How many microbes live on us?

All this COVID “remove the germs” hype got me skeptical. As a microbiologist, I’m against antibacterial soaps and never let my kids use them. These days however I have no choice. We are scrubbing and sanitize our hands till they feel like glass.

I had been researching the auto-generation of bacteria on our hands after sanitizing and it made me wonder; apart from the hands how many bacteria actually live on us.

If you have ever looked up the answer online, you would invariably be informed that the number is 10 bacteria cells vrs 1 of ours. This number was calculated by Dr. Luckey during a study in 1972. That number doesn’t seem right., and it isn’t. His mistake was overestimating gut bacteria quantities by wrongly assuming the same amount resides throughout the entire gut canal.  Whereas there are concentrations in some places as compared to others.

Ron Milo and his team at the Weizmann Institute of Science in Rehovot took it upon themselves to recalculate these estimates. They based their estimates on an imaginary 20 to 30 yrs. old they called “Reference man, whose weight was 70 kg and height was 1.7 meters.

Such a person’s body would comprise 30 trillion human cells and house 39 trillion bacteria. Obviously, these numbers would vary from person to person and the authors themselves admit uncertainty, but we can assume that the ratio is more 1:1.3 rather than 1:10.

Where are there the most microbes on us?

So, what and where are all these cells? Most human cells comprise muscle, tissue, fat, and blood, and most of the bacterial cells reside in our colon.

No matter how much you keep clean, our bodies are covered with foreign life, but inside and out. These include bacteria, viruses, and archaea. The greatest concentration lives in the dark humid and nutritionally enriched bowels; and for a good reason.

These tiny living creatures are essential for our health, but that doesn’t mean you shouldn’t brush your teeth or wash up!

It is now being understood that the condition and concentration of our microbiome are linked with many diseases, including cancer. It’s true, you are what you eat, or rather what you feed your bacteria.

How much weight of microbes are on us?

Unfortunately, no. You can’t blame your weight on your bacteria. Dr. Milo estimates that there is about 200 gm of microbes on us by weight.

To make that simpler to understand, one tablespoon can contain 15 gm of water. So around 13 tablespoons of water is an equivalent amount of microbes in a person.

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I have to say, it’s very impressive that, comparable by weight, such a small amount of organisms can have such an impactful role on their larger human hosts.  From managing our digestion to causing disease these tiny organisms are living complete and purposeful lives on and around us.

The human microbiome project has elucidated thousands of different bacterial types, each choosing specific body areas where they form communities and have different interactive roles.

We as humans always assume, we know what’s best, but oftentimes we are actually naive in our understanding of nature’s processes going on around us. In reality, there is little we are in control of, the human microbiome project is proof of that.