Granuloma inguinale is caused by which organism?

• A. Chlamydia trachomatis
• B. Calymmatobacterium granulomatis
• C. Neisseria gonorrhoeae
• D. Haemophilus ducreyi

Answer: (D)

Granuloma inguinale is caused by a gram-negative bacillus that lives inside macrophages in tissue. This organism, historically called Calymmatobacterium granulomatis and now reclassified as Klebsiella granulomatis, produces intracellular inclusions known as Donovan bodies that you can identify in tissue smears or biopsies—these are a key diagnostic clue. Clinically, the ulcers of granuloma inguinale are typically painless, progressive, and bleed easily, with little or no lymph node involvement, which helps distinguish it from other genital ulcers. Haemophilus ducreyi causes chancroid, which presents with painful ulcers and tender inguinal nodes; Neisseria gonorrhoeae causes gonorrhea; Chlamydia trachomatis can cause lymphogranuloma venereum or nongonococcal urethritis. The organism that best fits granuloma inguinale’s histology and clinical picture is Calymmatobacterium granulomatis (Klebsiella granulomatis).