Seborrheic dermatitis (SD) is a chronic inflammatory dermatologic condition in which erythema and itching develop on areas of the body with sebaceous glands, such as the scalp, face and chest. The inflammation is evoked directly by oleic acid, which is hydrolyzed from sebum by lipases secreted by skin microorganisms. Although the skin fungal genus, Malassezia, is thought to be the causative agent of SD, analysis of the bacterial microbiota of skin samples of patients with SD is necessary to clarify any association with Malassezia because the skin microbiota comprises diverse bacterial and fungal genera. In the present study, bacterial microbiotas were analyzed at non-lesional and lesional sites of 24 patients with SD by pyrosequencing and qPCR. Principal coordinate analysis revealed clear separation between the microbiota of non-lesional and lesional sites. Acinetobacter, Corynebacterium, Staphylococcus, Streptococcus and Propionibacterium were abundant at both sites. Propionibacterium was abundant at non-lesional sites, whereas Acinetobacter, Staphylococcus and Streptococcus predominated at lesional sites; however, the extent of Propionibacterium colonization did not differ significantly between lesional and non-lesional sites according to qPCR. Given that these abundant bacteria hydrolyze sebum, they may also contribute to SD development. To the best of our knowledge, this is the first comprehensive analysis of the bacterial microbiotas of the skin of SD patients.

IntroductionSeborrheic dermatitis (SD) is a common inflammatory skin disorder associated with seborrhea. It is characterized by erythematous patches with yellow-gray scales. These appear most often on the face, especially the nasolabial folds, scalp, and upper trunk, in sebaceous gland-rich areas of the skin. The disorder is present in about 3% of the general population, more prevalent in males than in females, and frequently observed in patients with acquired immunodeficiency syndrome (AIDS) and Parkinson's disease [1,2]. The disease presents in two age groups: newborn infants up to 5 months of age, and young adults with increased sebum secretion from the skin.The human skin is populated by various microorganisms, including bacteria and fungi [3,4]. Of these, skin fungi, Malassezia species, play an important role in the development of SD. As Malassezia species require fatty acids for their growth, they colonize the sebaceous glandrich areas of the skin, including the face, scalp, and back, where they feed on fatty acids from human sebum. Malassezia species secrete lipases that hydrolyze sebum into triglycerides, which are further hydrolyzed into fatty acids [5][6][7]. Fatty acids are utilized as nutrition by skin microorganisms, including Malassezia. However, the unsaturated fatty acid oleic acid causes inflammation of the skin directly by eliciting IL-1α secretion from macrophages or epidermal keratinocytes, and is thought to be the causative agent of SD [7]. In fact, the mRNA expression of a specific Malassezia lipase gene can be detected from lesional sites in patients with SD [8,9]. The clinical condition improves on administering antifungal agents, suggesting that Malassezia species are one of the causative agents of SD [10,11]. Tajima et al. [12] analyzed the Malassezia microbiota in the skin of patients with SD using a DNA-based molecular approach. The genus Malassezia currently includes 14 species; of these, M. globosa and M. restricta are the major species in the skin of patients with SD and these species are more abundant at lesional sites than non-lesional sites.In the present study, we analyzed comprehensively the skin fungal microbiota of lesional and non-lesional sites of SD patients to obtain basic information to enable understanding of the development of SD and skin fungal microbiota using a pyrosequencing approach. Materials and Methods Patients and sample collectionTwenty-four Japanese outpatients with SD were enrolled in this study (19 males and 5 females; mean age 47.8 ± 18.8 (range 20-77) years). Patients who took antimicrobial agents before involvement in this study were excluded. The study protocol was approved by our Institutional Review Board and informed consent was obtained from each individual. AbstractBackground: Seborrheic dermatitis (SD) is an inflammatory disease associated with seborrhea that appears most often on the face, especially the nasolabial folds, scalp, and upper trunk, in sebaceous gland-rich areas of the skin. Although various factors are involved in the developmen...