This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Haemophilus, Yersinia, Spirochaetes, Ricketssia, Chlamydia, Mycoplasma and Miscellaneous Bacteria), Subject name: Microbiology
Mechanism of action of cholera toxin is through: 
Select and explain. 
A. Gangliosides, B. Adenyl cyclase, C. Gangliosides + adenyl cyclase, D. Exotoxin
C: Gangliosides + adenyl cyclase
Answer: C: Gangliosides + adenyl cyclase 
Explanation: Cholera enterotoxin Light toxin: binds with ganglioside in epithelial cell membrane Heavy toxin: activates adenyl cyclase in epithelial cell wall which increase cAMP, leading to outpouring of isotonic fluid in lumen of intestine