Your skin is home to thousands of types of bacteria, and the ways in which they contribute to healthy skin are still largely a mystery. This mystery can become even more complex: in an article published Thursday in the journal Cell Host & Microbe, researchers studying the many varieties of Cutibacterium acnes bacteria in 16 human volunteers found that each pore was a world on its own. Each pore contained only one type of C. acnes.
C. acnes occurs naturally and is the most abundant bacteria on the skin. Its link to acne, the skin disease, is unclear, said Tami Lieberman, a professor at MIT and author of the new article. If biologists are to uncover the relationship between the inhabitants of your face and its health, this will be an important step in understanding whether different strains of C. acnes have their own talents or niches, and how the strains are distributed on your skin.
To collect their samples, Dr. Lieberman and his colleagues used commercially available nasal strips and old-fashioned compression with a tool called a comedone extractor. They then spread samples, each much like a microscopic ice core, from the pores of the Petri dishes. They did the same with toothpick samples rubbed on the surface of participants’ foreheads, cheeks and backs, which picked up 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 exhibited a unique combination of strains, but what surprised the researchers most was that each pore harbored a single variety of C. acnes. The pores were also different from their neighbors – there was no clear pattern uniting the pores on the left cheek or forehead across the volunteers, for example.
Moreover, judging from the sequencing data, the bacteria present in each pore were essentially identical.
“There is tremendous diversity in a square inch of your face,” said Arolyn Conwill, postdoctoral researcher and lead author of the study. “But in just one of your pores there is a complete lack of diversity.”
What scientists believe is that each pore contains the descendants of a single individual. The pores are narrow, deep recesses with oil-secreting glands at the bottom, Dr. Lieberman said. If a C. acnes cell does manage to enter it, it can proliferate until it fills the pore with copies of itself.
It would also explain why strains that don’t grow very fast manage to avoid being competed with by faster strains on the same person. They don’t compete with each other; they live side by side in their own walled gardens.
Oddly enough, these gardens are not very old, scientists believe. They estimate that the founding cells of the pores they studied did not take up residence until about a year ago.
What happened to the bacteria that lived there before? Researchers don’t know – perhaps they were destroyed by the immune system, fell prey to viruses, or were ripped off unceremoniously by a nasal strip, paving the way for new founders.
Dr Lieberman said the discovery had implications for microbiome research more broadly. For example, a simple swab of someone’s skin would never hint at the complexity discovered in this study. And as scientists contemplate the possibility of manipulating our microbiomes to help treat disease, the patterns uncovered in this study imply the need for information about the location and disposition of microbes, not just their identity. In the future, if doctors are hoping to replace someone’s current skin inhabitants with others, they may need to clean their pores first.
And could it be that another inhabitant on our faces is playing a role in how bacteria in each pore come and go?
âWe have mites on our faces that live in the pores and eat bacteria,â Dr. Lieberman said. What role do they play in this ecosystem, with regard to the maintenance of C. acnes gardens, has yet to be determined.