''Malassezia pachydermatis'' is a zoophilic

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

in the division

Basidiomycota Basidiomycota () is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basi ...

. It was first isolated in 1925 by Fred Weidman, and it was named ''pachydermatis'' (Greek for 'thick-skin') after the original sample taken from an

Indian rhinoceros } The Indian rhinoceros (''Rhinoceros unicornis''), also called the Indian rhino, greater one-horned rhinoceros or great Indian rhinoceros, is a rhinoceros species native to the Indian subcontinent. It is listed as Vulnerable on the IUCN Red Li ...

(''Rhinocerosus unicornis'') with severe exfoliative dermatitis. Within the genus ''

Malassezia ''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. ''Malassezia'' species ...

'', ''M. pachydermatis'' is most closely related to the species '' M. furfur''. A

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

, it can be found within the

microflora Microbiota are the range of microorganisms that may be commensal, symbiotic, or pathogenic found in and on all multicellular organisms, including plants. Microbiota include bacteria, archaea, protists, fungi, and viruses, and have been found to ...

of healthy mammals such as humans, cats and dogs, However, it is capable of acting as an

opportunistic pathogen An opportunistic infection is an infection caused by pathogens (bacteria, fungi, parasites or viruses) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune ...

under special circumstances and has been seen to cause skin and ear infections, most often occurring in canines.

Description

''Malassezia pachydermatis'' is a bottle-shaped, non-lipid dependent

lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipop ...

yeast in the genus ''

''. Colonies are cream or yellowish in colour, smooth to wrinkled and convex with a margin possessing a slightly lobed appearance. Cells are ovoidal in shape and range in size from 3.0–6.5 x 2.5 μm. Colonies grow via unipolar budding, and

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e are rarely seen in culture. Optimal growth occurs at with maturation occurring in five days. It is the only species of ''

'' capable of growing without the presence of

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

s. Although it is not lipid-dependent, its growth is enhanced by the presence of lipids. Its DNA is characterized by a 56%

guanine-cytosine content In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out ...

Pathogenicity

Within infected tissues, this yeast produces several enzymes such as

proteinase A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...

phospholipase A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. Acids trigger the release of bound calcium from cellular stores and the consequent increase in free cytosolic Ca2+, an essential step in ...

hyaluronidase Hyaluronidases are a family of enzymes that catalyse the degradation of hyaluronic acid (HA). Karl Meyer classified these enzymes in 1971, into three distinct groups, a scheme based on the enzyme reaction products. The three main types of hyal ...

and chondroitin-sulphatase.

Proteinase A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...

and

are also released in infections involving ''

Candida albicans ''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is us ...

'' and have been found to contribute to its virulence by inducing pores into host cell membranes, which eventually lead to their loss of function. For this reason it has been suggested that these enzymes may also serve a function in the pathogenicity of ''M. pachydermatis''. However, pathogenicity in this species has yet to be associated with any specific genotypic and phenotypic traits. ''Malassezia pachydermatis'' in its pathogenic form can be found colonizing a variety of animals such as

rhinoceros A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species o ...

es,

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

black bear Black bear or Blackbear may refer to: Animals * American black bear (''Ursus americanus''), a North American bear species * Asian black bear (''Ursus thibetanus''), an Asian bear species Music * Black Bear (band), a Canadian First Nations group ...

s and domesticated

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s. It is however most commonly associated with canine ear and skin infections.

Canine infection

''Malessezia pachydermatis'' is an important pathogen in veterinary medicine. It has been known to become pathogenic to its host causing

otitis Otitis is a general term for inflammation or infection, inner ear infection, middle ear infection of the ear, in both humans and other animals. When infection is present, it may be viral or bacterial. When inflammation is present due to fluid buil ...

and

seborrhoeic dermatitis Seborrhoeic dermatitis, sometimes inaccurately referred to as seborrhoea, is a long-term skin disorder. Symptoms include red, scaly, greasy, itchy, and inflamed skin. Areas of the skin rich in oil-producing glands are often affected including the ...

