The Culture Study Of Mycelial Phase Of Malassezia

Pityriasis versicolor is a chronic, relapsing, superficial fungal infection of the skin caused by the genus Malassezia. In the scales of pityriasis versicolor lesions, the mycelial phase develops whereas in artificial cultures the yeast phase predominates, and there is not easy method available for growing hyphae. In order to determine the pathogenic mechanism of mycelial phase of Malassezia, the causative agent of pityriasis versicolor, it is important to induce the hyphae development of Malassezia in vitro and to explore the requisite culture conditions.Objective: (1) to obtain an improved culture medium that could induce consistent production of hyphae of Malassezia in vitro; (2) to explore the relation between the formation of mycelial phase and culture conditions; (3) to invesigate which species of Malassezia could be induced mycelial phase; (4) to understand indirectly the nosogensis of pityriasis versicolor, through the study of transitional forms of Malassezia in vitro.Methods: The mycelial phase culture medium was preprared which consisted of yeast extract, sodium taurocholate, squalene, glycine, Tween-80 and other components. 3 standard Malassezia strains were inoculated to themycelial phase culture medium with pH 5.6, then incubated at 30°C, and the hyphae development was observed. At the same time, the scales from the lesions of the patients with pityriasis versicolor were inoculated to it. The colony and mycelial phase development were observed through macro- and microscopy. The isolates were identified to species based on the morphology and the physical and chemical characteristics.Results: ? Mycelial phase culture medium could induce some Malassezia strains (8/30) from scales of pityriasis versicolor lesions and a standard Malassezia strain to produce hyphae, but could not induce most isolated strains (22/30) and 2 standard Malassezia strains to produce hyphae; (D All of the isolates from scales of pityriasis versicolor lesions that could produce hyphae were identified as M.furfur (8/12), whereas, the isolates could not produce hyphae were identified as M.sympodialis (8/8), M.globosa (4/4), M.restricta (2/2), M.obtusa (2/2) and M.furfur (4/12). Therefore, it showed that formation of mycelial phase is related to selected Malassezia species; (3) The percentage of mycelium production of M.furfur that could produce hyphae was different. The rate of mycelium production in liquid medium (6.4%~20.6%) was higher than on solid culture medium (3.6% ~ 12.3%), by secondary culture (11.3%~23.6%) higher than by primary culture (7.9 %~ 15.5%); (4) The formation of mycelial phase was related to the composition of the mycelial phase culture medium, and squalene, sodium taurocholate, and Tween-80 were essential for hyphae development; (5) The optimal temperature for formation of mycelial phase was 30 °C; (6) pH did not significantly alter the production of mycelium in the range of pH 4.5—6.2.Conclusion: By use of the mycelial phase culture medium, we couldinduce 69.2 % of M.furfur to consistently produce hyphae in vitro, but no strains of M.sympodialis, M.globosa, M.restricta, and M.obtusa had been induced to form mycelial phase. Therefore, the conditions that could induce hyphae development in vitro not only related to the composition of the culture medium, but also related to the Malassezia species.