What is the causative agent for granuloma inguinale ?

Correct Answer: D. Calymmatobacterium granulomatis

Granuloma inguinale (donovanosis) is caused by Calymmatobacterium granulomatis, a gram-negative, intracellular bacillus. This is a classic STI seen in tropical and subtropical regions, including India, particularly in coastal areas and among lower socioeconomic groups. The organism is identified histologically by Donovan bodies—pathognomonic intracellular inclusions within macrophages and plasma cells seen on tissue biopsy or smear. These appear as rod-shaped, bipolar-staining structures ("safety-pin" appearance) on Wright-Giemsa staining. Clinically, the disease presents as painless, beefy-red, friable ulcers in the genital region with a characteristic "beef-like" granulomatous base. The diagnosis is confirmed by demonstrating Donovan bodies in tissue samples. Unlike syphilis (Treponema) or chlamydial infections, C. granulomatis does not cause systemic manifestations early and is primarily a localized genital ulcer disease. The organism is fastidious and difficult to culture, making histological identification the gold standard. Indian guidelines (NACO/RNTCP) recognize this as a notifiable STI, and treatment typically involves doxycycline or azithromycin for 3 weeks minimum.

Why the other options are wrong

A. Treponema pallidum — This is the causative agent of syphilis, not granuloma inguinale. While both are STIs presenting with genital ulcers, T. pallidum causes a painless, indurated ulcer (chancre) with a clean base and regional lymphadenopathy. Syphilis is systemic and progresses through stages; granuloma inguinale remains localized. This is a common NBE trap pairing STIs with ulcers. B. Chlamydia trachomatis — C. trachomatis causes lymphogranuloma venereum (LGV), another STI with genital ulcers, but the clinical presentation differs markedly. LGV presents with a small transient ulcer followed by severe, painful inguinal lymphadenopathy (buboes). Chlamydia is also the leading cause of cervicitis and PID in India. The absence of Donovan bodies rules out C. trachomatis. C. Ureaplasma urealyticum — U. urealyticum is a mycoplasma associated with non-gonococcal urethritis (NGU) and occasionally PID, not genital ulcer disease. It does not produce granulomatous lesions or Donovan bodies. This option exploits confusion between different STI pathogens and their clinical presentations.

High-Yield Facts

Mnemonics

STI Ulcer Agents (TCCG) Treponema (syphilis, chancre), Chlamydia (LGV, buboes), Calymmatobacterium (granuloma inguinale, Donovan bodies), Gonorrhea (urethritis, not ulcer). Use when differentiating genital ulcer STIs. Donovan Bodies = Granuloma Inguinale Donovan bodies → Donovanosis (granuloma inguinale). Pathognomonic finding; if you see Donovan bodies on exam, answer is C. granulomatis.

NBE Trap

NBE commonly pairs all STIs causing genital ulcers (syphilis, LGV, granuloma inguinale) in a single question to test whether students can discriminate by organism, histology (Donovan bodies), and clinical presentation (painless friable ulcer vs. indurated chancre vs. buboes).

Clinical Pearl

In Indian clinical practice, granuloma inguinale is often underdiagnosed because it mimics other STIs; the key bedside clue is the beefy-red, painless ulcer with a granulomatous base and absence of severe lymphadenopathy. Tissue biopsy showing Donovan bodies clinches the diagnosis and guides treatment with doxycycline, preventing complications like secondary infection and scarring.

_Reference: Jawetz Melnick & Adelberg's Medical Microbiology Ch. 27 (Spirochetes & Atypical Bacteria); Park's Textbook of Preventive & Social Medicine Ch. 6 (STIs)_