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
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Left= an agar air plate exposed for 2 minutes after the barley had been turned. showing numerous colonies of the fungus following incubation at 26C on 2% malt agar.Right= A sputum sample taken from a maltworker after exposure showing many fungal colonies when cultured on agar. His commensal yeast flora is seen towards the right base as cream/white colonies.
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growing on contaminated barley malt. The deep blue-green heads made up of chains of conidia are seen on the left. On the right, conidiophores from which conidial chains are developed show typical clavate heads. Stain- Cotton blue in Lactophenol.
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Sections of colonised alveoli
On the left, the conidiophores sporulate freely, on the right they are seen to cease development at the phialide stage. Carbon deposits are clearly seen here.A=alveolus, As=alveolar septum, C=conidiophore, P=phialide
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The growth isolated from the aspergilloma in the presence of living cells of the three bacterial species in culture.The most marked inhibition occurred with Pseudomonas aeruginosa(P) and Haemophilus influenzae(H) and to a much lesser extent with Staphylococcus aureus(S). C=control. Inhibitory factors were components of the bacterial slime layers.
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aspergilloma removed from the lung cavity seen in section.Staining was with methenamine/silver and light green. The structure shows zonation probably due to variations in the growth rate of mycelium(deep brown). A mucus layer(stained green) containing cell debris and bacteria is seen shrouding the fungus. Bacterial genera were Staphylococcus, Haemophilus and Pseudodomonas.
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Plugs cultured on agarA young colony of the fungus(AF) has a central patch of sporulation and is surrounded by colonies of bacteria and yeasts.
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A part of the mycelium in a stained sputum plug showing the dichotomously branched hyphae of Aspergillus fumigatus.
