Aspergillus flavus

Aspergillus flavus

The specific filamentous fungus belongs to the Aspergillus genus; however, species-level identification based solely on macroscopic and microscopic characteristics is unreliable. In our case, it was identified as Aspergillus flavus using MALDI-TOF MS.

The colonies of A. flavus have a granular or cotton-like texture, with colors ranging from yellow, yellow-brown, to greenish-yellow (a). Microscopically, its vesicle is round at the base and bears one or two rows of phialides. The phialides in the first row are longer than those in the second row, though this distinction is not visible in the current image (b). This limitation is why species-level identification is often uncertain based on morphology alone.

Aspergillus flavus is ubiquitous in the environment. It grows on stored straw or cereals—animal feed—as well as on organic materials in decay (manure, garbage). Infection can occur either by inhaling the fungus’s spores (conidia), which settle in the alveoli of the lungs, or through a break in the skin/mucous membranes (trauma, catheter). The clinical picture depends directly on the immune status of the host. Specifically, infections of the paranasal sinuses can be classified into non-invasive (allergic fungal rhinosinusitis, aspergilloma) and invasive forms (chronic, chronic granulomatous, acute fulminant). The diagnosis of the invasive form is confirmed through histological examination. In this case, the patient had an underlying hematological disorder and had received corticosteroids.

Aspergillus flavus is the second most common species of Aspergillus – after A. fumigatus – to cause infections in humans. Its isolation is more frequent in areas with a dry and hot climate. A. flavus is one of the most common causes of fungal rhinosinusitis, and in several studies, it ranks higher than A. fumigatus in terms of frequency. Additionally, it exhibits high pathogenicity, which can partly be attributed to the production of mycotoxins.

[Case Editor: Anastasia Spiliopoulou, Assistant Professor of Microbiology, Medical School, University of Patras]

References

Hedayati MT, Pasqualotto AC, Warn PA, Bowyer P, Denning DW. Aspergillus flavus: human pathogen, allergen and mycotoxin producer. Microbiology 2007;153:1677-1692. doi: 10.1099/mic.0.2007/007641-0. PMID: 17526826.

Bougioukas L, Campbell B, Crooker K, Freed JA, Wilcock J, Singh D, Hale AJ. Invasive Aspergillus flavus sinusitis in an immunocompetent patient using intranasal cocaine. IDCases. 2021; 26:e01327. doi: 10.1016/j.idcr.2021.e01327. PMID: 34804802; PMCID: PMC8585617.