Correct Answer
2. Aspergillus terreus
The fungus was identified via MALDI-TOF MS as Aspergillus terreus.
Microscopy Findings
The culture revealed thin, hyaline hyphae with parallel walls, 4–6 μm in diameter, with septations and acute-angle branching at 45°, consistent with hyaline hyphomycetes. This contrasts with mucormycetes, which are characterized by broader, irregular hyphae with thin walls, sparse or absent septations, and broader branching angles (45°–90°), resembling ribbons. The defining feature of A. terreus, a double row of phialides, was not distinctly observed in the direct preparation.
Colony Appearance
The colony coloration was consistent with A. terreus (brownish colonies). Comparatively: A. niger: black, pepper-like colonies, A. fumigatus: dark green colonies, A. flavus: yellow-green colonies.
Antifungal Resistance
A. terreus exhibits intrinsic resistance to amphotericin B (AmB). The elevated MIC value for AmB aligns with the identification of the fungus as A. terreus.
Environmental Risk Factors
Construction activities increase the airborne spore load of Aspergillus, potentially contributing to infections in immunocompromised hosts (Aspergillus is an opportunistic pathogen).
Clinical Significance
The A. terreus species complex (SC) is a significant cause of invasive aspergillosis in immunocompromised patients. It ranks in isolation frequency after A. fumigatus SC and A. flavus SC. Less frequently, it has been associated with: allergic bronchopulmonary aspergillosis (ABPA), chronic aspergillosis, exacerbations of chronic obstructive pulmonary disease (COPD), external otitis.
Therapeutic Challenges
The intrinsic resistance of A. terreus to AmB complicates treatment, necessitating species-level identification of Aspergillus spp. for optimal management.
References
- Thakur R, Shishodia SK, Sharma A, Chauhan A, Kaur S, Shankar J. Accelerating the understanding of Aspergillus terreus: Epidemiology, physiology, immunology and advances. Curr Res Microb Sci. 2024; 6:100220. doi: 10.1016/j.crmicr.2024.100220 .
- Lass-Flörl C, Dietl AM, Kontoyiannis DP, Brock M. Aspergillus terreus Species Complex. Clin Microbiol Rev. 2021; 34(4):e0031120. doi: 10.1128/CMR.00311-20