
2) shock
3) *DIC
cytokines induced by endotoxin?
TNF
IL-1
IL-6
are endotoxins antigenic?
poorly antigenic
vaccines for endotoxin?
none available
heat stability of endotoxin?
stable at 100 degrees C for 1 hr
endotoxin diseases?
1) meningococcemia
2) sepsis by gram negative rods
Effect of diphtheria toxin?
1) pharyngitis with pseudomembranes in throat
2) severe lymphadenopathy (bull neck)
name of pseudomonas toxin?
exotoxin A
shigella toxin
Shiga toxin (ST)
Shiga toxin mechanism
Inhibits protein synthesis by inactive 60S ribosome by removing adenine from rRNA
EHEC toxin
Shiva-Like toxin (SLT)
shiga-like toxin mechanism
inhibits protein synthesis, same as shigella
What else can shigella cause other than dysentery?
hemolytic-uremic syndrome (HUS) (same toxin)
difference between shigella and EHEC?
EHEC doesn’t invade host cells
SLT and HUS mechanism?
SLT enhances cytokine release
Heat-labile toxin (LT) MOA
Over activates adenylate cyclase (increasing cAMP) –> increasing Cl secretion in gut and H2O efflux
heat-stable toxin (ST) MOA
over activates guanylate cyclase (increasing cGMP) –> decreasing resorption of NaCl and H2O in gut.
name of anthrax toxin
edema toxin
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.
cholera toxin MOA
Overactivates adenylate cyclase (increasing cAMP) by permanently activating Gs –> increasing Cl- secretion in gut and H2O efflux.
Pertussis toxin MOA
Over activates adenylate cyclase (increasing cAMP) by disabling Gi, impairing phagocytosis to permit survival of microbe.
caveat about whooping cough
toxin may not actually be a cause of cough
name of tetanus toxin
tetanospasmin
tetanospasmin and botulinum toxin MOA
proteases that cleave SNARE. **both inhibit release of neurotransmitter.
What is SNARE?
soluble NSF attachment protein receptor
cells impaired by tetanus
Renshaw cells (which contain GABA and glycine)
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
AB toxin structure
B enables binding, A is usually ribosyltransferases
