Molecular identification of Malassezia species isolated from dermatitis affections

Epidemiological characterization of pityriasis versicolor and distribution of Malassezia species among students in Hai Phong city, Vietnam

Background and Purpose:

Pityriasis versicolor (PV) is a common fungal skin infection caused by Malassezia species. Previous studies have shown that the prevalence of PV is influenced by geographic factors. The aim of the current study was to find the epidemiological characteristics of PV and distribution of Malassezia species in the secondary school students living in Hai Phong city, Vietnam.

Materials and Methods:

This study was conducted on 1357 students within the age range of 10 - 16 years selected from four secondary schools in Hai Phong city. The students were screened for PV skin lesions from August 2016 to December 2017. The isolates of Malassezia from PV patients were analyzed by performing direct microscopy and culturing on modified Dixon agar plates, containing gentamicin, at 32oC for 7 days. In the next stage, the fungal strains obtained from patients with positive fungal cultures were identified using the CHROMagarTM Malassezia medium, polymerase chain reaction-restriction fragment length polymorphism techniques, and D1/D2 rDNA genome sequencing.

Results:

Pityriasis versicolor was diagnosed in 305 (22.48%) students and confirmed by clinical appearance and direct examination. A total of 293 (96.07%) samples grew on modified Dixon agar. With regard to demographic characteristics, 50.49% of the PV cases were female, and 57.38% of cases resided in urban areas. Furthermore, 88.52% of the subjects had the illness duration of more than 6 months. Hypopigmented and erythematous skin lesions were also observed in the research participants, with hypopigmentation being the most frequent condition (97.05%). Most of the Malassezia fungal strains were isolated from the back (39.56%), face (23.99%), and chest (16.51%). Malassezia furfur and M. japonica accounted for PV in 96.25% and 3.75% of the cases, respectively. Furthermore, Malassezia furfur was distributed in both rural and urban areas, while M. japonica was found only in the urban areas.

Conclusion:

The findings of the present study were indicative of the high prevalence of Malassezia yeasts, mostly M. furfur, among the students in Hai Phong city, Vietnam

Distribution of Malassezia species on the skin of patients with atopic dermatitis, psoriasis, and healthy volunteers assessed by conventional and molecular identification methods

Background

The Malassezia yeasts which belong to the physiological microflora of human skin have also been implicated in several dermatological disorders, including pityriasis versicolor (PV), atopic dermatitis (AD), and psoriasis (PS). The Malassezia genus has repeatedly been revised and it now accommodates 14 species, all but one being lipid-dependent species. The traditional, phenotype-based identification schemes of Malassezia species are fraught with interpretative ambiguities and inconsistencies, and are thus increasingly being supplemented or replaced by DNA typing methods. The aim of this study was to explore the species composition of Malassezia microflora on the skin of healthy volunteers and patients with AD and PS.

Methods

Species characterization was performed by conventional, culture-based methods and subsequently molecular techniques: PCR-RFLP and sequencing of the internal transcribed spacer (ITS) 1/2 regions and the D1/D2 domains of the 26S rRNA gene. The Chi-square test and Fisher’s exact test were used for statistical analysis.

Results

Malassezia sympodialis was the predominant species, having been cultured from 29 (82.9%) skin samples collected from 17 out of 18 subjects under the study. Whereas AD patients yielded exclusively M. sympodialis isolates, M. furfur isolates were observed only in PS patients. The isolation of M. sympodialis was statistically more frequent among AD patients and healthy volunteers than among PS patients (P < 0.03). Whether this mirrors any predilection of particular Malassezia species for certain clinical conditions needs to be further evaluated. The overall concordance between phenotypic and molecular methods was quite high (65%), with the discordant results being rather due to the presence of multiple species in a single culture (co-colonization) than true misidentification. All Malassezia isolates were susceptible to cyclopiroxolamine and azole drugs, with M. furfur isolates being somewhat more drug tolerant than other Malassezia species.

Conclusions

This study provides an important insight into the species composition of Malassezia microbiota in human skin. The predominance of M. sympodialis in both normal and pathologic skin, contrasts with other European countries, reporting M. globosa and M. restricta as the most frequently isolated Malassezia species.

The role of L-DOPA on melanization and mycelial production in Malassezia furfur

Melanins are synthesized by organisms of all biological kingdoms and comprise a heterogeneous class of natural pigments. Certain of these polymers have been implicated in the pathogenesis of several important human fungal pathogens. This study investigated whether the fungal skin pathogen Malassezia furfur produces melanin or melanin-like compounds. A melanin-binding monoclonal antibody (MAb) labelled in vitro cultivated yeast cells of M. furfur. In addition, melanization of Malassezia yeasts and hyphae was detected by anti-melanin MAb in scrapings from patients with pityriasis versicolor. Treatment of Malassezia yeasts with proteolytic enzymes, denaturant and concentrated hot acid yielded dark particles and electron spin resonance spectroscopy revealed that these particles contained a stable free radical compound, consistent with their identification as melanins. Malassezia yeasts required phenolic compounds, such as L-DOPA, in order to synthesize melanin. L-DOPA also triggered hyphal formation in vitro when combined with kojic acid, a tyrosinase inhibitor, in a dose-dependent manner. In this respect, L-DOPA is thought to be an essential substance that is linked to both melanization and yeast-mycelial transformation in M. furfur. In summary, M. furfur can produce melanin or melanin-like compounds in vitro and in vivo, and the DOPA melanin pathway is involved in cell wall melanization.

Diagnostic procedures in dermatology

Although most skin diseases can be diagnosed with simple visual inspection, laboratory investigations are necessary in several clinical circumstances. This contribution highlights the usefulness of routine diagnostic procedures that are often overlooked and the innovative methods of molecular biology, which are expensive and require an experienced staff. Among the classic diagnostic investigations are (1) the use of Wood's light in many dermatologic disorders (eg, vitiligo, pityriasis versicolor, erythrasma, porphyrias), (2) cytodiagnosis of Tzanck in dermatologic practice (eg, herpetic infections, molluscum contagiosum, leishmaniasis, pemphigus vulgaris, basal cell carcinoma, erythroplasia of Queyrat, Hailey-Hailey disease), and (3) microscopic examination for fungal and bacterial skin infections as well as for mite infestation using potassium hydroxide, simple saline, and Gram stain. Modern molecular biotechnologies encompassing gene-specific polymerase chain reaction and its variants have a substantial affect in selected cases of viral (especially herpes simplex virus), bacterial, fungal, and protozoan (Leishmania) skin infections.