Skin is Home to Zoo of Bacteria

February 2007 - A new study by Martin J. Blaser, Chair of the Department of Medicine and Professor of Microbiology at NYU School of Medicine, and others, published in the online edition of the Proceedings of the National Academy of Sciences has found that human skin, the largest organ in the body, is "home to a virtual zoo of bacteria."

Led by senior research scientist Zhan Gao, MD, the research took more than three years to complete and used a powerful molecular method to sample bacteria on the forearms of six healthy subjects. Analysis identified 182 species of which 8 per cent were previously unknown.

Martin Blaser commented:

"This is essentially the first molecular study of the skin. There are probably fewer than ten labs in the US looking at this question. It is very intensive work."

This research, part of ongoing studies of human microbial ecology, found that some bacteria appeared to be effectively permanent resident on the skin; others were transient. Researchers explain that that the body has ten times more microbes than cells, with bacterial populations changing according to how we live. Maintaining population stability may contribute to health.

Researchers took swabs from three male and three female volunteers' inner right and left forearms halfway between the wrist and the elbow. Four of the individuals were retested 8 to10 months later. About half (54.4 per cent) of bacteria identified were species known to be effectively permanently resident on human skin (Propionibacteria, Corynebacteria, Staphylococcus and Streptococcus). However, the six individuals differed markedly in the overall composition of bacteria sampled with only four species in common (Propionibacterium acnes, Corynebacterium tuberculostearicum, Streptococcus mitis, and Finegoldia AB109769).

Zhan Gao said:

"This is a surprise. But many things affecting the skin affect bacteria, such as the weather, exposure to light, and cosmetics use."

The study found that 71.4 per cent of the species were unique to individual subjects, suggesting that the skin surface is highly diversified in terms of bacteria harbored. Three species were found in male subjects only (Propionibacterium granulosum, Corynebacterium singulare, and Corynebacterium appendixes). While not conclusive, researchers suggest that that there may be gender differences in the pattern of species harbored. Researchers found that bacterial populations varied over time but each individual had a core predominant set.

Martin Blaser explained:

"What that suggests is that there is a scaffold of bacteria present in everybody's skin. Some stay and others come and go."

Researchers point out that skin condition is affected by a variety of factors such as climate, diet, personal hygiene, and disease. Skin is never free of bacteria but these are not pathogenic in healthy people.

Martin Blaser added:

"Many of the bacteria of the human body are still unknown. We all live with bacteria all our lives and occasionally we smile, so they're not that bad for us."