nd 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," says Dr. Gao. "But the more transient bacteria did change over time," she says.
"What that suggests," adds Dr. Blaser, "is that there is a scaffold of bacteria present in everybody's skin. Some stay and others come and go."
Finding the method
To obtain a sample Dr. Gao rubbed a swab on each individual's forearms. "We didn't tell them to be particularly clean, we just made sure they didn't take antibiotics up to one month prior to the test," Dr. Gao explains. She chose three men and three women to have a balance of genders. She set up a clean room so the samples didn't risk contamination.
Traditionally, bacteria are cultured in the lab in petri dishes, which contain a medium to grow bacteria. But the method leads to inaccuracies, she explains, because only a fraction of bacteria in a sample grow in that medium. So the team used a powerful molecular method that involved extracting a subunit of genetic material called 16S ribosomal DNA from the samples. "It is kind of a common currency, it's a conserved gene," says Dr. Blaser. Another advantage is that there is a large database of 16S ribosomal DNA available to scientists.
The ambitious task for this study was to gather samples, prepare them, amplify the bacteria creating colonies of each single species of bacteria present in the skin samples. Then Dr. Gao used established tools—primers—to pick out the species-specific genetic regions in the bacteria. After sequencing those regions, the 16S ribosomal DNA (rDNA) in each cPage: 1 2 3 4 5 Related medicine news :1
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