This article is an updated 2026 version of the popular 50-part Japanese series “Microorganisms, Too Embarrassed to Ask Others About!” (いまさら人には聞けない！微生物のお話), previously published on GMP Platform*.
Over the next several installments, I will explore a wide range of topics related to microorganisms, from the fundamentals to more in-depth insights that are not widely known even among professionals in the field.
Previously…
– Fundamentals of Microbiology [Part 1]
We Live Surrounded by Microorganisms
Individual microorganisms are very small and cannot be seen with the naked eye, so we rarely are aware of their existence in daily life. However, unless in a highly controlled environment, microorganisms should be considered to exist everywhere around us. In the air, water, sea, soil, on office desks, on the surface of the skin and mucous membranes, and even in the deep sea, stratosphere, desert sand… Microorganisms exist in almost all conceivable environments.As in the recent news that a large number of microorganisms found in meters underground, microorganisms can exist in places where ordinary animals and plants cannot survive.
It is said that there are 1030 bacteria living on Earth, far more than the number of stars in the entire universe, and their weight (in terms of carbon content) is equivalent to the total of all plants on Earth. (https://yusukeokazaki.weebly.com/basic_info.html)
It is also said that there are more than 100 trillion microorganisms (mainly bacteria) in our bodies. This is far more than the number of cells (about 37 trillion) that make up the human body. (Source: Hygienic Microbiology Research Center website)
Despite this surprising number, these microorganisms are not evenly distributed throughout the body. Microorganisms mainly exist on the body surface and in the digestive tract including the oral cavity. It is said that there are thousands to tens of thousands of microorganisms per 1 cm² on the skin of a healthy person. Inside the digestive tract (which is in contact with the outside world through the mouth and anus), there are a large number of bacteria called intestinal bacteria. A huge number of microorganisms also inhabit dental plaque in the oral cavity. On the other hand, in healthy people, the inside of the body excluding the digestive tract (blood, body fluids, muscles, bones, brain, etc.) is basically sterile.
So, are there any places on Earth where microorganisms do not exist?
A familiar example is fire. No life known to us exists in fire. Similarly, actively active volcanic craters, the interior of blast furnaces, the interior of nuclear reactors, etc. are likely to be sterile. What about cleanrooms? A properly maintained and managed cleanroom should maintain a sterile state. However, since workers and various items enter and exit, regular decontamination and strict daily management are necessary to maintain sterility.
On the other hand, from the opposite perspective, the existence of life including microorganisms is limited to the planet Earth, and only a range of about 10 km centered on its surface. The question of whether there is life outside Earth has been repeated since ancient times, and no one has the answer yet. But from a cosmic scale, life may be extremely rare.
Let’s get back to the topic. Individual microorganisms cannot be seen with the naked eye. However, if a large number of microorganisms gather, they can be seen with the naked eye. For example, “natto”. If you look closely at natto, there is a wrinkled and slimy substance attached to the surface of the steamed soybeans, which is a state where a large number of bacteria called natto bacteria (Bacillus subtilis var. natto) have proliferated. If you leave mandarins, bread, rice cakes, etc. unattended, mold will eventually grow. Blue cheese has suspicious green substances inside. People who make bread sometimes use dry yeast. All of these are large collections of microorganisms that have become visible.
Even microorganisms that are thought to be too small to see are often seen in our lives if you look around a little. (Figure 1-2)
Figure 1-2 Microorganisms Visible to the Naked Eye
Author
Senior Consultant, GMP Platform, CM Plus Corporation
After working in sterilization management, microbiology, and quality assurance at Johnson & Johnson, Creative Medic, and Boston Scientific, he joined CM Plus, Inc. in 2013.
While working for the medical device manufacturer above, he participated in the Health and Welfare Science Research Group and various sterilization-related committees as a specialist in ethylene oxide sterilization.
About GMP Platform (https://www.gmp-platform.com/)
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