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The genus Malassezia includes
11 species associated with significant human disease1(eTable 301.1). The organisms are dimorphic with
both yeast and mycelial growth. With the exception of M
pachydermatis, all other Malassezia species
require lipid supplementation of standard fungal growth media for
isolation. When Sabouraud media is overlaid with sterile olive oil, Malassezia species
grow within 5 to 14 days.2 Isolation on this medium causes
colonies to coalesce, making species identification difficult. Although
species identification is rarely important in clinical practice,
several commercial media avoid this problem. Dixon medium (containing
Tween 40 and glycerol monooleate) and Leeming and Notman agar (containing
Tween 60, glycerol, and full-fat cow milk) are selective media for Malassezia isolation. Rapid
identification techniques, such as identification of Malassezia DNA
by polymerase chain reaction, have been utilized in study settings.3 Malassezia species
are normal residents of human skin, usually found in sebum-rich
areas such as the trunk, face, and scalp. Extensive studies on skin
colonization have shown that the skin of healthy newborn infants
becomes colonized with Malassezia species within
the first several months of life. Over 50% of prematurely
born infants requiring prolonged hospitalization become colonized
within 2 weeks of life.4,5 Ninety to 100% of
adolescents and adults have saprophytic skin colonization with Malassezia species.6
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Clinical Manifestations
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Skin diseases are the most common manifestation of Malassezia infection.7 Confirmed dermatoses
include tinea versicolor, seborrheic dermatitis, and folliculitis.
Tinea versicolor (Fig. 367-9) is disscussed
in Chapter 367. Lesions are most commonly seen on the chest, back,
and upper arms and occur most often in adolescents and young adults.
In those who develop tinea versicolor, the yeast phase transforms
to the mycelial phase. This results in the characteristic “spaghetti
and meatballs” appearance of skin scrapings when examined
under the microscope with 10% potassium hydroxide. Heat,
moisture, and skin occlusion favor this transformation. M
globosa, M restricta, and M sympodialis are
most often associated with tinea versicolor.
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Seborrheic dermatitis due to Malassezia occurs
in 2% to 5% of normal hosts but is prevalent in
70% to 80% of persons with untreated AIDS. This
condition varies from thick greasy scales covering the scalp of
infants in the first 3 months of life (cradle cap) to an itchy,
papular, erythematous, greasy, scaling rash most commonly found
in the nasolabial folds, postauricular scalp, eyebrows, or chest.9 Dandruff,
presenting as mildly pruritic scaling of the scalp without associated inflammation,
is felt to represent a milder variant of seborrheic dermatitis.
Diagnosis of seborrheic dermatitis and dandruff are usually made
on a clinical basis. Culture for Malassezia does
not confirm the ...