Your skin is home to thousands of types of bacteria and the way they contribute to healthy skin is still largely mysterious. This mystery can be even more complicated: In an article published Thursday in Cell Host & Microbe, researchers studying many species of Cutibacterium acnes in 16 human volunteers found that each pore is a world to itself. Each pore contained only one type of C. acnes.
C. acnes occurs naturally and is the most abundant bacterium on the skin. Its connection to acne, a skin condition, is not clear, said Tami Lieberman, a professor at MIT and author of a new article. If biologists want to unravel the relationship between your facial population and their health, this will be an important step in understanding whether different strains of C. acnes have their own abilities or niches and how the strains are distributed across the skin.
For sampling Dr. Lieberman and colleagues used commercially available nasal strips and old-fashioned squeezing using a tool called a comedone extractor. Then they smeared the samples, each a bit like a microscopic ice core, from the pores on Petri dishes. The same was done with samples of toothpicks spread on the surface of the participants’ foreheads, faces and backs, which captured bacteria living on the surface of the skin rather than in the pores. They let the bacteria grow, then sequenced their DNA to identify them.
Each person’s skin had a unique combination of strains, but what surprised the researchers the most was that each pore contained a single variety of C. acnes. The pores were also different from their neighbors – for example, there was no clear pattern in volunteers connecting the pores of the left face or forehead.
What’s more, judging by the sequencing data, the bacteria in each pore were essentially identical.
“There’s a huge amount of diversity per square centimeter of your face,” said Arolyn Conwill, a postdoctoral researcher who is the lead author of the study. “But there is a complete lack of diversity in one of your pores.”
Scientists think that it happens that each pore contains the offspring of one individual. The pores are deep, narrow cracks with oil-secreting glands at the bottom, said Dr. Lieberman. If a C. acnes cell manages to get down there, it can multiply until it fills the pores with its copies.
This would also explain why strains that do not grow too fast avoid competition from faster strains on the same person. They don’t compete with each other; they live side by side in their walled gardens.
Interestingly, these gardens are not very old, scientists think. They estimate that the basal cells in the pores they studied settled only about a year ago.
What happened to the bacteria that used to live there? Scientists do not know this – they may have been destroyed by the immune system, they may have fallen victim to viruses, or they may have been ripped off by a strip of nose and cleared the way for new founders.
Dr. Lieberman said the finding has a broader impact on microbiome research. For example, a simple swab from one’s skin would never indicate the complexity revealed in this study. And because scientists are considering manipulating our microbiomes to help treat disease, the patterns revealed in this study imply a need for information about the location and arrangement of microbes, not just their identity. In the future, if doctors hope to replace one’s current skin with others, they may need to clean their pores first.
And could it happen that another inhabitant on our faces plays a role in how the bacteria in each pore come and go?
“We have mites on our faces that live in pores and eat bacteria,” said Dr. Lieberman. What role do they play in this ecosystem when it comes to maintaining C. acnes gardens, has yet to be determined.