Monday, 27 May 2013

Human Skin Fungal Diversity

The National Institutes of Health researchers have sequenced the DNA of fungi at skin sites of healthy adults to define the normal populations across the skin and to provide a framework for investigating fungal skin conditions. Fungi, along with bacteria, form part of the human skin microbiome.

The researchers collected samples at 14 body sites from 10 healthy adults. DNA sequencing of the fungi in the samples identified fragments of DNA, called phylogenetic markers, which can be counted and used to distinguish one type of fungus from another. The sequencing efforts generated more than 5 million markers, from the samples, representing more than 80 fungal types, or genera.

The researchers identified fungi from two phyla, Ascomycetes and Basidiomycetes, as part of the normal fungal census at the 14 skin sites. The researchers found that a single type of fungus, belonging to the genus Malassezia, is predominant on the head and trunk. Hands, which harbor a great diversity of bacteria, are home for relatively few types of fungi. In contrast, feet, including toenails, heels and toe webs contain tremendous diversity.

The most common types of fungi were:

Malassezia spp. 62 isolated, including:

Malassezia globosa
Malassezia restricta
Malassezia sympodialis

Pencillium spp. 25 isolated, including:

Pencillium chyrsogenum
Pencillium lanosum

Aspergillus spp. 19 isolated, including:

Aspergillus candidus
Aspergillus terreus
Aspergillus vesicolor

Less than 5 isolated of each of the following:

Alternaria spp.
Candida spp.
Chaetomium spp.
Chryssoporium spp.
Cladosporium spp.
Mucor spp.
Rhodotorula spp.
Tricophyton spp.

The most complex site, the heel, is home to about 80 genus-level types of fungi. The researchers found about 60 types in toenail swab samples and 40 types in samples from the webs of the toes. Sites with moderate fungal diversity are inside the bend of the arm, inside of the forearm and palm, with each location supporting 18 to 32 genera of fungi. The head and trunk body sites, including the back, back of the neck, inside the ears, behind the ears, and between the eyebrows, have far fewer fungi types, with just two to 10 genera each.

The research team compared fungal diversity data with the skin bacteria on the same healthy adults. They found that while arms have high measures of bacterial diversity, they have lower fungal diversity. They found the reverse to be true for sites on the feet. Core body sites had neither a high bacterial diversity nor a high fungal diversity. The researchers had previously shown that bacterial diversity can be predicted by whether skin is moist, dry or oily. Fungal diversity, instead, seems to depend upon where a particular skin site is on the body.

The new study appears in an online issue of Nature. The paper is titled “Topographic diversity of fungal and bacterial communities in human skin.”

Keisha Findley, Julia Oh, Joy Yang, Sean Conlan, Clayton Deming, Jennifer A. Meyer, Deborah Schoenfeld, Effie Nomicos, Morgan Park, Heidi H. Kong, & Julia A. Segre1 (2013): Topographic diversity of fungal and bacterial communities in human skin, Nature, 498,367–370 doi:10.1038/nature12171

Posted by Tim Sandle