A 26 year male patient presented with a granulomatous penile ulcer. On Wright Giemsa staining, tiny organisms of 2 microns are seen engulfed by macrophages. What is the causative organism?
**Core Concept**
The patient's presentation of a granulomatous penile ulcer with tiny organisms engulfed by macrophages on Wright Giemsa staining is suggestive of a sexually transmitted infection caused by an intracellular bacterium. This organism is known to cause a chronic infection that leads to the formation of granulomas, which are characteristic of the body's immune response to this pathogen.
**Why the Correct Answer is Right**
The causative organism is *Haemophilus ducreyi*, but that is not present in this description. The description points towards *Calymmatobacterium granulomatis*, previously known as Klebsiella granulomatis. This bacterium is an obligate intracellular pathogen that causes Donovanosis, also known as Granuloma Inguinale. The organisms are engulfed by macrophages, which are then seen on Wright Giemsa staining as tiny blue-purple inclusions, known as Donovan bodies.
**Why Each Wrong Option is Incorrect**
* **Option A:** *Haemophilus ducreyi*, the causative organism of chancroid, typically presents with painful ulcers and is not associated with Donovan bodies on Wright Giemsa staining.
* **Option B:** *Treponema pallidum*, the causative organism of syphilis, typically presents with a painless chancre and is not associated with Donovan bodies on Wright Giemsa staining.
* **Option C:** *Neisseria gonorrhoeae*, the causative organism of gonorrhea, typically presents with a painful urethritis and is not associated with Donovan bodies on Wright Giemsa staining.
**Clinical Pearl / High-Yield Fact**
Donovanosis, caused by *Calymmatobacterium granulomatis*, is a sexually transmitted infection that typically presents with granulomatous ulcers, especially in tropical regions. It is often misdiagnosed as other sexually transmitted infections, such as chancroid or syphilis.
**Correct Answer:** C. *Calymmatobacterium granulomatis*.