Thomas Larry Dawson

Fast, Noninvasive Method for Molecular Detection and Differentiation of Malassezia Yeast Species on Human Skin and Application of the Method to Dandruff Microbiology

ABSTRACT Malassezia fungi have been the suspected cause of dandruff for more than a century. Previously referred to as Pityrosporum ovale, Pityrosporum orbiculare, or Malassezia, these fungi are now known to consist of at least seven Malassezia species. Each species has a specific ecological niche, as well as specific biochemical and genetic characteristics. Malassezia yeasts have fastidious culture conditions and exceedingly different growth rates. Therefore, the results of surveys of Malassezia based on culture methods can be difficult to interpret. We developed a molecular technique, terminal fragment length polymorphism analysis, to more accurately survey the ecology of Malassezia yeasts without bias from culture. This technique involves fluorescent nested PCR of the intergenic transcribed spacer (ITS) ITS I and ITS II region ribosomal gene clusters. All known Malassezia species can be differentiated by unique ITS fragment lengths. We have used this technique to directly analyze scalp samples from subjects enrolled in a demographic scalp health study. Results for subjects assigned composite adherent scalp flaking scores (ASFS) <10 were compared to those for subjects assigned composite ASFS >24. Malassezia restricta and M. globosa were found to be the predominant Malassezia species present in both groups. Importantly, we found no evidence of M. furfur in either group, indicating that M. furfur can be eliminated as the causal organism for dandruff. Both groups also showed the presence of non-Malassezia fungi. This method, particularly when it is used in combination with existing fungal ITS databases, is expected to be useful in the diagnosis of multiple other fungal infections.

Hair Growth Parameters in Pre- and Postmenopausal Women

Women who undergo menopause have a cessation of ovarian estrogen production. This dramatic hormonal alteration is known to have significant effects on the skin and cutaneous appendages. As our understanding of the molecular and hormonal controls on the folliculo-sebaceous unit has grown, there has been renewed interest in the role of estrogens in modulating hair growth. Specifically, the relatively recent discovery of estrogen receptor beta has broadened and redefined prior concepts of estrogen activity and signaling. In a cohort of pre- and postmenopausal women without alopecia, a modified phototrichogram was used to measure hair density, growth rate, and percentage anagen. Optical fiber diameter analysis (OFDA) was used to determine hair diameters. Our aim was to determine whether there are any changes in hair characteristics and hair growth parameters that correlate with menopausal status. Postmenopausal women had significant changes, mainly in the frontal scalp as compared to premenopausal women. These changes included lower frontal scalp percent anagen hairs, growth rates, and hair diameters. Further study of hair changes in response to menopause provides an important opportunity for identification of treatments, targets, and strategies that may significantly benefit women.

Genomics and pathophysiology, dandruff as a paradigm

The recent sequencing of the genomes of dandruff-associated basidiomycetous yeasts, Malassezia globosa and Malassezia restricta, disclosed that the M. globosa genome is among the smallest for a free-living fungus. M. globosa produces a similar set of secreted hydrolases as the human pathogen Candida albicans. Although phylogenetically more closely related to the plant pathogen Ustilago maydis, M. globosa produces a different set of secreted hydrolases, which is a likely adaptation to the host niche and may be involved in pathogenicity. M. globosa is apparently missing several enzymes in fatty acid metabolism, including fatty acid synthase, Δ9 desaturase, and Δ2,3 enoyl CoA isomerase. The two former enzymes are apparently missing also in another skin microbe, Corynebacterium jeikeium. M. globosa has six lipase genes in each of two lipase families, which, compared with the lipases from a related fungus U. maydis, had undergone duplications since divergence from the Ustilago-containing lineage. There is also evidence for duplication of other M. globosa genes for secreted enzymes such as aspartyl proteases, phospholipases C, and acid sphingomyelinases. The M. globosa genome encodes proteins similar to all Malassezia allergens, the coding sequences of which have been isolated, and genes associated with mating, although mating has not yet been observed in Malassezia.