**Core Concept**
Granulomatous infantisepticum is a rare, life-threatening condition characterized by the formation of granulomas in the skin and internal organs of newborns. It is a form of congenital histiocytosis caused by an abnormal accumulation of histiocytes, leading to tissue damage and inflammation.

**Why the Correct Answer is Right**
The correct answer is **B. Histoplasma capsulatum**. Granulomatous infantisepticum is caused by an intrauterine infection with Histoplasma capsulatum, a dimorphic fungus that typically affects the lungs of adults. The fungus can be transmitted to the fetus through the placenta, leading to the development of granulomatous lesions. The pathogenesis involves the activation of histiocytes, which form granulomas in an attempt to contain the fungal infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Granulomatous infantisepticum is not caused by a bacterial infection. While bacterial infections can cause granulomatous reactions, the specific condition described in the question is due to a fungal infection.

**Option C:** This option is incorrect because Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis, a different congenital infection that can affect the central nervous system and eyes of newborns.

**Clinical Pearl / High-Yield Fact**
Toxoplasmosis and granulomatous infantisepticum are both congenital infections that can be prevented with antenatal screening and treatment. However, granulomatous infantisepticum is a rare and often fatal condition that requires prompt diagnosis and treatment to improve outcomes.

**Correct Answer: B. Histoplasma capsulatum**