Malassezia | |
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Malassezia furfur in skin scale from a patient with tinea versicolor | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Basidiomycota |
Subdivision: | Ustilaginomycotina |
Class: | Malasseziomycetes Denchev & T.Denchev (2014) |
Order: | Malasseziales R.T.Moore (1980) |
Family: | Malasseziaceae Denchev & R.T.Moore (2009) |
Genus: | Malassezia Baill. (1889) [1] |
Type species | |
Malassezia furfur (C.P.Robin) Baill. (1889) | |
Synonyms [2] | |
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Malassezia (formerly known as Pityrosporum) is a genus of fungi. It is the sole genus in family Malasseziaceae, which is the only family in order Malasseziales, itself the single member of class Malasseziomycetes. [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]
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. [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:
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]
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 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.
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]
Dandruff is a skin condition that mainly affects the scalp. Symptoms include flaking and sometimes mild itchiness. It can result in social or self-esteem problems. A more severe form of the condition, which includes inflammation of the skin, is known as seborrhoeic dermatitis.
Tinea versicolor is a condition characterized by a skin eruption on the trunk and proximal extremities. The majority of tinea versicolor is caused by the fungus Malassezia globosa, although Malassezia furfur is responsible for a small number of cases. These yeasts are normally found on the human skin and become troublesome only under certain conditions, such as a warm and humid environment, although the exact conditions that cause initiation of the disease process are poorly understood.
Seborrhoeic dermatitis is a long-term skin disorder. Symptoms include flaky, scaly, greasy, and occasionally itchy and inflamed skin. Areas of the skin rich in oil-producing glands are often affected including the scalp, face, and chest. It can result in social or self-esteem problems. In babies, when the scalp is primarily involved, it is called cradle cap. Seborrhoeic dermatitis of the scalp may be described in lay terms as dandruff due to the dry, flaky character of the skin. However, as dandruff may refer to any dryness or scaling of the scalp, not all dandruff is seborrhoeic dermatitis. Seborrhoeic dermatitis is sometimes inaccurately referred to as seborrhoea.
Skin disorders are among the most common health problems in dogs, and have many causes. The condition of a dog's skin and coat is also an important indicator of its general health. Skin disorders of dogs vary from acute, self-limiting problems to chronic or long-lasting problems requiring life-time treatment. Skin disorders may be primary or secondary in nature, making diagnosis complicated.
Malassezia furfur is a species of yeast that is naturally found on the skin surfaces of humans and some other mammals. It is associated with a variety of dermatological conditions caused by fungal infections, notably seborrhoeic dermatitis and tinea versicolor. As an opportunistic pathogen, it has further been associated with dandruff, malassezia folliculitis, pityriasis versicolor (alba), and malassezia intertrigo, as well as catheter-related fungemia and pneumonia in patients receiving hematopoietic transplants.
Trichosporon is a genus of anamorphic fungi in the family Trichosporonaceae. All species of Trichosporon are yeasts with no known teleomorphs. Most are typically isolated from soil, but several species occur as a natural part of the skin microbiota of humans and other animals. Proliferation of Trichosporon yeasts in the hair can lead to an unpleasant but non-serious condition known as white piedra. Trichosporon species can also cause severe opportunistic infections (trichosporonosis) in immunocompromised individuals.
Malassezia globosa is a species of yeast-like fungus.
Malassezia folliculitis or Pityrosporum folliculitis, is a skin condition caused by infection by Malassezia yeast.
Moniliella is a genus of fungi in the subdivision Ustilaginomycotina. It is in the monotypic family MoniliellaceaeQ.M. Wang, F.Y. Bai & Boekhout, which is in the monotypic order MoniliellalesQ.M. Wang, F.Y. Bai & Boekhout which is in the monotypic class MoniliellomycetesQ.M. Wang, F.Y. Bai & Boekhout.
Malassezia japonica is a fungus that can cause opportunistic infections in animals.
Malassezia dermatis is a fungus that can cause opportunistic infections in animals.
