Freeze-fracture replication of culturedPityrosporum orbiculare

Immunology of diseases associated with Malassezia species

Malassezia species are members of the human cutaneous commensal flora, in addition to causing a wide range of cutaneous and systemic diseases in suitably predisposed individuals. Studies examining cellular and humoral immune responses specific to Malassezia species in patients with Malassezia-associated diseases and healthy controls have generally been unable to define significant differences in their immune response. The use of varied antigenic preparations and strains from different Malassezia classifications may partly be responsible for this, although these problems can now be overcome by using techniques based on recent work defining some important antigens and also a new taxonomy for the genus. The finding that the genus Malassezia is immunomodulatory is important in understanding its ability to cause disease. Stimulation of the reticuloendothelial system and activation of the complement cascade contrasts with its ability to suppress cytokine release and downregulate phagocytic uptake and killing. The lipid-rich layer around the yeast appears to be pivotal in this alteration of phenotype. Defining the nonspecific immune response to Malassezia species and the way in which the organisms modulate it may well be the key to understanding how Malassezia species can exist as both commensals and pathogens.

Malassezia pachydermatis: a review

Malassezia pachydermatis is of importance in both veterinary and human medicine. Its taxonomic status and physiological characteristics are now better understood. Skin disease associated with this lipophilic yeast is now commonly recognized, especially in dogs. However, further studies are required to elucidate the mechanisms which allow this yeast to proliferate and induce disease. Skin colonization is common in pet carnivores which consequently constitute a source of M. pachydermatis for susceptible humans. In the future, the development of efficient typing systems should allow better understanding of the transmission mechanisms.

Fine structural investigation of Malassezia furfur. II. The envelope of the yeast cells

The general ultrastructure of the Malassezia furfur cell envelope is shown in a schematic model. Distinct layers such as the outer lamella, the cell wall and the plasma membrane and special structural elements of the cell wall are described and presented in electronmicrographs. Special attention was paid to the outer lamellar layer that seems to be equivalent to a capsule. It probably contains lipids as well as the cell wall, and it seems to participate in attachment processes.

Ultrastructure of budding process of Malassezia pachydermatis

The ultrastructure of Malassezia pachydermatis and its budding process was investigated by scanning and transmission electron microscopy. The innermost layer of the cell wall showed the serrated structure characteristic of the genus Malassezia. In the daughter cell, this structure became more defined as the cell grew. The mode of conidium ontogeny was monopolar blastic development with a collarette. The appearance was similar to that reported previously for Malassezia furfur, with the following difference: the budding base was 0.9-1.1 microns in diameter which was broader than that of M. furfur (0.5-0.7 microns).

Malassezia pityrosporum pachydermatis (Weidman) Dodge 1935

Priority of the name Malassezia pachydermatis (Weidman) Dodge 1935 is indicated for the microorganism which has been called Pityrosporum pachydermatis Weidman 1925 and P. canis Gustafson 1955. M. pachydermatis is here further characterized in culture with information drawn from 2 recent isolates, in particular the presence of spiral grooves on the inner surface of the cell wall, good growth on Mycosel agar, rapid production of urease, and assimilation of glucose by the Wickerham method.

FREEZE-ETCHING OBSERVATIONS OFFonsecaea pedrosoi

The fine structure of Fonsecaea pedrosoi was studied by freeze-etching techniques. The structure of the cell wall as seen in Trichophyton groups was not observed. The invaginations were clearly shown in the plasma membrane. Three-dimensional views of the fine structure were presented.