Malassezia (formerly known as Pityrosporum) is a
genus of
fungi. It is the sole genus in
familyMalasseziaceae, which is the only family in
orderMalasseziales, itself the single member of
classMalasseziomycetes.[3]Malassezia species are 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 these fungi are available. It is believed French revolutionary
Jean-Paul Marat suffered from a fungal infection from Malassezia restricta, which lead to his frequent bathing in a medicinal substance.[4]
Systematics
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 grow very slowly in
laboratory culture.[6]
Malassezia was originally identified by the French scientist
Louis-Charles Malassez in the late nineteenth century;[7] he associated it with the condition
seborrhoeic dermatitis.[8]Raymond Sabouraud identified a
dandruff-causing organism in 1904 and called it Pityrosporum Malassezii,[9] 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.[10]
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.[11]
Pityrosporum (Malassezia) pachydermatis, which is lipophilic but not lipid-dependent. It is found on the skin of most animals.
In the mid-1990s, scientists at the
Pasteur Institute in Paris, France, discovered additional species.[12]
Malassezia is the sole genus in the family Malasseziaceae, which was validated by Cvetomir Denchev and
Royall T. Moore in 2009.[13] The order Malasseziales had been previously proposed by Moore in 1980,[14] 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.[15] In 2014, Cvetomir and Teodor Denchev
circumscribed the class Malasseziomycetes to contain the group.[16]
Description
Malassezia demonstrates a rapid growth rate, typically maturing within 5 days when incubated at temperatures ranging from 30–35 °C (86–95 °F). Growth is less optimal 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.[17]
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.[17]
Species
Species Fungorum accepts 22 species of Malassezia.[18] 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.
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).[25] The skin rash of
tinea versicolor (pityriasis versicolor) is also due to infection by this fungus.
As the fungus requires
fat to grow,[12] it is most common in areas with many
sebaceous glands: on the scalp,[37] 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).
A project in 2007 sequenced the genome of dandruff-causing Malassezia globosa and found it to have 4,285 genes.[38][39]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.[37]
M. globosa has been predicted to have the ability to reproduce sexually,[40] 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.[41] Translocation of Malassezia spp. 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.[42][43]
The yeast M. restricta, normally found in the skin, is linked to disorders like
Crohn's disease and
inflammatory bowel disease when found in the gut, especially for those with the N12
CARD9 allele, which provokes a stronger inflammatory response to the yeast.[44]
^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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^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.
^Freedberg; et al., eds. (2003). Fitzpatrick's Dermatology in General Medicine (6th ed.). McGraw-Hill. p. 1187.
ISBN0-07-138067-1.
^
abGuého E, Midgley G, Guillot J (May 1996). "The genus Malassezia with description of four new species". Antonie van Leeuwenhoek. 69 (4): 337–355.
doi:
10.1007/BF00399623.
PMID8836432.
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^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.
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