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Malassezia

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).

RG-1 organisms.

Morphological Description: 
On media like modified Dixon’s agar, colonies are cream to yellowish, smooth or lightly wrinkled, glistening or dull, and with the margin being either entire or lobate. Malassezia is characterised by globose, oblong-ellipsoidal to cylindrical yeast cells. Reproduction is by budding on a broad base and from the same site at one pole (unipolar).

Molecular Identification:
ITS and D1/D2 sequencing may be used for accurate species identification (de Hoog et al. 2015).

MALDI-TOF MS: 
Capable of identifying all 14 Malassezia species in concordance with those of ITS sequence analyses (Kolecka et al. 2014).

Identification criteria for the differentiation of Malassezia species (de Hoog et. al. 2015).
+ Positive, - Negative, v Variable, w Weak, s Slow, nd No Data

Species Buds SDA 40C Cremophor
EL
Tween
80
Tween
60
Tween
40
Tween
20
Esculine Catalase
M. caprae narrow - - - + + + + + +
M. couiculi narrow - + - - - - - nd +
M. dermatis wide - + nd + + + + nd +
M. equina narrow - - - + + + + + +

M. furfur

wide - + + + + + w +

M. globosa

narrow - - - - - - - +
M. japonica wide - - nd - + w - nd +
M. nana narrow - v nd w + + v nd +

M. obtusa

wide - - - - - - + +

M. pachydermatis

wide + + -,w + + -,w v v

M. restricta

narrow - - - - - - - -

M. slooffiae

wide - + - +,w + + - +
M. sympodialis narrow - + -,w + + + + + +
M. yamatoensis wide - - nd + + + + nd +

References: 
Guillot and Gueho (1995), Gueho et al. (1996), Guillot et al. (1996, 2000), Boekhout et al. (2010), Cafarchia et al. (2011), de Hoog et al. (2015).

Antifungal Susceptibility: Very limited data available. Special growth conditions are needed for antifungal susceptibility testing; data from Nakamura et al. (2000), Velegraki et al. (2004) and Miranda et al. (2007); MIC µg/mL.
Antifungal Range MIC90 Antifungal  Range MIC90
FLU 0.125->64 4 (8) AmB 0.03-16 1 (8)
ITRA 0.03-16 0.125 VORI 0.03-16 0.125 (1)
KETO 0.03-4 0.25 POSA 0.03-32 0.125 (2)
Note: There is no standardised method and results are often variable, therefore susceptibility testing for guiding treatment is not recommended.

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