Q: Which of the following equations correctly represents the ADP-ribosylation reaction catalyzed by diphtheria toxin?

$$\mathrm{NAD^+ + EF2 \rightarrow ADP\text{-}ribosyl\text{-}EF2 + Nicotinamide}$$

Question 1

Which component of the Gram-negative bacterial outer membrane is responsible for the toxic effects associated with endotoxemia and septic shock?

Accepted Answer

Lipid A

Question 2

A patient presents with a painless, necrotic skin ulcer that is relatively free of inflammation and other microbes. Which bacterial toxin is most likely responsible for this presentation?

Accepted Answer

Mycolactone

Question 3

Which of the following best describes the mechanism of action of diphtheria toxin?

Accepted Answer

It ADP-ribosylates elongation factor 2 (EF2), inhibiting protein synthesis.

Question 4

Which of the following equations correctly represents the ADP-ribosylation reaction catalyzed by diphtheria toxin?

Accepted Answer

$$\mathrm{NAD^+ + EF2 ightarrow ADP	ext{-}ribosyl	ext{-}EF2 + Nicotinamide}$$

Question 5

A laboratory test shows a clear zone around a bacterial colony on blood agar. Which type of hemolysis and toxin is most likely responsible?

Accepted Answer

Beta-hemolysis; hemolysin

Question 6

Which of the following best explains why superantigens can cause toxic shock syndrome?

Accepted Answer

They nonspecifically activate a large proportion of T cells, causing a cytokine storm.

Question 7

Which secretion system is used by Salmonella enterica to inject toxic effector proteins directly into host cells?

Accepted Answer

Type III secretion system (T3SS)

Question 8

A new hybrid AB toxin is discovered with an A part similar to diphtheria toxin and a B part similar to botulinum toxin. What is the most likely effect of this toxin on nerve cells?

Accepted Answer

It will kill the cells by inhibiting protein synthesis.

Question 9

Which of the following is a distinguishing feature of mycolactones compared to other bacterial toxins?

Accepted Answer

They are polyketide-derived macrolides with immunosuppressive properties.

Question 10

Which of the following best describes the function of the B subunit in AB-type toxins?

Accepted Answer

It binds to host cell receptors and mediates entry of the toxin.

Question 11

Which of the following is a direct effect of the action of botulinum neurotoxin at the neuromuscular junction?

Accepted Answer

Inhibition of synaptic vesicle fusion, leading to flaccid paralysis

Question 12

Which of the following best explains why Listeria monocytogenes can spread rapidly from cell to cell without exposure to the humoral immune system?

Accepted Answer

It uses actin-based motility to move directly between host cells.

Question 13

Which of the following is a characteristic of endotoxins but NOT exotoxins?

Accepted Answer

They are components of the bacterial outer membrane released upon cell lysis.

Question 14

Which of the following best describes the role of the Type VI secretion system (T6SS) in bacteria such as Vibrio cholerae?

Accepted Answer

It transfers bacterial proteins from one bacterium to another.

Question 15

Which of the following best explains the formation of a pseudomembrane in diphtheria infection?

Accepted Answer

Accumulation of dead mucosal cells, bacteria, and inflammatory cells due to diphtheria toxin action

Question 16

Which of the following is a common feature of all AB-type toxins?

Accepted Answer

They have separate domains for binding and enzymatic activity.

Question 17

Which of the following best describes the effect of tracheal cytotoxin (TCT) in Bordetella pertussis infection?

Accepted Answer

It causes loss of ciliated cells, leading to persistent coughing.

Question 18

Which of the following best explains why some bacterial toxins are classified as superantigens?

Accepted Answer

They bind to MHC class II and TCR outside the normal antigen-binding site, activating many T cells.

Question 19

Which of the following is a likely outcome if a patient is exposed to high levels of endotoxin in the bloodstream?

Accepted Answer

Septic shock due to overstimulation of cytokine signaling

lecture 13

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