Beta-D-glucan (BDG) assay is used as a pan-fungal biomarker. Which organisms produce a FALSE-NEGATIVE BDG result despite causing invasive fungal infection?

• A Mucorales (Rhizopus, Mucor) and Cryptococcus neoformans ✓
• B Aspergillus species and Candida species
• C Pneumocystis jirovecii and Talaromyces marneffei
• D Fusarium and Trichosporon species

Explanation

Beta-D-glucan (1,3-BDG) is a cell wall polysaccharide component of most fungi and is detectable in serum during invasive fungal infection. However, Mucorales (Zygomycetes such as Rhizopus, Mucor, Lichtheimia) have cell walls that are enriched in chitin and glucan in a form that is not released systemically in detectable amounts — hence BDG is consistently negative in mucormycosis. Cryptococcus neoformans is encapsulated and the polysaccharide capsule is predominantly glucuronoxylomannan, which does not cross-react with the BDG assay. Aspergillus, Candida, PCP (P. jirovecii), Fusarium, and Trichosporon all give positive BDG results.

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

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