Senior Scholar Award in Global Infectious Disease
Martin J. Blaser, M.D.
New York University School of Medicine

Molecular definition of the bacterial population of human skin in health and disease

The human body is colonized by bacteria from birth through death. These bacteria live on and in us, colonizing the upper respiratory tract, the gastrointestinal tract, the genital tract, and the skin. In total, we carry many more bacterial cells than we carry human cells.

It has long been appreciated that the human skin is colonized by a variety of microbes. Some of these can grow in culture whereas others can be seen but not grown. Thus, the microbes that constitute the skin “flora” have not been well-defined. Our hypothesis is that, as with other parts of the body, the bacteria that can be cultured represent only a fraction of the total population.

We plan to use molecular methods to define the organisms present in human skin. This work is facilitated by the presence of a highly conserved molecule called 16S rRNA. This molecule is central to the ability of bacterial cells to make proteins, and thus is present in all cells. A molecular technique, known as PCR (polymerase chain reaction), can be used to amplify very small amounts of 16S rRNA in a specimen, enabling its detection.

Marrying 16s rRNA technology and PCR would allow detection and identification of the bacteria normally present in skin. We plan to inventory the organisms present in several healthy individuals. We will use a bioinformatic approach to determine which species are present, and to test their distribution according to anatomical site, and whether they are host-specific. After a survey of the organisms present in healthy skin, for example, focusing on the forearm, we will begin to study specimens from patients with skin diseases.

Our hypotheses are as follows:

1. There will be a generally conserved population of bacteria in most or all people.

2. Individual differences will occur in healthy persons. Transient bacterial populations likely will be identified as well.

3. Bacterial populations in diseased skin will differ from those in normal skin, even in the same host. Such differences may be used to develop tests to specifically diagnose the presence of the organism, and thus, the disease.

4. The bacterial differences may relate to the causation of these conditions. In other words, identifying a microbe as frequently or always colonizing diseased tissue in several hosts, may be a clue as to its role as an infecting agent. Such observations could lead to new approaches to diagnosis, prevention, and treatment of skin diseases.

Contact Dr. Blaser.