MALASSEZIA FURFUR: CHARACTERISTICS, PATHOLOGY AND TREATMENT - BIOLOGY - 2025

Malassezia furfur is a species of yeast fungus, the causative agent of superficial mycosis pityriasis versicolor, also called tinea or tinea versicolor. Its distribution is worldwide, but it is more frequent in tropical and temperate climates.

It represents 5% of mycoses in general and 20% of superficial mycoses. In summer, when it is hotter, endemics increase from 4% to 50%. It has been seen to affect both sexes with a slight predilection in women between the ages of 2 and 90, with an average of 20 to 30 years.

Malassezia furfur in direct smear / Pityriasis versicolor lesions

Children are affected in approximately 5 to 12%, between ages 8 to 11. The increase of this fungus from adolescence may be linked to hormonal factors where there is greater production of sebum in the skin.

However, other findings that include the presence of the fungus in babies in countries such as Thailand, suggests possible climatic and perhaps genetic factors in skin colonization.

Infection by this fungus does not have a predilection for races or social strata and is not very important in HIV patients, although it is frequent in patients with other immune deficiencies.

characteristics

Phylum: Basidiomycota

Class: Exobasidiomycetes

Order: Malasseziales

Family: Malasseziaceae

Genus: Malassezia

Species: furfur

Pathology

It is characterized by affecting the superficial layers of the skin, specifically the stratum corneum of the epidermis.

Invasion of the outer layers of the stratum corneum occurs after conversion from a yeast-like commensal to a filamentous parasite as a consequence of local immunological alterations.

Inflammation and scaling are believed to be the cause or consequence of fungal overpopulation. The fungus causes the appearance of erythematous macules, confluent with hypopigmented and hyperpigmented areas, associated with induration and desquamation.

The lesions are mainly located on the trunk and arms, but can also affect armpits, groin, arms, thighs, buttocks, shoulders, back, neck and face.

They present variable colors that go from pink to yellow-brownish and are sometimes achromatic. This is where the name versicolor comes from.

Color changes

Color changes in the skin occur by various mechanisms.

On the one hand, the fungus produces dicarboxylic acid, especially azelaic acid, and other tyrosinase-dependent lipid metabolites, such as pityriacitrine and pityrialactone, which act on melanocytes and inhibit dopa-tyrosinase. This mechanism manifests itself with hypochromia.

Whereas, hyperchromic lesions are due to the increase in size of melanosomes, for which there are two hypotheses:

• The first theory proposed is the increase in the thickness of the horny layer in dark-skinned individuals.
• The second raises the existence of an intense inflammatory infiltrate that would stimulate melanocytes, increasing melanin production.

The infection is usually asymptomatic, but occasionally there may be slight itching and redness of the skin.

Diagnosis

Ultraviolet light (Wood's Lamp)

If the lesions are passed an ultraviolet light, they will be observed with a greenish-yellow fluorescent coloration.

Skin scrap samples

The sample is taken with a scalpel, making a scrape, then mounted directly on a sheet with a drop of 20% KOH, plus Parker ink or methylene blue to highlight the structures.

Viewed under the light microscope, the fungus is usually observed as a group of budding yeast cells (in clusters) mixed with short curved hyphae, giving the appearance of spaghetti with meatballs.

Yeasts are oval or bottle-shaped, measuring 3 to 8 µm in diameter. They present with a monopolar bud with a septum in the cell wall where the bud leaves a scar.

Scotch tape

Adhesive tape is a very effective method for taking samples of lesions for direct examination. It consists of placing a piece of transparent adhesive tape over the injury, applying pressure to it, and then removing it in the opposite direction to the injury.

The tape is placed on a slide and viewed under a microscope with a 10x to 40x objective. Fixed preparations can also be made from the skin scales.

For sampling with any of the methods it is necessary that the patient has not been treated with fungicides or ointments. In areas subjected to frequent washing such as the face, the direct examination is not very effective.

Differential diagnosis

Differential diagnosis should be made with seborrheic dermatitis, pinta, vitiligo, erythrasma, pityriasis rosea, secondary syphilis, parasitic acromia and circinate ringworm.

Culture

The cultivation of the fungus is difficult, therefore it is not usually carried out, since with the previously explained methods the diagnosis can be made.

However, the fungus can grow on Sabouraud's dextrose agar or 5% sheep's blood agar, supplemented with long-chain fatty acids on their surface. For this you can use olive oil.

Malassezia furfur produces smooth, convex creamy colonies with rough variants. At Gram, elongated, spherical or oval cells are observed and some filaments can be visualized.

By electron microscopy, it is possible to see a multilaminar wall, thickened and with diagonal striations. Colonies develop slowly after 2 to 4 days of incubation at 35 ° C.

Treatment

Treatment consists of placing 1% selenium sulfide applied to the lesions every 3 days for 15 minutes, and then washing the area.

References

1. Ryan KJ, Ray C. Sherris. Medical Microbiology, 6th Edition McGraw-Hill, New York, USA; 2010.
2. Koneman E, Allen S, Janda W, Schreckenberger P, Winn W. (2004). Microbiological Diagnosis. (5th ed.). Argentina, Editorial Panamericana SA
3. Forbes B, Sahm D, Weissfeld A. Bailey & Scott Microbiological Diagnosis. 12 ed. Argentina. Editorial Panamericana SA; 2009.
4. Casas-Rincón G. General Mycology. 1994. 2nd Ed. Central University of Venezuela, Library Editions. Venezuela Caracas.
5. Arenas R. Illustrated Medical Mycology. 2014. 5th Ed. Mc Graw Hill, 5th Mexico.
6. González M, González N. Manual of Medical Microbiology. 2nd edition, Venezuela: Directorate of media and publications of the University of Carabobo; 2011.
7. Wikipedia contributors. Malassezia. Wikipedia, The Free Encyclopedia. November 6, 2018, 17:32 UTC. Available at.wikipedia.org
8. Thayikkannu AB, Kindo AJ, Veeraraghavan M. Malassezia-Can it be Ignored? Indian J Dermatol. 2015; 60 (4): 332-9.