Aspergillus fumigatus causes invasive aspergillosis in profoundly neutropenic patients. Galactomannan ELISA on serum is used for early diagnosis. What is the structural basis of galactomannan antigenicity and which other fungus can cause false-positive results?

• A Beta-glucan component of cell wall; false positives from Candida
• B Ergosterol in fungal membrane; false positives from Cryptococcus
• C Galactofuranose-containing polysaccharide released from Aspergillus cell wall during growth; Histoplasma capsulatum cross-reacts causing false positives ✓
• D Chitin in cell wall; false positives from Mucor

Explanation

Galactomannan is a polysaccharide component of the Aspergillus cell wall containing galactofuranose side chains, which are released during active hyphal growth. The Platelia Aspergillus ELISA detects galactomannan antigenemia in serum or BAL fluid. Cross-reactivity occurs with Histoplasma capsulatum, Penicillium/Talaromyces marneffei, and some bacteria (Bifidobacterium). The (1,3)-β-D-glucan assay is broader (panfungal) and does not detect Cryptococcus or Mucorales. Galactomannan index (ODI) ≥0.5 in serum is considered positive per EORTC criteria.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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