Human skin harbors completely unknown bacteria

The first study to identify the composition of bacterial populations on the skin using a powerful molecular method. Not only were the bacteria more diverse than previously estimated, but some of them had not been found before,” stated Dr Martin J Blaser, Frederick King Professor and Chair of the Department of Medicine and Professor of Microbiology at New York University (NYU) School of Medicine.
According to Dr Blaser and his team, the skin, the largest organ in the human body, is a kind of zoo and some of the inhabitants are quite novel. Researchers in their study found evidence for 182 species of bacteria in skin samples. Eight percent were unknown species that had never before been described.
"The skin is home to a virtual zoo of bacteria," stated Dr Blaser. This study was published on February 5, 2007, in the online edition of the Proceedings of the National Academy of Sciences.
The researchers analyzed the bacteria on the forearms of six healthy subjects, three men and three women. According to Dr Blaser, this is essentially the first molecular study of the skin. He explained that the skin has been a terra incognita, an unknown world that he and his colleagues have set out to understand much like explorers.
In the new study, the researchers took swabs from the inner right and left forearms of six individuals picking the region halfway between the wrist and the elbow for its convenience. It is not where they wash their hands or undress. The researchers wanted to be able to compare two similar parts of the body. Because they also wanted to study change over time, they took swabs from four of the individuals eight to10 months after the first test.
The team used a powerful molecular method that involved extracting a subunit of genetic material called 16S ribosomal DNA from the samples to characterize the bacteria.
Roughly half, or 54.4 perecnt, of the bacteria identified in the samples represented the genera Propionibacteria, Corynebacteria, Staphylococcus and Streptococcus, which have long been considered more or less permanent residents in human skin.
The six individuals differed markedly in the overall composition of the bacterial populations on their skin. They only had four species of bacteria in common: Propionibacterium acnes, Corynebacterium tuberculostearicum, Streptococcus mitis and Finegoldia AB109769. “This is a surprise,” exclaimed Dr Gao. “But many things affecting the skin affect bacteria, such as the weather, exposure to light, and cosmetics use.”
Almost three-quarters, or 71.4 percent, of the total number of bacterial species were unique to individual subjects, suggesting that the skin surface is highly diversified in terms of the bacteria it harbors, according to the study. Three bacterial species were only found in the male subjects: Propionibacterium granulosum, Corynebacterium singulare, and Corynebacterium appendixes. While the sample is too small to draw conclusions, the scientists believe that women and men may harbor some different bacterial species on their skin.
In each individual, the bacterial populations varied over time while revealing a core set of bacteria for each individual. “The predominant bacteria don't change much,” said Dr Gao. “But the more transient bacteria did change over time.” “That suggests that there is a scaffold of bacteria present in everybody's skin. Some stay and others come and go, added Dr Gao.”
The next step for the research team is to look at diseased skin. “We plan to ask the question: Are the microbes in diseased skin, in certain diseases like psoriasis or eczema, different than the microbes in normal skin?” stated Dr Blaser.