DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
Penicillium is a very large and ubiquitous genus which currently contains 354 accepted
species (Visagie et al. 2014). Many species are common contaminants on various
substrates and are known as potential mycotoxin producers. Correct identification is
therefore important when studying possible Penicillium contamination of food. Human
pathogenic species are rare, however opportunistic infections leading to mycotic
keratitis, otomycosis and endocarditis (following insertion of valve prosthesis) have
been reported (Lyratzopoulos et al. 2002). Note: Penicillium marneffei and other
subgenus Biverticillium species have been transferred to the genus Talaromyces
(Samson et al. 2011b).
RG-1 organisms.
Penicillium Link: Fries
Morphological Description: Colonies are usually fast growing, in shades of green,
sometimes white, mostly consisting of a dense felt of conidiophores. Microscopically,
chains of single-celled conidia are produced in basipetal succession from a specialised
conidiogenous cell called a phialide. The term basocatenate is often used to describe
such chains of conidia where the youngest conidium is at the basal or proximal end of
the chain. In Penicillium, phialides may be produced singly, in groups or from branched
metulae, giving a brush-like appearance (a penicillus). The penicillus may contain both
branches and metulae (penultimate branches which bear a whorl of phialides). All cells
between the metulae and the stipes of the conidiophores are referred to as branches.
The branching pattern may be either simple (non-branched or monoverticillate),
one-stage branched (biverticillate-symmetrical), two-stage branched (biverticillateasymmetrical)
or three- to more-staged branched. Conidiophores are hyaline, smooth
or rough-walled. Phialides are usually flask-shaped, consisting of a cylindrical basal
part and a distinct neck, or lanceolate (with a narrow basal part tapering to a somewhat
pointed apex). Conidia are in long dry chains, divergent or in columns, are globose,
ellipsoidal, cylindrical or fusiform, hyaline or greenish, smooth or rough-walled. Sclerotia
are produced by some species.
phialides
metulae
branches
a b c d
Morphological structures and types of conidiophore branching in Penicillium.
(a) Monoverticillate; (b) Biverticillate; (c) Terverticillate; (d) Quaterverticillate
(see Visagie et al. 2014).