Erythrasma: The Causative Agent Explained

Erythrasma is a superficial bacterial skin infection that affects the outermost layer of the skin, the epidermis, specifically the stratum corneum. It typically presents as reddish-brown, slightly scaly patches, often found in skin folds like the groin, armpits, and between the toes. The question asks for the specific bacterium responsible for this condition.

Understanding Corynebacterium minutissimum

The causative agent of Erythrasma is identified as Corynebacterium minutissimum. This bacterium is a normal inhabitant of the skin but can overgrow under certain conditions, leading to the infection known as Erythrasma.

• Corynebacterium minutissimum produces porphyrins, specifically coproporphyrin III.
• These porphyrins cause the characteristic coral-red fluorescence observed when the affected skin is viewed under a Wood's lamp (an ultraviolet light). This is a key diagnostic feature.
• The infection is generally mild and asymptomatic, but can sometimes cause itching or discomfort.

Distinguishing Other Corynebacterium Species

The other options provided are also species within the *Corynebacterium* genus, but they are not the cause of Erythrasma:

• Corynebacterium pseudotuberculosis: This bacterium is primarily known to cause infections in animals (like caseous lymphadenitis in sheep and goats) and occasionally zoonotic infections in humans, often related to contact with animals or contaminated animal products. It does not cause Erythrasma.
• Corynebacterium diphtheriae: This is the well-known bacterium that causes diphtheria, a serious infectious disease affecting the throat (pharynx) and upper respiratory tract, characterized by the formation of a pseudomembrane. It is not associated with skin infections like Erythrasma.
• Corynebacterium matruchotii: This species is typically found as a commensal organism in the human oral cavity (mouth) and is associated with dental plaque and calculus. It is not implicated in Erythrasma.

Diagnostic Features of Erythrasma

Key points to remember about Erythrasma include:

• It's a superficial infection of the stratum corneum.
• It is caused by Corynebacterium minutissimum.
• Characteristic coral-red fluorescence under Wood's lamp.
• Commonly affects intertriginous areas (skin folds).
• Treatment often involves topical or oral antibiotics like erythromycin or tetracyclines.

Therefore, Corynebacterium minutissimum is the correct answer as the specific causative agent of Erythrasma.