**Question:** True about T. pallidum is -

A. Treponema pallidum is a non-motile bacterium
B. T. pallidum is resistant to most antibiotics
C. T. pallidum is the causative agent of syphilis
D. T. pallidum is a slow-growing bacterium

**Correct Answer:**

**Core Concept:** Treponema pallidum is a spirochete bacterium responsible for causing syphilis, a sexually transmitted disease. It belongs to the family Spirocheteaceae and is characterized by its unique spiral shape, which allows it to move through tissues and resist phagocytosis.

**Why the Correct Answer is Right:** T. pallidum is a non-motile bacterium due to its spiral shape, which allows it to move through tissues by twisting and bending, rather than the conventional "whip-like" movement of other bacteria. This distinctive characteristic helps the bacterium evade the immune system and establish infection in the host.

**Why Each Wrong Option is Incorrect:**

A. T. pallidum is motile due to its unique spiral shape, not non-motile as stated in this option.
B. Although T. pallidum has developed resistance to some antibiotics, it is not resistant to all of them. Many antibiotics can successfully treat syphilis when administered correctly and in appropriate dosages.
C. This option represents the correct answer, as T. pallidum is indeed the causative agent of syphilis.
D. Contrary to this option, T. pallidum is a fast-growing bacterium compared to other slow-growing pathogens. It has a rapid growth rate and can be cultured in laboratory conditions within 2-4 weeks, allowing for diagnosis and treatment.

**Clinical Pearl:** Syphilis caused by T. pallidum is a significant public health concern, especially in the context of HIV-infected individuals, as syphilis can complicate HIV infection and worsen the clinical outcome. Early diagnosis and appropriate antibiotic treatment are crucial in preventing severe complications and long-term health consequences.