According to earlier reports, M. sympodialis
, M. globosa
and M. furfur
were the most commonly isolated Malassezia
species from healthy individuals and from patients with diseases like atopic dermatitis11-16
. M. restricta
and M. globosa
were the most frequently isolated species in a Korean study17
. However, there were differences with a respect to the commonly isolated species, not only between normal healthy individuals and the patients with various skin diseases, but also between different countries. For the healthy subjects from a previous study, the dominant species was M. globosa18
, while M. sympodialis
was the dominant species in a study from Canada12
. For the patients with AD in this study, the dominant species was M. sympodialis
, while M. furfur15
or M. globosa
and M. restricta16
were the dominant species in Japan and M. sympodialis
was the dominant species in Canada13
. This difference may be attributable to the sampling and culture techniques such as our swabbing-culture-PCR-RFLP technique or the Opsite-nonculture-PCR-RFLP, as well as to racial and geographical differences.
The results from each body site indicated that M. restricta was the most common species on the scalp (30.0%) and cheek (16.7%). M. sympodialis (28.3%) was the most common species of AD patients on the chest (). The detection rate was lower on the thigh and upper arm among the different body sites. There could be a relationship among the prevalence sites of atopic dermatitis, the culture rate and the different isolated species, although this has not been clearly identified.
We understand that several subtypes of Malassezia may coexist on the same individual. We actually have confirmed the isolation of more than one subtype during the culture and PCR-RFLP process. However, in this study, the results were derived from the dominant subtypes (the dense band on PCR-RFLP).
In this study, the prevalence of the Malassezia
yeasts was lower for the AD patients as compared to that of the healthy subjects from a previous study18
. Further proof is needed for our observation that patients with AD harbor a lower number of Malassezia
yeasts. One reason for this may be the reduced amount of lipids in the skin of AD patients19
. In a recent study, the number of yeast cells on patients with AD was lower in the lesional skin as compared to that of the nonlesional skin. In a previous study, cultures from the lesional skin of patients with AD were, for approximately 25% of the subjects, taken from the arm or leg, which are locations known to harbor Malassezia
less often than the trunk, neck and forehead20
. Another explanation may be the antifungal activity of the mediators and/or inflammatory cells present in AD lesions. According to recent studies, Malassezia
may be an important allergen and trigger factor in AD, and especially for the AD located in the head and neck region21,22
. In this current study, the prevalence of positive Malassezia
cultures was not higher for the patients with severe AD or a SCORAD≥40, as compared with those patients who had a SCORAD<40. The role of Malassezia
yeasts as a trigger factor in AD is probably due to an allergic reaction. There was no difference between positive cultures of different Malassezia
species and the severity of AD. Quantitative analysis like RT-PCR may be needed to clarify the relationship between Malassezia
and atopic dermatitis.
From this study, the recovery rate from AD was lower than that of other studies. The reason for this is the limitation of the age group from 0 to 30. Atopic dermatitis is a chronic, fluctuating, inflammatory skin disease that rarely presents in adulthood; it commonly occurs within the first 2 years after the birth. The worldwide prevalence of AD is 10~20% in children and 1~3% in adults23
. So in this study, we enrolled AD patients from the 0~30 age group, and not from the AD patients of all ages. Our result of the distribution of the Malassezia
species was similar to that of many previous studies, but the recovery rate was lower. In many recent studies, real time PCR or nested PCR were popularly used for identifying the Malassezia
species. However, 26S rDNA PCR RFLP is a genotypic identification approach that can be applied for identifying nearly all known Malassezia
species and it is a flexible procedure because patterns of newly described species can be added directly to a database without the need for sequence information. This PCR-RFLP method requires only PCR and one or two enzymes, and it is technically less demanding than most other molecular biological approaches12
. Lee et al.24
previously compared the obtained DNA sequences with the full sequences of the genes already available in GeneBank, and this showed 99% concordance. Oh et al.25
species using nested PCR from the 327 positive samples, with those samples with 2 or more identified yeasts being excluded. As a result, 320 out of the 327 samples (98.8%) were concordant with the results of the RFLP method. Thus, the 26S rDNA PCR-RFLP method for identifying 11 Malassezia
species is capable of identifying species with high accuracy and reliability, and it is simple, fast and cost effective for use even in routine laboratories.
In conclusion, we found fewer individuals with positive Malassezia cultures among the AD patients. It was also confirmed that the prevalence of a positive Malassezia culture was not correlated with the severity of AD.
This makes it rather difficult to elucidate the role of Malassezia in atopic dermatitis on the basis of the detection rate alone. The relationship between atopic dermatitis and the Malassezia species should be clarified through further studies.
The species cultured from the AD patients' skin differed from that of the normal skin, as much it varied among different locations of AD lesions. These facts may be due to disrupted skin barrier function and the sensitization to the organism that's induced by scratching in AD lesions. In order to determine the distribution and the character of Malassezia yeasts on the skin of AD patients, more case control studies and quantitative molecular biologic analysis should be done by selecting specific types of subjects from AD patients.