DESCRIPTIONS OF MEDICAL FUNGI

Descriptions of Medical Fungi 119
Malassezia Baillon
Malassezia species are basidiomycetous yeasts and form part of the normal skin flora
of humans and animals. The genus now includes 14 species of which 13 are lipid
dependent. These include M. caprae (goat, horse), M. cuniculi (rabbit), M. dermatis
(human), M. equina (horse, cow), M. furfur (human, cow, elephant, pig, monkey, ostrich,
pelican), M. globosa (human, cheetah, cow), M. japonica (human), M. nana (cat, cow,
dog), M. obtusa (human), M. pachydermatis (dog, cat, carnivores, birds), M. restricta
(human), M. slooffiae (human, pig, goat, sheep), M. sympodialis (human, horse, pig
sheep) and M. yamatoensis (human) (Cabanes et al. 2011).
M. sympodialis, M. globosa, M. slooffiae and M. restricta are the most frequently found
species responsible for colonisation of humans (Arendrup et al. 2014).
Malassezia species may cause various skin manifestations including pityriasis versicolor,
seborrhoeic dermatitis, dandruff, atopic eczema and folliculitis. M. pachydermatis is
known to cause external otitis in dogs. Fungaemia due to lipid-dependent Malassezia
species usually occurs in patients with central line catheters receiving lipid replacement
therapy, especially in infants (Tragiannides et al. 2010, Gaitanis et al. 2012, Arendrup
et al. 2014).
Note: With the exception of M. pachydermatis, the primary isolation and culture of
Malassezia species is challenging because in vitro growth must be stimulated by
natural oils or other fatty substances. The most common method used is to overlay
Sabouraud’s dextrose agar (SDA) containing cycloheximide (actidione) with olive oil or
alternatively to use a more specialised media like modified Leeming and Notham agar
(Kaneko et al. 2007), or modified Dixon’s agar (see specialised culture media).
However, CHROMagar Malassezia medium is now commercially available for the
primary isolation and differentiation of the most common Malassezia species.
Comment: For clinical management at the level of the individual patient, species
identification is less important, although it is obviously needed for epidemiological
surveillance and outbreak investigation (Arendrup et al. 2014).
a
b
10 μm
Malassezia furfur (a) culture on modified Dixon’s agar and (b) direct microscopy of skin
scrapings showing characteristic clusters of thick-walled round, budding yeast-like cells
and short angular hyphal forms (the so called “spaghetti and meatballs” appearance)
typically seen in pityriasis versicolor.