A farmer presents with a lesion that discharges black-colored granules. What is the causative agent?

INI-CET EXAM -2025

Applied Microbiology & Infection control

Easy

Appeared in: INI-CET EXAM -2025

Explanation

The clinical condition described is mycetoma (also known as Madura foot), a chronic granulomatous infection of the skin and subcutaneous tissues.
A key diagnostic feature of mycetoma is the presence of granules (grains) in the discharge from sinus tracts.
The color of these granules helps identify the causative agent. Black or dark-brown granules are pathognomonic for eumycetoma caused by the fungus Madurella mycetomatis.
This organism is a common soil saprophyte, and infection often occurs after traumatic inoculation, which is a common occupational hazard for farmers.

Option B: Actinomadura madurae is a cause of actinomycetoma, which is a bacterial infection. It characteristically produces white to yellow colored granules, not black.
Option C: Nocardia brasiliensis is another bacterial cause of actinomycetoma. It typically produces small, white to yellow granules.
Option D: Streptomyces somaliensis is a bacterial agent causing actinomycetoma. It is known to produce larger, hard, yellow to brown granules, but not black.

Visual 1: Clinical Photograph - An image of a 'Madura foot' showing the characteristic swelling, multiple sinus tracts, and the discharge of black granules. This helps in visualizing the classic presentation of eumycetoma.
Visual 2: Micrograph - A microscopic image of a crushed black granule in a KOH mount, revealing the septate, pigmented fungal hyphae of Madurella mycetomatis. This confirms the fungal etiology.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Etiology of Mycetoma (Madura Foot) as background academic context rather than a clinical decision trigger.
Identifying the granule color is a critical first step in managing mycetoma, as the treatment differs significantly between fungal (eumycetoma) and bacterial (actinomycetoma) causes.
Eumycetoma requires long-term antifungal therapy (e.g., itraconazole, voriconazole) often combined with surgical debridement, while actinomycetoma responds to prolonged courses of antibiotics (e.g., co-trimoxazole and amikacin).
Patient education is crucial, especially for high-risk individuals like farmers. Emphasizing the use of protective footwear can significantly reduce the incidence of this debilitating infection.

How to Approach the Question

First, identify the key clinical features presented in the question: a lesion with discharging granules and the patient's occupation (farmer).
Focus on the most specific detail: the 'black color' of the granules. This is a classic diagnostic sign in microbiology.
Recall or deduce that this presentation is characteristic of mycetoma (Madura foot).
Link the color of the granules to the type of mycetoma. Black granules indicate eumycetoma (fungal), while white/yellow granules suggest actinomycetoma (bacterial).
Evaluate the options provided. Madurella mycetomatis is a fungus known to cause black-grain mycetoma. The other options are bacteria that cause different colored granules.
Select the option that matches the specific finding of black granules.

Concept Tested & Keywords

Concept Tested: Etiology of Mycetoma (Madura Foot)
Stem keywords: lesion, black-colored granules, farmer
Lead-in keywords: causative agent
Clinical cues: The presence of 'black-colored granules' is the most specific clinical clue, pointing directly to a particular type of mycetoma.

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