Malassezia yeasts -- everywhere and sometimes dangerous

Malassezia yeasts have been found in human dandruff, deep-sea vents, and pretty much everywhere in between. The skin of most if not all warm-blooded animals is covered with these microbes, and while they mostly live in peaceful co-existence with their hosts, they can cause serious diseases in humans and our furry friends. A Pearl (a short review) published on January 8th in PLOS Pathogens discusses the diseases caused by Malassezia, their detection, and treatment.

The article by Teun Boekhout, from the CBS-KNAW Fungal Biodiversity Center in Utrecht, The Netherlands, and colleagues from Greece and Italy, is the fifth and final one in a series on Malassezia, and focuses on its role as a pathogen. Most of the problems caused by Malassezia yeasts are skin diseases. Some of them, like dandruff and atopic eczema in humans or external ear infections in dogs, are very common.

While treatments exist for most of these, the researchers point out that when treating Malassezia skin diseases, "one should always bear in mind that Malassezia yeasts are integral components of the skin microbiota, and therefore the therapeutic target should be controlling the Malassezia population rather than eradicating it."

Malassezia bloodstream infections are less common, but premature infants and immunocompromised patients with extended stays in intensive care are at risk. Such infections are often linked to catheterization that facilitates internalization of the yeasts, either from the patient's own skin or from someone else's. Because routine tests in patients with blood infections of un-known origin often do not detect Malassezia right away, diagnosis might be delayed, which can be dangerous. However, once Malassezia is identified as the culprit, therapy with antifungal drugs is usually successful in eliminating the pathogen from the bloodstream.

As humans, we are covered head-to-toe with Malassezia--but that is not all. As Keisha Findley and Elisabeth Grice describe in their contribution to the series, healthy skin is actually cultivated by a well-balanced mix of bacteria and fungi (yeasts and molds), and this "skin flora" does not appear to elicit defense reactions by our immune system. How Malassezia interacts with other skin microbes is not yet known, but researchers think that both changes in the flora and changes in the immune system can disturb this peaceful equilibrium and lead to a range of skin diseases.

One of the reasons why, despite our intimate association, we do not know more about Malassezia, is that the yeasts cannot easily be isolated and grown in a laboratory environment. Malassezia are lipophilic, meaning they like fat. Human skin contains sebaceous glands that produce fats to lubricate and waterproof the skin, and Malassezia brakes down these fats and uses them as its main energy source.

As the yeasts metabolize the skin surface fat, they form break-down products that can potentially trigger harmful reactions by the skin. For example, Boekhout and colleagues discuss the intriguing possibility that Malassezia is involved in the development of skin cancer, because some of its fat breakdown products can activate known tumor-promoting pathways in the skin that are similar to those triggered by sun light.

How Malassezia strains that live in radically different environments (including the marine forms discussed by Anthony Amend in his Pearl) interact with their surroundings and obtain energy is still a mystery. However, Malassezia yeasts have been found pretty much any place scientists have looked for them--often in very large numbers--and are likely to play important roles in the both the healthy and diseased states of these environments.

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Contact:

Teun Boekhout
e-mail: t.boekhout@cbs.knaw.nl
phone: +31.30.212.2671

Keisha Findley
e-mail: keisha.findley@nih.gov

Joseph Heitman
e-mail: heitm001@dm.duke.edu

Please use this URL to provide readers access to the paper by Boekhout, et al. (Link goes live upon article publication): http://dx.plos.org/10.1371/journal. ppat.1004523

URLs to already-published Pearls in Malassezia series:

Grice & Findley: http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1004436

Amend: http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1004277

Cabañes: http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1003892

Heitman et al: http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1002701

Related Images for Press Use:
(Images are from the Pearl titled, "Malassezia Infections in Humans and Animals: Pathophysiology, Detection, and Treatment")

Malassezia yeasts might promote skin cancer similar to UV light.
Image Credit: Aristea Velegraki, National and Kapodistrian University of Athens, Greece. CC-BY http://www.plos.org/wp-content/uploads/2013/05/Pathogens_Mala_series_IMG_1.jpg

Pityriasis versicolor (left) and folliculitis (right); two skin diseases caused by Malassezia yeasts.
Image Credit: Aristea Velegraki, National and Kapodistrian University of Athens, Greece. CC-BY http://www.plos.org/wp-content/uploads/2013/05/Pathogens_Mala_series_IMG_2.jpg

Authors and Affiliations for the article by Boekhout, et al.:

Aristea Velegraki, National and Kapodistrian University of Athens, Greece

Claudia Cafarchia, University of Bari Aldo Moro, Italy

Georgios Gaitanis, University of Ioannina, Greece

Roberta Iatta, University of Bari Aldo Moro, Italy

Teun Boekhout, CBS-KNAW Fungal Biodiversity Centre, The Netherlands; Chinese Academy of Sciences, China; Second Military Medical University, China

Please contact plospathogens@plos.org if you would like more information.

Funding: This publication was supported by NPRP grant 5-298-3-086 from the Qatar National Research Fund (a member of the Qatar Foundation) to TB. The statements herein are solely the responsibility of the authors. GG and AV have received Procter and Gamble and L'Oreal research grants for Malassezia studies. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

Citation: Velegraki A, Cafarchia C, Gaitanis G, Iatta R, Boekhout T (2015) Malassezia Infections in Humans and Animals: Pathophysiology, Detection, and Treatment. PLoS Pathog 11(1): e1004523. doi:10.1371/journal.ppat.1004523

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