Malassezia yeasts in seborrheic dermatitis and seborrhea

Malassezia yeasts are lipophilic organisms, commensals of the normal human cutaneous microbiota, and also agents of certain skin diseases such as seborrheic dermatitis (SD). The pathogenetic role of Malassezia in SD remains unclear. The relationship between SD and Malassezia is based on evidence that removal of the yeasts from the skin, using an antifungal agent, usually leads to remission. Based on the antiinflammatory properties and decreased sebum production, some authors have administered low-dose oral isotretinoin for moderate to severe SD and seborrhea. The purpose of this study was to analyse the prevalence of Malassezia species in the scalp skin of patients with SD and seborrhea prior and after therapy with 10 mg oral isotretinoin every other day and antiseborrheic shampoo, for six months. Sampling was performed from the scalp lesions and from clinically healthy skin of the scalp in seborrhea cases. Skin scales were scraped with a sterile cureta, processed and inoculated in the same day into modified Dixon agar. The cultures were inoculated and incubated at 32°C for 7 days. Malassezia species were identified according to their physiological and molecular characteristics. We used a PCR technique to amplify the fungal ITS and D1/D2 regions and the ITS and D1/D2 amplicons were sequenced. Forty five patients with SD and/or seborrhea with scalp involvement (30 females and 15 males, aged from 18 to 40years) were selected for the clinical trial. All participants signed a Consent Form after approval of the study by institutional review board. A total of 86 isolates were studied prior to and after the therapies. The results of culture were positive for Malassezia yeast in 92% cases. The predominant specie was M globosa, found in 46% isolates and the prevalence of other species was 30% for M restricta, 9%for Msympodialis, 3%for Mdermatis, 2% for M japonica and M furfur each and 1% for M slooffiae. Three species, M obtusa, M pachidermatis and M yamatoensis were not isolated. The prevalence of Malassezia species after therapies maintained similar to the baseline and no treatment group differences were noted. In fact, the reduced sebum secretion rate from the scalp environment was not sufficient to eliminate Malassezia yeasts in scalp lesions in subjects treated with low-dose oral isotretinoin or anti-seborrheic shampoo. We believe that the most adapted Malassezia yeasts remained in the scalp despite both therapies.