Malassezia equina is a fungus first isolated in horses, which can cause opportunistic infections in animals. Its type strain is MA146=CBS 9969. This species will not grow without any lipid supplementation. It grows slowly and forms small colonies. In the lab, colonies will not grow at temperatures of 40 °C, differing from M. sympodialis-related species, such M. dermatis and M. nana, which can grow at this temperature. Malassezia caprae cells are ovoidal.
Malassezia caprae is a fungus first isolated in goats, which can cause opportunistic infections in animals. Its type strain is MA383=CBS 10434. This species will not grow without any lipid supplementation. It grows slowly and forms small colonies. In the lab, colonies will not grow at temperatures of 40 °C, differing from M. sympodialis-related species, such M. dermatis and M. nana, which can grow at this temperature. Malassezia caprae cells are ellipsoidal to more or less spherical.
Malassezia nana is a fungus that can cause opportunistic infections in animals. It was first isolated from animals in Japan and Brazil. M. nana resembles M. dermatis and M. sympodialis, but is distinguished from these species by its inability to use Kolliphor EL (Sigma) as the sole lipid source and to hydrolyse aesculin. The type strain of M. nana is NUSV 1003T(=CBS 9557T=JCM 12085T).
Malassezia pachydermatis is a zoophilic yeast in the division Basidiomycota. It was first isolated in 1925 by Fred Weidman, and it was named pachydermatis after the original sample taken from an Indian rhinoceros with severe exfoliative dermatitis. Within the genus Malassezia, M. pachydermatis is most closely related to the species M. furfur. A commensal fungus, it can be found within the microflora of healthy mammals such as humans, cats and dogs, However, it is capable of acting as an opportunistic pathogen under special circumstances and has been seen to cause skin and ear infections, most often occurring in canines.
Malassezia sympodialis is a species in the genus Malassezia. It is characterized by a pronounced lipophily, unilateral, percurrent or sympodial budding and an irregular, corrugated cell wall ultrastructure. It is one of the most common species found on the skin of healthy and diseased individuals. It is considered to be part of the skin's normal human microbiota and begins to colonize the skin of humans shortly after birth. Malassezia sympodialis, often has a symbiotic or commensal relationship with its host, but it can act as a pathogen causing a number of different skin diseases, such as atopic dermatitis.
Trichosporon asteroides is an asexual basidiomycetous fungus first described from human skin but now mainly isolated from blood and urine. T. asteroides is a hyphal fungus with a characteristically yeast-like appearance due to the presence of slimy arthroconidia. Infections by this species usually respond to treatment with azoles and amphotericin B.
Fungal genomes are among the smallest genomes of eukaryotes. The sizes of fungal genomes range from less than 10 Mbp to hundreds of Mbp. The average genome size is approximately 37 Mbp in Ascomycota, 47 Mbp in Basidiomycota and 75 Mbp in Oomycota. The sizes and gene numbers of the smallest genomes of free-living fungi such as those of Wallemia ichthyophaga, Wallemia mellicola or Malassezia restricta are comparable to bacterial genomes. The genome of the extensively researched yeast Saccharomyces cerevisiae contains approximately 12 Mbp and was the first completely sequenced eukaryotic genome. Due to their compact size fungal genomes can be sequenced with less resources than most other eukaryotic genomes and are thus important models for research. Some fungi exist as stable haploid, diploid, or polyploid cells, others change ploidy in response to environmental conditions and aneuploidy is also observed in novel environments or during periods of stress.
Malassezia arunalokei is a species of yeast-like fungus that was identified as a new to science in 2016. It has been isolated from the skin of both seborrheic dermatitis patients and healthy individuals from India. A combination of several phenotypic characteristics distinguish this species from others in genus Malassezia. These include: colony morphology ; the absence of activity from the enzyme catalase; growth at 37 °C (99 °F); and the precipitation that results when grown with the chemicals Tween 20 or Cremophor EL.
Topical antifungaldrugs are used to treat fungal infections on the skin, scalp, nails, vagina or inside the mouth. These medications come as creams, gels, lotions, ointments, powders, shampoos, tinctures and sprays. Most antifungal drugs induce fungal cell death by destroying the cell wall of the fungus. These drugs inhibit the production of ergosterol, which is a fundamental component of the fungal cell membrane and wall.