Date: 26 November 2013
Aspergillus flavus
Copyright:
© Fungal Research Trust
Notes:
Colonies on CYA 60-70 mm diam, plane, sparse to moderately dense, velutinous in marginal areas at least, often floccose centrally, sometimes deeply so; mycelium only conspicuous in floccose areas, white; conidial heads usually borne uniformly over the whole colony, but sparse or absent in areas of floccose growth or sclerotial production, characteristically Greyish Green to Olive Yellow (1-2B-E5-7), but sometimes pure Yellow (2-3A7-8), becoming greenish in age; sclerotia produced by about 50% of isolates, at first white, becoming deep reddish brown, density varying from inconspicuous to dominating colony appearance and almost entirely suppressing conidial production; exudate sometimes produced, clear, or reddish brown near sclerotia; reverse uncoloured or brown to reddish brown beneath sclerotia. Colonies on MEA 50-70 mm diam, similar to those on CYA although usually less dense. Colonies on G25N 25-40 mm diam, similar to those on CYA or more deeply floccose and with little conidial production, reverse pale to orange or salmon. No growth at 5°C. At 37°C, colonies usually 55-65 mm diam, similar to those on CYA at 25°C, but more velutinous, with olive conidia, and sometimes with more abundant sclerotia.
Sclerotia produced by some isolates, at first white, rapidly becoming hard and reddish brown to black, spherical, usually 400- 800 µm diam. Teleomorph not known. Conidiophores borne from subsurface or surface hyphae, stipes 400 µm to 1 mm or more long, colourless or pale brown, rough walled; vesicles spherical, 20-45 µm diam, fertile over three quarters of the surface, typically bearing both metulae and phialides, but in some isolates a proportion or even a majority of heads with phialides alone; metulae and phialides of similar size, 7-10 µm long; conidia spherical to subspheroidal, usually 3.5-5.0 µm diam, with relatively thin walls, finely roughened or, rarely, smooth.
Distinctive features
Aspergillus flavus is distinguished by rapid growth at both 25°C and 37°C, and a bright yellow green (or less commonly yellow) conidial colour. A. flavus produces conidia which are rather variable in shape and size, have relatively thin walls, and range from smooth to moderately rough, the majority being finely rough.
Images library
-
Title
Legend
-
The chest x-ray shows a patient who had a left lung transplanted in May 2003 for cryptogenic fibrosing alveolitis, which was diagnosed post-transplant as sarcoidosis.
-
Gross pathology demonstrating the great pleural thickness and two cavities (upper lobe and superior segment of lower lobe) with fragments of fungal mass.
-
Histopathological appearance of a fungus ball. Note a conidial head resulting from fungal exposure to the air.
-
Histopathological appearance of a fungus ball caused by Scedosporium apiospermum. The presence of anneloconidia differentiates it from Aspergillus.
-
Chronic necrotising aspergillosis. Hyaline hyphal and calcium oxalate crystals obtained by needle aspirate biopsy from a diabetic patient with chronic necrotizing aspergillosis caused by Aspergillus niger (Papanicolaou, x 100).
-
Aspergillus niger fungus ball and acute oxalosis. Higher magnification of adjacent replicate section.
-
Oxalate crystals within renal tubuli (H&E, phase contrast, x 100). This patient developed acute oxalosis.
-
Lung surface. Fungus ball, severe parenchymal fibrosis and pleural thickening.