## **Core Concept**
Salmonella species are gram-negative, rod-shaped bacteria known for their motility, which is primarily facilitated by peritrichous flagella. However, there are exceptions within the Salmonella genus regarding their motility characteristics.

## **Why the Correct Answer is Right**
The correct answer, , is notable because it represents *Salmonella Typhi*, a strain that is typically non-motile or possesses a very limited form of motility, and when present, the flagella are not peritrichous but rather polar or lateral in some descriptions, but generally considered to lack typical peritrichous flagella seen in other Salmonella species. This characteristic differentiates *S. Typhi* from other Salmonella species like *Salmonella Typhimurium* and *Salmonella Enteritidis*, which exhibit motility via peritrichous flagella.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option represents a motile strain of Salmonella, implying the presence of peritrichous flagella, which is typical for many Salmonella species.
- **Option B:** Similar to option A, this strain is also motile by peritrichous flagella, aligning with the common characteristics of many Salmonella species.
- **Option D:** This option also exhibits motility via peritrichous flagella, which is a feature commonly associated with Salmonella.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that *Salmonella Typhi* is an exception among Salmonella species due to its non-motility or atypical motility, which can be an important distinguishing feature in laboratory identification.

## **Correct Answer: .**