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Researchers at the National Institutes of Health, the National Human Genome Research Institute (NHGRI) and the National Cancer Institute (NCI) have published a report on microbes in the skin that they hope will help to prevent skin diseases. In a report featured in Science, researchers studied the DNA of all microbes that inhabit human skin and found that human skin holds a larger variety of bacteria than previously thought.
The researchers studied skin's microbes with modern DNA sequencing technology and computational analysis. They took skin samples from 20 skin sites predisposed to certain dermatological disorders on the bodies of 10 healthy volunteers. They then extracted DNA from each sample and sequenced the 16S ribosomal RNA genes, a type of gene that is specific to bacteria. The researchers identified more than 112,000 bacterial gene sequences, which they then classified and compared. The analysis detected bacteria belonging to 19 different phyla and 205 different genera, with diversity at the species level being much greater than expected.
The study also showed that in healthy individuals, the greatest influence on bacterial diversity appeared to be body location. For example, the bacteria that live in a person's underarm area are more likely to be similar to those in the underarm area of another person than they are to the bacteria on the same person's forearm.
The skin sites selected for the study represented three microenvironments: oily, moist and dry. The oily sites were between the eyebrows, beside the nose, inside the ear, in the back of the scalp, and on the upper chest and back. Moist areas were inside the: nose, armpit, inner elbow, webbed area between the fingers, groin area and top fold of the buttocks; behind the knee, bottom of the foot and the navel. Dry areas included the inside surface of the mid-forearm, the palm of the hand and the buttock.
Researchers found that dry and moist skin had a broader variety of microbes than did oily skin. Oily skin contained the most uniform mix of microbes. To look for changes that may occur in the skin microbiome over time, the researchers sampled some volunteers twice, taking samples about four to six months apart. Most of the re-sampled volunteers were found to more like themselves over time than they were like other volunteers. However, the stability of the microbial community was dependent on the site surveyed. The greatest stability was found in samples from inside the ear and nose, and the least stability was found in samples from behind the knee.