ID 3 Flashcards by Ned Jones

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

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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.

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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

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