There is a reason why we wash our hands before meals. From a photo of microbes on a child's hand, we can see how many bacteria we carry every day. American microbiologist Tasha asked her eight-year-old son to print a handprint when he came back from playing outside. Then, she put this handprint on agar for 48 hours.

The picture below is a recent photo of the largest colony, which may be Bacillus, a rod-shaped bacterium common in hands. To find out which microorganisms are, more detailed tests are needed. The white colony may be a staphylococci. About 30% people have staphylococci in their nasal cavity, so they generally don't get sick. However, some staphylococci may cause diseases after developing antibiotic resistance.

Among them, colonies composed of yeast and fungi will show their true colors only when they grow at room temperature. It is easy to forget that our bodies are home to millions of bacteria and microorganisms-most of them are harmless. In fact, the bacterial species contained in the fingerprint in this Petri dish may even help the human immune system.

The picture below shows the unknown colony outside the fingerprint, which may be caused by the pollution of the Petri dish. Researchers believe that there may be more microbes in us than human cells. When we move from one house to another, we will "occupy" the new residence with all the bacteria in just one hour. These bacteria have unique characteristics and can be used to solve crimes in the future.

(compile: leaves)