Malassezia pachydermatis and other Malassezia species: Antifungal Susceptibility Tests.

Information 08-16-2011.

The Malassezia includes 13 species: Malassezia pachydermatis, M. furfur, M. sympodialis, Malassezia globosa, M. obtuse, M. restricta, M. slooffiae, M. dermatis, M. japonica, M. yamatoensis, M. nana, M. and M. caprae equine.

Yeasts Malassezia are part of the normal microbiota of the external ear, and has also been found in the skin, rectum, anus, vagina and dogs and cats. They act as opportunistic pathogens of skin and ear of small animals, M. pachydermatis being the most common and is often implicated in otitis externa dogs. Malassezia dermatitis is one of the most common skin infections in dogs. M. pachydermatis yeast is a lipophilic, non lipid-dependent, commensal skin animals which can be pathogenic under the influence of factors causing malasseziosis boxes. Among these predisposing factors include: alterations defense mechanisms, changes in environment such as excessive wax production after antibiotic therapy or corticosteroids, food hypersensitivity, flea bites and / or atopy, pyoderma, demodicosis, or endocrine problems (hyperadrenocorticism, hyperthyroidism, diabetes mellitus). Clinical manifestations include otitis externa and various forms of dermatitis in pets. In addition, nosocomial infections have been reported in humans, including in intensive care units. These cases have been attributed to the zoonotic transmission from a pet colonized hands of health personnel, and subsequent transmission person-person through contact.

Since 2002, the National Committee for Clinical Laboratory Standard Institute (now Clinical Laboratory Standard Institute -CLSI-) approved a method of micro- and Macrodilution for susceptibility testing yeast with RPMI 1640 medium (NCCLS M27) which is applicable to yeast Cryptococcus and Candida species. This method was later used for Malassezia pachydermatis, being a non - lipid - dependent yeast, but some consider inappropriate for Malassezia by their lipophilicity. We used several liquid media as Christensen urea broth supplemented with 0.1% Tween 80 and 0.5% tween 40; modified RPMI 1640 medium containing lipids (2% glucose, 0.4% Oxgall 0.1% glycerol, 0.05% glycerol monostearate, 0.05% Tween 20), Sabouraud Dextrose broth with 1% tween 80 (SDB-T 80), or modified Dixon broth (3.6% malt extract, 0.6% peptone, 2.0% ox bile, 1.0% tween 40; 0 , 2% glycerol, 0.2% oleic acid, pH 6.0), among others. Upon comparative studies it seems Sabouraud dextrose broth to 1% tween 80 appears to be most appropriate for a good growth. The incubation period recommended is 48 to 72 hours at 32C.

Azole antifungals (miconazole, ketoconazole, itraconazole, ...) are used by typical or systemically to treat skin infections is located M. pachydermatis. It has also been recommended thiabendazole, including its association with neomycin and dexamethasone antifungal, antibacterial and anti-inflammatory activity. Sensitivity tests are necessary for having described azole resistant strains. For cases of human systemic infections, Amphotericin B is recommended because it has been shown in vitro sensitive.

Tests in IVAMI

  • Antifungal susceptibility testing of any species of Malassezia pachydermatis including Malassezia.