**Atopic Dermatitis and Skin Fungal Microorganisms**

Takashi Sugita1, Enshi Zhang3, Takafumi Tanaka1, Mami Tajima3, Ryoji Tsuboi3, Yoshio Ishibashi2, Akemi Nishikawa2 *1Department of Microbiology, Meiji Pharmaceutical University, Kiyose, Tokyo 2Department of Immunobiology, Meiji Pharmaceutical University, Kiyose, Tokyo 3Department of Dermatology, Tokyo Medical University, Shinjuku, Tokyo Japan* 

### **1. Introduction**

122 Atopic Dermatitis – Disease Etiology and Clinical Management

Sugita, T., Tajima, M., Amaya, M., Tsuboi, R., & Nishikawa, A. (2004). Genotype analysis

*Dermatological Science* Vol. 51, No. 2, pp. 113-120

pp.755-759

filaggrin gene by novel shotgun method in Japanese atopic dermatitis. *Journal of* 

of *Malassezia restricta* as the major cutaneous flora in patients with atopic dermatitis and healthy subjects. *Microbiology and Immunology* Vol. 48, No. 10,

> A wide variety of bacteria and fungi are found on the human skin. Although some skin microorganisms produce antibacterial peptides that inhibit invasion by pathogens or promote the integrity of cutaneous defenses by eliciting host immune responses, the normal microbiome can also cause several skin diseases.

> Atopic dermatitis (AD) is a chronic disease that causes pruritus and involves cycles of remission and deterioration. AD is the result of dry hypersensitive skin. When the skin is dry, the protective barrier function of the cutaneous surface horny layer is compromised, and the skin readily develops dermatitis in response to various external stimuli, including skin microorganisms. Serum from almost all AD patients contains IgE antibodies against some skin microorganisms. For example, staphylococcal superantigen-specific IgE is present in the serum of AD patients, but not in the serum of healthy individuals. Normally, the weakly acidic condition of healthy skin prevents colonization by *Staphylococcus aureus*. However, in patients with AD, the skin pH is shifted toward neutrality, allowing *S*. *aureus* to grow and exacerbate AD.

> In the cutaneous fungal microbiome, lipophilic yeasts of the genus *Malassezia* are the predominant species on human skin. As *Malassezia* species require lipids for growth, they preferentially colonize sebum-rich areas such as the head, face, and neck, as opposed to the limbs or trunk. Specific IgE antibody against *Malassezia* species is found in the serum of AD patients. Antifungal therapy improves the symptoms of AD by decreasing the level of *Malassezia* colonization, suggesting that these microorganisms also exacerbate AD. *Malassezia* species, unlike *S*. *aureus*, colonize both AD patients and healthy subjects. Currently, the genus *Malassezia* consists of 14 species. Of these, *M*. *globosa* and *M*. *restricta* have been detected in almost all AD patients, suggesting that these two *Malassezia* species play a significant role in AD. The level of specific IgE antibody against both species is greater than that against other *Malassezia* species.

This chapter discusses cutaneous fungi as an exacerbating factor in AD, focusing on:


Atopic Dermatitis and Skin Fungal Microorganisms 125

*slooffiae* in 21.4, 14.3, 7.1, and 3.6% of samples from Japanese AD patients, respectively. A study conducted in Sweden in 2005 produced similar results (Sandström *et al*. 2005). However, a Canadian study by Gupta *et al*. (2001) reported the predominant species to be *M. sympodialis*, which was detected in 51.3% of the samples from AD patients. All of these studies were performed using culture-dependent methods. In all cases, scale samples were collected by an appropriate method, e.g., swabbing, scratching, or stripping, and were incubated in medium containing several types of fatty acids. The recovered microorganisms were identified based on biochemical or physiological characteristics, including assimilation of Tween compounds and esculin, catalase reaction, and maximum growth temperature (Guého-Kellermann 2010; Kaneko *et al*. 2007). However, culture-dependent methods may not provide accurate and reliable results for *Malassezia*. The efficiency of culturing *Malassezia* strains depends on the isolation medium used, and the growth of some species, such *M.* 

*obtusa* and *M. restricta*, is slower than that of others.

Fig. 1. Morphology of *Malassezia restricta* by scanning electron microscope

To overcome the difficulties of culture-dependent methods, including scale sampling methods, culturing conditions, and isolation techniques, Sugita *et al*. (2001) developed the first molecular analytical method for *Malassezia*. For this method, scale samples are collected by stripping with medical transparent dressing, and skin *Malassezia* DNA is directly extracted from the dressing. The *Malassezia* microbiota is then analyzed by realtime PCR, specific detection by PCR with a species-specific primer, or an rRNA clone method (Sugita *et al*. 2011). Although more expensive than culture-dependent methods, a

Magnification is x5,000.
