A neutropenic patient post-allogenic stem cell transplant develops fever unresponsive to broad-spectrum antibiotics. CT thorax shows multiple nodules with a 'halo sign.' Serum galactomannan (ELISA) is ordered. The galactomannan assay detects a component of the cell wall of:
- A Candida species — β(1→3)-D-glucan released during candidal invasion
- B Aspergillus species — β(1→5)-linked galactofuranose side chains on the galactomannan polysaccharide ✓
- C Cryptococcus neoformans — glucuronoxylomannan capsular polysaccharide
- D Mucor/Rhizopus species — chitin degradation products released during hyphal growth
Explanation
Galactomannan (GM) is a polysaccharide component of the Aspergillus cell wall consisting of a mannan backbone with galactofuranose (Galf) side chains. It is released during active hyphal growth. The Platelia Aspergillus ELISA detects GM in serum and BAL using rat monoclonal antibody EB-A2. In hematological malignancy and HSCT patients, serum GM optical density index (ODI) ≥0.5 (or ≥1.0 in some guidelines) is the cut-off for positivity. BAL GM ≥1.0 is more sensitive for pulmonary aspergillosis. Importantly, GM can also be positive in other mold infections (Fusarium, Histoplasma) and with piperacillin-tazobactam. (1→3)-β-D-glucan (BDG) is broader — detects Aspergillus, Candida, PCP, Fusarium but NOT Cryptococcus or Mucorales.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.