. First associated with canine

otitis externa Otitis externa, also called swimmer's ear, is inflammation of the ear canal. It often presents with ear pain, swelling of the ear canal, and occasionally decreased hearing. Typically there is pain with movement of the outer ear. A high fever is ...

in 1955 by Benght A. Gustafson, this yeast has since become an important pathogen especially in the study of small animal medicine. Symptoms include excessive scratching, head shaking, odour, and reddish-brown waxy deposits within the ear canal. ''Malassezia pachydermatis'' caused canine

was first discovered by Dufait in 1975 and may be characterized by symptoms ranging from dandruff to scaly lesions. At infection sites sebaceous secretions are increased. Differences to susceptibility can be seen across breeds for example, increased infection among the

West Highland White Terrier The West Highland White Terrier, commonly known as the Westie, is a breed of dog from Scotland with a distinctive white harsh coat with a somewhat soft white undercoat. It is a medium-sized terrier, although with longer legs than other Scott ...

has been attributed to a genetic abnormality. Low pH environments have been associated with antimicrobial activity and dogs have among the highest skin pH levels of any domesticated animal. ''Malassezia pachydermatis'' is most commonly isolated from areas of the skin and ears with higher pH levels. Therefore canine colonization may occur more readily due to the skins increased alkalinity. Samples have been collected from the ears, skin, vagina, and anal sacs. Canine infection often co-occurs with atopy and other allergic disorders. In contrast, felines are rarely infected by ''M. pachydermatis'' but when ''Malassezia'' spp.

dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can v ...

does occur, it is not typically associated with any other conditions.

Human infection

Infections are relatively rare in humans, with some studies reporting only about 2% prevalence on individuals with

. In terms of non-infectious occurrence, the same study found it on less than 1% of healthy populations. This yeast has been isolated from a number of areas of the human body such as the blood, lungs, eyes, ears, skin and genitals. The number of human infections is not clear and it is possible that they are only transient, with humans (often pet owners) acting as carriers. Infections are most often found on premature or IV-fed neonates as well as immunocompromised adults. Premature or IV-fed neonates seem to be particularly susceptible to infection. These low-birthweight infants are routinely fed lipid solutions from

arterial catheter An arterial line (also art-line or a-line) is a thin catheter inserted into an artery. Use Arterial lines are most commonly used in intensive care medicine and anesthesia to monitor blood pressure directly and in real-time (rather than by i ...

s but these lines may be colonised by ''M.pachydermatis'', in turn causing bloodstream infections called

fungemia Fungemia is the presence of fungi or yeasts in the blood. The most common type, also known as candidemia, candedemia, or systemic candidiasis, is caused by '' Candida'' species; candidemia is also among the most common bloodstream infections of a ...

. Initial exposure in these intensive care nurseries have been attributed to pet-owning health care workers who act as vectors for the fungus.

Detection

''Malassezia pachydermatis'' can be distinguished from other species in the genus by its ability to grow on

Sabouraud agar Sabouraud agar or Sabouraud dextrose agar (SDA) is a type of agar growth medium containing peptones. It is used to cultivate dermatophytes and other types of fungi, and can also grow filamentous bacteria such as '' Nocardia''. It has utility ...

. Cotton ear swabs, adhesive tape methods, skin scrapings, and biopsy can be used to collect samples that are analysed via

microscopy Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of micr ...

or culturing techniques, however, under-diagnoses may occur due to an increase in the number of days culture may require to develop and discrepancies in laboratory techniques. While ''M. pachydermatis'' is routinely detected by swabbing of external areas of canine ears, its presence within the deeper portions of the ear canal is associated with infection.

Treatment

Antifungal medications such as

imidazole Imidazole (ImH) is an organic compound with the formula C3N2H4. It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. In chemistry, it is an aromatic heterocycle, classified as a diazole Diazole refers ...

nystatin Nystatin, sold under the brandname Mycostatin among others, is an antifungal medication. It is used to treat '' Candida'' infections of the skin including diaper rash, thrush, esophageal candidiasis, and vaginal yeast infections. It may also be ...

and

natamycin Natamycin, also known as pimaricin, is an antifungal medication used to treat fungal infections around the eye. This includes infections of the eyelids, conjunctiva, and cornea. It is used as eyedrops. Natamycin is also used in the food indust ...

may be used to treat infections. The former functions by weakening the fungal cell wall, while the latter two disrupt permeability of the plasma membrane. In canine infection causing

the ear canal may be cleaned using an ear cleansing solution often paired with the removal of surrounding hair. Separation of biotypes as well as treatment has proven successful using killer yeast strains such as ''

Pichia ''Pichia'' (''Hansenula'' and ''Hyphopichia'' are obsolete synonyms) is a genus of yeasts in the family Pichiaceae with spherical, elliptical, or oblong acuminate cells. ''Pichia'' is a teleomorph, and forms hat-shaped, hemispherical, or round asc ...

anomala''. In these studies by Coutinho ''et al.'', ''M. pachydermatis'' was isolated from canine skin swabs and otic secretions which were then exposed to toxin producing killer yeast strains that inhibited ''M. pachydermatis'' growth.

References

{{Taxonbar, from=Q10575745 Basidiomycota Fungi described in 1925