Infective dose of salmonella typhi –
**Core Concept**
The infective dose of Salmonella Typhi refers to the number of bacteria required to initiate an infection in a susceptible host. Salmonella Typhi is a Gram-negative bacterium that causes typhoid fever, a serious and potentially life-threatening disease.
**Why the Correct Answer is Right**
The infective dose of Salmonella Typhi is estimated to be as low as 10-100 bacteria. This is because S. Typhi has a unique ability to invade and replicate within the intestinal epithelial cells, allowing it to evade the host's immune system. The bacteria can then spread to other parts of the body, including the bloodstream, lymph nodes, and spleen, causing systemic infection.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the actual infective dose is much lower than 10,000 bacteria.
* **Option B:** This option does not provide a specific number, making it an unclear choice.
* **Option C:** This option is incorrect because the exact number of bacteria required for infection is not 100,000.
* **Option D:** This option does not provide a specific number, making it an unclear choice.
**Clinical Pearl / High-Yield Fact**
The infective dose of S. Typhi is often referred to as the "low dose-high yield" phenomenon, highlighting the bacteria's ability to cause disease with a relatively small number of organisms.
**Correct Answer: D. 10-100**