[Malassezia furfur septicemia after bone marrow graft]

Malassezia spp. Yeasts of Emerging Concern in Fungemia

Malassezia spp. are lipid-dependent yeasts, inhabiting the skin and mucosa of humans and animals. They are involved in a variety of skin disorders in humans and animals and may cause bloodstream infections in severely immunocompromised patients. Despite a tremendous increase in scientific knowledge of these yeasts during the last two decades, the epidemiology of Malassezia spp. related to fungemia remains largely underestimated most likely due to the difficulty in the isolation of these yeasts species due to their lipid-dependence. This review summarizes and discusses the most recent literature on Malassezia spp. infection and fungemia, its occurrence, pathogenicity mechanisms, diagnostic methods, in vitro susceptibility testing and therapeutic approaches.

The Malassezia genus in skin and systemic diseases

In the last 15 years, the genus Malassezia has been a topic of intense basic research on taxonomy, physiology, biochemistry, ecology, immunology, and metabolomics. Currently, the genus encompasses 14 species. The 1996 revision of the genus resulted in seven accepted taxa: M. furfur, M. pachydermatis, M. sympodialis, M. globosa, M. obtusa, M. restricta, and M. slooffiae. In the last decade, seven new taxa isolated from healthy and lesional human and animal skin have been accepted: M. dermatis, M. japonica, M. yamatoensis, M. nana, M. caprae, M. equina, and M. cuniculi. However, forthcoming multidisciplinary research is expected to show the etiopathological relationships between these new species and skin diseases. Hitherto, basic and clinical research has established etiological links between Malassezia yeasts, pityriasis versicolor, and sepsis of neonates and immunocompromised individuals. Their role in aggravating seborrheic dermatitis, dandruff, folliculitis, and onychomycosis, though often supported by histopathological evidence and favorable antifungal therapeutic outcomes, remains under investigation. A close association between skin and Malassezia IgE binding allergens in atopic eczema has been shown, while laboratory data support a role in psoriasis exacerbations. Finally, metabolomic research resulted in the proposal of a hypothesis on the contribution of Malassezia-synthesized aryl hydrocarbon receptor (AhR) ligands to basal cell carcinoma through UV radiation-induced carcinogenesis.

Use of fatty acid RPMI 1640 media for testing susceptibilities of eight Malassezia species to the new triazole posaconazole and to six established antifungal agents by a modified NCCLS M27-A2 microdilution method and Etest

A novel formulation of RPMI 1640 medium for susceptibility testing of Malassezia yeasts by broth microdilution (BMD) and Etest is proposed. A modification of the NCCLS M27-A2 BMD method was used to test 53 isolates of Malassezia furfur (12 isolates), M. sympodialis (8 isolates), M. slooffiae (4 isolates), M. globosa (22 isolates), M. obtusa (2 isolates), M. restricta (2 isolates), M. pachydermatis (1 isolates), and M. dermatis (2 isolates) against amphotericin B, ketoconazole, itraconazole, fluconazole, voriconazole, terbinafine, and posaconazole by BMD and Etest. RPMI and antibiotic medium 3 (AM3) were supplemented with glucose, bile salts, a mixture of fatty acids, and n-octadecanoate fatty acids and Tween 20. M. furfur ATCC 14521 and M. globosa ATCC 96807 were used as quality control strains. Depending on the species, MICs were read after 48 or 72 h of incubation at 32 degrees C. Low azole and terbinafine MICs were recorded for all Malassezia species, whereas amphotericin B displayed higher MICs (>/=16 microg/ml) against M. furfur, M. restricta, M. globosa, and M. slooffiae strains, which were AM3 confirmed. Agreement of the two methods was 84 to 97%, and intraclass correlation coefficients were statistically significant (P < 0.001). Because of higher amphotericin B MICs provided by Etest for strains also displaying high BMD MICs (>/=1 microg/ml), agreement was poorer. The proposed media are used for the first time and can support optimum growth of eight Malassezia species for recording concordant BMD and Etest MICs.

Fungal skin infections in organ transplant recipients

Transplantation is now currently and increasingly performed for the treatment of various acute and chronic diseases. Today the kidney, heart, lung, heart-lung, liver, pancreas, kidney-pancreas, small bowel and bone marrow are being transplanted. The immunological status of patients receiving such transplants exposes them to the risk of developing bacterial, viral and fungal infections. The etiological agents of mycotic diseases involving the skin of transplant recipients range from the common dermatophytes through yeasts such as Candida spp., Malassezia spp. and dimorphic fungi to the emerging molds Fusarium spp. and Pseudallescheria boydii. The very wide spectrum of fungi causing cutaneous disease produces equally varied clinical aspects. Lesions may be typical, but are very often aspecific or ambiguous. Cutaneous lesions may be the sign of a trivial mycotic disease or the marker of a disseminated, potentially lethal fungal illness, so great attention should be given to their early recognition. Cutaneous manifestations due to Candida spp., Aspergillus spp., dematiaceous fungi and Pityrosporum folliculitis are usually observed early after transplant, cryptococcosis more than 6 months later, while the frequency of dermatophytoses increases as time goes by. Coccidioides immitis, Histoplasma capsulatum and Blastomyces dermatitidis may appear any time after transplantation. The management of the more severe forms of cutaneous mycosis in transplant recipients is difficult. Besides the fact that early recognition is not easy, there are also problems regarding the effectiveness and the toxicity of the therapy and drug-drug interactions. Prophylactic measures to avoid fungal contamination must be performed during hospitalization; patients should be taught how to avoid contamination, not only during the first period after transplantation, when high dosage immunosuppressive drugs are given, but also later when a normal lifestyle is resumed.

The spectrum of Malassezia infections in the bone marrow transplant population

A consecutive series of 3044 patients who underwent BMT at the University of Minnesota over a 25 year period were reviewed for the post-transplant occurrence of infection caused by the yeast Malassezia furfur. Six patients, ranging in age from 1 to 54 years, developed Malassezia infections at a median of 59 days post transplant. Five patients were allogeneic transplant recipients; the remaining patient had undergone autologous transplantation. A spectrum of clinical manifestations of Malassezia infection was seen in these patients, including infections of mucosal surfaces and the skin, in addition to catheter-related fungemia. Unlike many of the other more common opportunistic fungal infections in immunocompromised patients, neutropenia and the use of broad-spectrum antimicrobials do not appear to be significant risk factors for Malassezia infections in the BMT population. In addition, disseminated fungal infection despite the presence of fungemia is uncommon. Lastly, the outcome of Malassezia infections in these patients, whether folliculitis, mucosal infection, or fungemia, appears to be quite favorable, in contrast to the poorer outcome with many other fungal infections in BMT patients. Catheter removal and discontinuation of intravenous lipids are important for a successful outcome in fungemic cases.

Molecular typing of Malassezia species with PFGE and RAPD

The currently recognized seven species of Malassezia all have different karyotypes which do not vary intraspecifically, except in M. furfur which displayed two different karyotypes. In contrast, random amplified polymorphic DNA (RAPD) typing showed the presence of genetic variation in all species. It is concluded that karyotype analysis is useful for species identification, and RAPD typing can be used in epidemiological investigations.