Malassezia spp.

Malassezia are fat-dependent yeasts that normally live on the skin and mucosa in humans and other mammals, including the vulva. This yeast forms a large component of the skin microbiome, being commensal but also associated with some skin problems and blood infections^​1​. Malassezia may be a commensal of the mouth and nose.

Colonisation with Malassezia species starts immediately after birth and increases until about a year of age. Colonisation is then low until just before puberty hits when sebaceous glands kick into gear and provide a better, fat-rich habitat. Malassezia then rises to a stable level. Malassezia spp. may offer a protective effect in adults by preventing colonisation of pathogenic species which are more often found in children.

Shifts in the skin microbiome occur for many reasons including environmental to genetics, lifestyle practices, personal hygiene and the individual immune system. An interesting study on the skin microbiota of Japanese Antarctic researchers and astronauts shows colonisation levels of different Malassezia species changes during stressful periods or times without bathing. Fungal diversity decreased in space while Malassezia species colonisation increased^​2,3​. Diversity decreases may indicate skin disease.

M. globosa is the most frequently identified species associated with human disease and dermatological conditions. Skin diseases are associated with Malassezia species including:

•  Pityriasis versicolor
• Malassezia folliculitis
• Seborrheic dermatitis/dandruff
• Atopic dermatitis
• Psoriasis

Antifungal susceptibility varies amongst species/genotypes. Malassezia species were formerly known as Pityrosporum.

Quick facts on Malassezia

• Genus of fungi/yeast
• Found on skin and mucosal surfaces of animals and humans
• Found on the vulva
• Can be part of healthy flora or associated with skin conditions like dermatitis and eczema
• Can cause opportunistic infections
• Can cause hypo or hyperpigmentation on human skin
• Allergy testing can detect this species
• Causes pityrosporum folliculitis
• Very slow to grow in lab, fastidious grower, hard to culture but can be found using DNA detection methods
• Causes dandruff, seborrhoeic dermatitis
• May be found in breast milk, gut, mouth, blood, urine, the lungs and vagina

Diseases in humans

Malassezia species that cause the most skin problems in humans is the M. globosa, and to a lesser degree, M. restricta. Tinea versicolour is caused by Pityriasis versicolour, also the Malassezia family.

The fungus typically requires fat to grow, so it does so in those areas where there are sebaceous (oil) glands: scalp, face, upper body, and may also occur in the groin and possibly even on the vulva. ^​1​

When the fungus grows quickly, cell renewal is interrupted and dandruff – flaking skin cells – appear, along with itching. There may be up to 10 million species of M. globosa on the human head.

Malassezia may also cause some pancreatic cancers when it travels from the gut lumen to the pancreas. May cause gut inflammation.^​4​

M. furfur has been identified in deep infections of the blood, urine and vagina, and is associated with immune compromised patients in hospitals. This infection has also been found in septicemia in newborns receiving fat supplementation via catheters.

17 Malasseziomycetes exist:

• Pityrosporum (Malassezia) ovale – fat-dependent, found only in humans, divided into P. ovale and P. orbiculare, but M. furfur is preferred
• Pityrosporum (Malassezia) pachydermatis – lipophilic (attracted to fats) but not reliant on fats, found on skin of most animals
• M. caprae
• M. cuniculi
• M. dermatis
• M. equina
• M. furfur
• M. globosa
• M. japonica
• M. nana
• M. obtusa
• M. pachydermatis
• M. restricta
• M. slooffiae
• M. sympodialis
• M. yamatoensis
• M. psittaci

References