MalaSelect: A Selective Culture Medium for Malassezia Species

Abstract

Malassezia species are fastidious and slow-growing yeasts in which isolation from polymicrobial samples is hampered by fast-growing microorganisms. Malassezia selective culture media are needed. Although cycloheximide is often used, some fungi, including the chief human commensal Candida albicans, are resistant to this compound. This study aimed to test whether the macrolide rapamycin could be used in combination with cycloheximide to develop a Malassezia-selective culture medium. Rapamycin susceptibility testing was performed via microdilution assays in modified Dixon against two M. furfur and five Candida spp. The MIC was the lowest concentration that reduced growth by a minimum of 90%. Rapamycin ± cycloheximide 500 mg/L was also added to FastFung solid, and yeast suspensions were inoculated and incubated for 72 h. Rapamycin MICs for Candida spp. ranged from 0.5 to 2 mg/L, except for C. krusei, for which the MIC was > 32 mg/L. M. furfur stains were rapamycin-resistant. Rapamycin and cycloheximide supplementation of the FastFung medium effectively inhibited the growth of non-Malassezia yeast, including cycloheximide-resistant C. albicans and C. tropicalis. Based on our findings, this “MalaSelect” medium should be further evaluated on polymicrobial samples for Malassezia isolation and culture.

Lesional skin of seborrheic dermatitis patients is characterized by skin barrier dysfunction and correlating alterations in the stratum corneum ceramide composition

“…Although it is hypothesised that specific Malassezia species might be responsible for instigating inflammation as virulence factors differ between Malassezia species, 41–43 no significant differences on species level were observed in this study. Culturing led to successful isolation of Malassezia species in approximately half of the subjects, illustrating the known challenges of isolating Malassezia from clinical samples 44 . Except for M. slooffiae , all species are relatively frequently isolated from healthy and SD skin 45 .…”

“…Culturing led to successful isolation of Malassezia species in approximately half of the subjects, illustrating the known challenges of isolating Malassezia from clinical samples. 44 Except for M. slooffiae, all species are relatively frequently isolated from healthy and SD skin. 45 Remarkably, M. slooffiae has been reported to have little virulence when directly compared to M. globosa and M. sympodialis.…”

Differential lipase virulence in Malassezia furfur dimorphism isolated from pityriasis versicolor patients and healthy individuals

“…However, the conditions required to produce mycelial formation by Malassezia yeasts is not well characterised, and investigators have proposed that morphological changes require in vivo conditions 10 . Indeed, several studies have attempted to stimulate morphological change of M. furfur in vitro by varying culture conditions with variable success 11–13 …”

“…10 Indeed, several studies have attempted to stimulate morphological change of M. furfur in vitro by varying culture conditions with variable success. [11][12][13] Lipids are a major factor in regulating the effective growth of Malassezia as all species of Malassezia require exogenous lipids for their growth. 1,14,15 The cell walls of Malassezia mainly consist of lipids, and these compounds influence their pathogenicity.…”