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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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eTable 301.1. Currently Accepted Malassezia Species
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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 ...

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