DESCRIPTIONS OF MEDICAL FUNGI

Descriptions of Medical Fungi 13
Aspergillus Micheli ex Link
Morphological Description: Colonies are usually fast growing, white, yellow, yellowbrown,
brown to black or shades of green, mostly consisting of a dense felt of erect
conidiophores. Conidiophores terminate in a vesicle covered with either a single
palisade-like layer of phialides (uniseriate) or a layer of subtending cells (metulae)
which bear small whorls of phialides (the biseriate structure). The vesicle, phialides,
metulae (if present) and conidia form the conidial head. Conidia are one-celled, smooth
or rough-walled, hyaline or pigmented, are produced in long dry chains which may be
divergent (radiate) or aggregated in compact columns (columnar). Some species may
produce Hülle cells or sclerotia.
For morphological identification, isolates are usually inoculated at three points on
Czapek Dox agar and 2% malt extract agar and incubated at 25 O C. Most species
sporulate within 7 days. Descriptions are primarily based on colony pigmentation and
morphology of the conidial head. Microscopic mounts are best made using cellotape
flag or slide culture preparations mounted in lactophenol cotton blue. A drop of alcohol
is usually needed to remove bubbles and excess conidia.
Key Features: Hyaline hyphomycete showing distinctive conidial heads with flaskshaped
phialides arranged in whorls on a vesicle.
References: Raper and Fennell (1965), Domsch et al. (1980), McGinnis (1980),
Onions et al. (1981), Samson and Pitt (1990, 2000), Samson et al. (1995), Samson
(1979), Vanden Bossche et al. (1988), Klich (2002), Steinbach et al. (2005), Samson
et al. (2011a, 2014), de Hoog et al. (2000, 2015).
conidia
phialides
vesicle
metulae
stipe
a
b
Conidial head morphology in Aspergillus (a) uniseriate, (b) biseriate.