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?

Calymmatobacterium granulomatis is a gram-negative rod that causes granuloma inguinale (also known as donovanosis), a sexually transmitted disease characterized by genital ulceration and soft tissue and bone destruction. The diagnosis is made by visualizing the stained organisms (Donovan bodies) within large macrophages from the lesion. Tetracycline is the treatment of choice for this disease, which is rare in the United States but endemic in many developing countries. C. granulomatis is also known as Klebsiella granulomatis. Ref: Levinson W. (2012). Chapter 27. Minor Bacterial Pathogens. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.