A patient with uncontrolled diabetes mellitus presents with acute rhinosinusitis with black eschar on the hard palate and periorbital oedema. MRI shows invasion of the orbital apex and cavernous sinus. The organism most likely to be isolated on Sabouraud medium is:

• A Aspergillus fumigatus with septate hyphae at 45-degree angles
• B Mucor species with broad aseptate hyphae without rhizoids
• C Candida tropicalis with pseudohyphae and blastoconidia
• D Rhizopus arrhizus (oryzae) with broad aseptate hyphae and rhizoids at the node ✓

Explanation

The clinical scenario describes rhinoorbital-cerebral mucormycosis in a diabetic patient — the most common form of mucormycosis. Rhizopus arrhizus (synonymous with R. oryzae) is the most common causative species of mucormycosis globally. On culture and direct microscopy, Mucorales show characteristic broad (6–25 µm), aseptate (or sparsely septate) ribbon-like hyphae; Rhizopus specifically produces rhizoids (root-like structures at nodes where stolons arise), distinguishing it from Mucor (no rhizoids). Aspergillus has narrow, septate hyphae with 45-degree angle branching. Accurate species identification guides isavuconazole vs. amphotericin B choice.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.