Some species of Malassezia are found on the skin of animals, including humans. Because malassezia requires
fat to grow,[3] it is most common in areas with many
sebaceous glands—on the scalp,[4] face, and upper part of the body.
Role in human diseases
Malassezia infections of human skin can cause or aggravate a variety of conditions, including dandruff, seborrheic dermatitis, and acne.[5]
(It is believed that the 18-century French revolutionary
Jean-Paul Marat suffered from a Malassezia restricta infection, which lead to his frequent bathing in a medicinal substance.[6])
Dermatitis and dandruff
When Malassezia grows too rapidly, the natural renewal of cells is disturbed, and dandruff can appear with itching (a similar process may also occur with other fungi or bacteria).
Identification of Malassezia on skin has been aided by the application of molecular or DNA-based techniques. These investigations show that the M. globosa is the species that causes most skin disease in humans, and that it is the most common cause of
dandruff and
seborrhoeic dermatitis (though M. restricta is also involved).[7]
There can be as many as ten million M. globosa organisms on a human head.[4]
A project in 2007 sequenced the genome of dandruff-causing Malassezia globosa and found it to have 4,285 genes.[8][9]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.
Prescription and over-the-counter shampoos containing
ketoconazole are commonly used to treat dandruff caused by Malassezia.
M. globosa has been predicted to have the ability to reproduce sexually,[10] but this has not been observed.
The skin rash of
tinea versicolor (pityriasis versicolor) is also caused infection by this fungus.
Cancer
Translocation of Malassezia species from the intestines into pancreatic neoplasms has been associated with
pancreatic ductal adenocarcinoma, and the fungi may promote tumor progression through activation of host
complement.[11][12]
Crohn's and inflammatory bowel disease
M. restricta, which is normally found in the skin, is linked to disorders like
Crohn's disease and
inflammatory bowel disease when found in the gut. This is especially true for organism with the N12
CARD9 allele, which provokes a stronger inflammatory response.[13]
Malassezia is the sole genus in
familyMalasseziaceae, which is the only family in
orderMalasseziales, itself the single member of
classMalasseziomycetes.[17]
Due to progressive changes in their nomenclature, some confusion exists about the naming and classification of Malasseziayeast species. Work on these yeasts has been complicated because they require specific
growth media and sometimes grow very slowly in
laboratory culture.[18]
Malassezia was originally identified by the French scientist
Louis-Charles Malassez in the late nineteenth century;[19] he associated it with the condition
seborrhoeic dermatitis.[20]Raymond Sabouraud identified a
dandruff-causing organism in 1904 and called it Pityrosporum Malassezii,[21] 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.[22]
In the mid-twentieth century, it was reclassified into two species:
Pityrosporum (Malassezia) ovale, which is
lipid-dependent and found only on humans. P. ovale was later divided into two species, P. ovale and P. orbiculare, but current sources consider these terms to refer to a single species of fungus, with M. furfur the preferred name.[23]
Pityrosporum (Malassezia) pachydermatis, which is lipophilic but not lipid-dependent. It is found on the skin of most animals.
Malassezia is the sole genus in the family Malasseziaceae, which was validated by Cvetomir Denchev and
Royall T. Moore in 2009.[24] The order Malasseziales had been previously proposed by Moore in 1980,[25] and later emended by Begerow and colleagues in 2000. At this time the order was classified as a member of
unknown class placement in the subdivision
Ustilaginomycotina.[26] In 2014, Cvetomir and Teodor Denchev
circumscribed the class Malasseziomycetes to contain the group.[27]
Description
Malassezia grows rapidly, typically maturing within 5 days when incubated at temperatures ranging from 30–35 °C (86–95 °F). Growth is slower at 25 °C (77 °F), and certain species struggle at 37 °C (99 °F). These organisms can proliferate on media infused with
cycloheximide. An essential factor for the growth of Malassezia is the presence of
long-chain fatty acids, with M. pachydermatis being an exception. The most conventional cultivation method involves overlaying solid media with a layer of
olive oil. However, for nurturing some clinically relevant species, such as the challenging-to-cultivate M. restricta, more intricate culture media may be required. For the most efficient recovery of Malassezia, it has been recommended to collect blood through a lipid infusion
catheter and subsequently use lysis-centrifugation—a recommendation backed by multiple comparative studies.[28]
The yeast-like cells of Malassezia, measuring between 1.5–4.5
μm by 3–7 μm, are characterised as
phialides featuring tiny collarettes (a small, collar-like flange or lip at the mouth of a phialide from which spores or conidia are produced and released). These collarettes are challenging to identify using standard
light microscopes. A defining characteristic of cells from this genus is their
morphology: one end is round, while the other has a distinctly blunt termination. This latter end is where singular, broad-based bud-like structures emerge, although in certain species, these structures might be narrower. To effectively visualise the organism's shape, a
staining technique involving
safranin is recommended, followed by observation under
oil immersion. Furthermore,
Calcofluor-white staining provides an enhanced clarity of the cell wall and its unique contour. While Malassezia typically lacks
hyphal elements, rudimentary forms can sporadically be present.[28]
Species
The Index Fungorum lists 22 species of Malassezia.[29] The following list gives the name, 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.
