
Malassezia

Malassezia (formerly known as Pityrosporum) is a genus of fungi. Malassezia is naturally found on the skin surfaces of many animals, including humans. In occasional opportunistic infections, some species can cause hypopigmentation or hyperpigmentation on the trunk and other locations in humans. Allergy tests for this fungus are available.
Nomenclature.
Due to progressive changes in their nomenclature, some confusion exists about the naming and classification of "Malassezia" yeast species. Work on these yeasts has been complicated because they require specific growth media and grow very slowly in laboratory culture.
"Malassezia" were originally identified by the French scientist Louis-Charles Malassez in the late 19th century. Raymond Sabouraud identified a dandruff-causing organism in 1904 and called it "Pityrosporum malassez", honoring Malassez, but at the species level as opposed to the genus level. When it was determined that the organisms were the same, the term "Malassezia" was judged to possess priority.
In the mid-20th century, it was reclassified into two species:
In the mid-1990s, scientists at the Pasteur Institute in Paris, France, discovered additional species.
Species.
, Species Fungorum accepts 22 species of "Malassezia". The following list gives the name of the fungus, the taxonomic authority (those who first described the fungus, or who transferred it into "Malassezia" from another genus; standardized author abbreviations are used), and the name of the organism from which the fungus was isolated, if not human.
Role in human diseases.
Dermatitis and dandruff.
Identification of "Malassezia" on skin has been aided by the application of molecular or DNA-based techniques. These investigations show that the "Malassezia" species causing most skin disease in humans, including the most common cause of dandruff and seborrhoeic dermatitis, is "M. globosa" (though "M. restricta" is also involved). The skin rash of tinea versicolor ("pityriasis versicolor") is also due to infection by this fungus.
As the fungus requires fat to grow, it is most common in areas with many sebaceous glands: on the scalp, face, and upper part of the body. When the fungus grows too rapidly, the natural renewal of cells is disturbed, and dandruff appears with itching (a similar process may also occur with other fungi or bacteria so differential diagnosis should be made).
A project in 2007 has sequenced the genome of dandruff-causing "Malassezia globosa" and found it to have 4,285 genes. "M. globosa" uses eight different types of lipase, along with three phospholipases, to break down the oils on the scalp. Any of these 11 proteins would be a suitable target for dandruff medications.
The number of specimens of "M. globosa" on a human head can be up to ten million.
"M. globosa" has been predicted to have the ability to reproduce sexually, but this has not been observed.
Research.
"Malassezia" is among the many mycobiota undergoing laboratory research to investigate whether it is associated with types of disease.