Question

The pathogenesis of Vibrio cholerae is due to the organism's ability to produce cholera toxin. This is an A-B toxin that affects host cells in the small intestine. Which of the following correctly describes the mechanism of the toxin?

a. The "A" subunit binds to host cell receptors while the "B" subunit causes enzymatic activity.
b. The "B" subunit binds to host cell receptors while the "A" subunit causes uncontrolled secretion of ions and water.
c. The "A" subunit causes enzymatic activity while the "B" subunit enters the host cell.
d. The "B" subunit causes uncontrolled secretion of ions and water while the "A" subunit binds to host cell receptors.

Answer 1

The B subunit of cholera toxin binds to host cell receptors, and the A subunit activates adenyl cyclase causing secretion of ions and water, leading to diarrhea.

Step-by-step explanation:

The pathogenesis of Vibrio cholerae is due to the organism's ability to produce cholera toxin, which is an A-B toxin that affects host cells in the small intestine. The correct mechanism of the toxin is that the 'B' subunit binds to host cell receptors while the 'A' subunit enters the host cell and causes uncontrolled secretion of ions and water. Specifically, the B subunits bind to receptors on the intestinal epithelial cells, and once inside, the A subunit activates an intracellular G protein which then leads to the activation of the enzyme adenyl cyclase. This enzyme produces an increase in cyclic AMP (cAMP), which causes the intestinal epithelial cells to secrete large amounts of fluid and electrolytes into the intestinal tract, resulting in severe diarrhea.