In the mid-1990s, scientists at the
Pasteur Institute in Paris, France, discovered additional species.[3]
^
abGuého E, Midgley G, Guillot J (May 1996). "The genus Malassezia with description of four new species". Antonie van Leeuwenhoek. 69 (4): 337–355.
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10.1007/BF00399623.
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^Ran Yuping (2016). "Observation of Fungi, Bacteria, and Parasites in Clinical Skin Samples Using Scanning Electron Microscopy". In Janecek, Milos; Kral, Robert (eds.). Modern Electron Microscopy in Physical and Life Sciences. InTech.
doi:
10.5772/61850.
ISBN978-953-51-2252-4.
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^Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby.
ISBN978-1-4160-2999-1.
^James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier.
ISBN0-7216-2921-0.
^Malassez, L. (1874). "Note sur le champignon du pityriasis simple" [Note on the fungus of simple pityriasis]. Archives of Physiology and Biochemistry (in French). 2: 451–464.
^Moore, R.T. (1980). "Taxonomic proposals for the classification of marine yeasts and other yeast-like fungi including the smuts". Botanica Marina. 23 (6): 361–373.
^Begerow, Dominik; Bauer, Robert; Boekhout, Teun (2000). "Phylogenetic placements of ustilaginomycetous anamorphs as deduced from nuclear LSU rDNA sequences". Mycological Research. 104 (1): 53–60.
doi:
10.1017/s0953756299001161.
^Denchev, C.M.; Denchev, T.T. (2014).
"Nomenclatural novelties"(PDF). Index Fungorum. 145: 1.
Archived(PDF) from the original on 2015-02-06. Retrieved 2021-12-06.
^
abLarone, Davise Honig (2011). Medically Important Fungi (5th ed.). Washington (D.C.): ASM press. p. 146.
ISBN978-1-55581-660-5.
^Cabañes, F.J.; Coutinho, S.D.A.; Puig, L.; Bragulat, M.R.; Castellá, G. (2016). "New lipid-dependent Malassezia species from parrots". Revista Iberoamericana de Micología. 33 (2): 92–99.
doi:
10.1016/j.riam.2016.03.003.
PMID27184440.
^White, S.D.; Vandenabeele, S.I.J.; Drazenovich, N.L.; Foley, J.E. (March 2006). "Malassezia Species Isolated from the Intermammary and Preputial Fossa Areas of Horses". Journal of Veterinary Internal Medicine. 20 (2): 395–398.
doi:
10.1111/j.1939-1676.2006.tb02874.x.
PMID16594600.
^Guého, E.; Midgley, G.; Guillot, J. (1996). "The genus Malassezia with description of four new species". Antonie van Leeuwenhoek. 69 (4): 337–355.
doi:
10.1007/BF00399623.
PMID8836432.
S2CID31791799.
^Maecke, Margarita (1941). "Descripción de una nueva especie de Malassezia: Malassezia ochoterenai, agente causal de Pytiriasis (Tinea) vesicolor y posición sistemática del género Malassezia". Anales del Instituto de Biología (in Spanish). 12: 511–546.
^Coutinho SD, Paula CR (June 1998). "Biotyping of Malassezia pachydermatis strains using the killer system". Rev Iberoam Micol. 15 (2): 85–7.
PMID17655416.
^Sugita T, Tajima M, Takashima M, et al. (2004). "A new yeast, Malassezia yamatoensis, isolated from a patient with seborrheic dermatitis, and its distribution in patients and healthy subjects". Microbiol. Immunol. 48 (8): 579–83.
doi:
10.1111/j.1348-0421.2004.tb03554.x.
PMID15322337.
S2CID34281815.