Malassezia

Chapter 228 Malassezia

Members of the genus Malassezia include the causative agents of tinea versicolor and have been associated with other dermatologic conditions and with fungemia in patients with indwelling catheters. Malassezia are commensal lipophilic yeasts with a predilection for the sebum-rich areas of the skin. They are considered a part of the normal skin flora, with presence established by 3-6 mo of age.

The history of Malessezia nomenclature is complex and can be confusing. Because the yeast forms may be oval or round, these organisms were formally designated Pityrosporum ovale and Pityrosporum orbiculare. Newer technologies have allowed an improved classification system, with 13 recognized species. Only Malassezia pachydermatitis, a zoophilic yeast that causes dermatitis in dogs, is not lipophilic.

Transformation of the yeast form to a hyphal form facilitates invasive disease. The clusters of thick-walled blastospores together with the hyphae produce the characteristic spaghetti and meatballs appearance of Malassezia.

Malassezia globosa, M. sympodialis, M. restricta, and M. furfur are the major causes of tinea versicolor (Chapter 658). Malassezia organisms have also been associated increasingly with other dermatologic conditions. M. sympodialis and M. globosa have been implicated in neonatal acne, and M. globosa and M. restricta are most closely associated with seborrheic dermatitis and dandruff. Malassezia have also been causally associated with scalp psoriasis, pityrosporum folliculitis, and head and neck atopic dermatitis. Malassezia may be isolated from sebum-rich areas of asymptomatic persons, emphasizing that demonstration of the fungus does not equate with infection.

The traditional primary therapy for tinea versicolor is topical selenium sulfide 2.5% applied daily for at least 10 minutes for a week, followed by weekly to monthly applications for several months to prevent relapse. Additional topical agents that have efficacy include terbinafine, clotrimazole, and topical azoles. Malessezia-associated skin diseases limited to the head and neck can be managed with either 1% ciclopirox, ketoconazole, or zinc pyrithione shampoos.

Oral therapy for tinea versicolor with fluconazole, itraconazole, or ketoconazole is easier to administer, but it is more expensive and has higher side effect risks. Various dosing regimens have been used with success, including ketoconazole 200 mg daily for 7 days, fluconazole 400 mg as a single dose, and itraconazole 400 mg daily for 3-7 days. Regardless of the regimen chosen, patients should be encouraged to exercise while taking these medications in order to increase the skin concentration of the drug through sweating.

Despite successful treatment, repigmentation might not occur for several months. Relapses are common and can require repeat or alternative therapies.

M. furfur is the species most commonly causing fungemia, and M. pachydermatitis has been implicated in several outbreaks in neonatal intensive care units. The use of lipid emulsions containing medium-chain triglycerides inhibits the growth of Malassezia and can prevent infection. Infection is most common in premature infants, although immunocompromised patients, especially those with malignancies, can also be infected. Symptoms of catheter-associated fungemia are indistinguishable from other causes of cathether-associated infections (Chapter 172) but should be suspected in patients, especially neonates, receiving intravenous lipid infusions. Compared with other causes of fungal sepsis, it is unusual for catheter-related Malassezia fungemia to be associated with secondary focal infection.

Malassezia does not grow readily on standard fungal media, and successful culture requires overlaying the agar with olive oil. Recovery of Malassezia from blood culture is optimized by supplementing the medium with olive oil or palmitic acid.

Fungemia caused by M. furfur or other species can be successfully treated in most cases by immediately discontinuing the lipid infusion and removing the involved catheter. For persistent or invasive infections, amphotericin B (desoxycholate or lipid-complex formulations), fluconazole, and itraconazole are effective. Flucytosine has no activity against Malassezia.

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