True about cholera vibrios is –
**Core Concept**
Cholera vibrios, specifically Vibrio cholerae, are a type of Gram-negative, facultative anaerobic bacteria that cause cholera, a diarrheal disease characterized by profuse watery stools. The bacteria possess a unique virulence factor, the cholera toxin, which plays a crucial role in the pathogenesis of the disease.
**Why the Correct Answer is Right**
The cholera toxin, composed of two subunits (A and B), is secreted by Vibrio cholerae into the intestinal lumen, where it binds to the intestinal epithelial cells. The B subunit of the toxin binds to the GM1 ganglioside receptors on the intestinal epithelial cells, while the A subunit enters the cell and activates the adenylate cyclase enzyme, leading to an increase in intracellular cAMP levels. This results in the activation of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels, causing an influx of chloride ions into the intestinal lumen and resulting in the characteristic profuse watery diarrhea.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect as it does not provide any relevant information about cholera vibrios.
**Option B:** This option might be incorrect as it does not accurately describe the mechanism of action of the cholera toxin.
**Option C:** This option is incorrect as it does not provide any relevant information about cholera vibrios.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that Vibrio cholerae can survive for several weeks in contaminated water and food, making it a significant public health concern in areas with poor sanitation and hygiene.
**Correct Answer: D.**