Of Bacteria and Men

My recent Tree of Life post described how all living creatures share a common ancestor. Both Homo Sapiens and the E. Coli bacterium in his bowels belong to the same “extended” family!



In that post I promised to write another blog about bacteria and the human body. Here it is..:-)

We humans are multi-cellular organisms consisting of roughly 10 trillion cells. For those not familiar with the naming of big numbers, one trillion = 1000 billion = 1000000 million. And for comparison, the global human population is at the moment ~ 7.3 billion, so there are ~ 1500 times more cells in your body than there are people living on our planet.

Bacteria are single-cell organisms. How many bacteria do we have in and on our body? A staggering 100 trillion, 10 times as many as we have body cells! They can be found on our skin, on our teeth, basically everywhere, but most of them live in our bowels, the so-called gut flora . The size of these bacteria is roughly 10 times smaller than an average human body cell,  their total mass is estimated to be 1-2 % of our body mass. Mind you, that is still a lot, about 1 kg of your body mass is bacterial!.

Probably you will have been taught that bacteria are bad and dangerous. Wash your hands, keep everything clean, etc. And of course there are bacteria that can harm you, even kill you. But most of the bacteria in/on your body are harmless and many are even needed for your survival. You would die without your gut flora!

Here are a few  things your gut flora will do for you:

  • The bacteria will do part of the digestion and help forming your stool
  • They are important to build your immune system and keep it in good order
  • They will fight harmful (pathogen) bacteria
  • They are needed for the production of Vitamin-K
  • Etc, etc

Together, all of the bacteria in the body would be the size of a large liver, and in many ways, scientists say, this microbiome (as the whole community of microorganisms in our body is often called) behaves as another organ in the human body: the Forgotten Organ…:-)

As the importance of our  microbiome has been recognised more and more in the last decades, some scientists nowadays consider us as superorganisms  or see us as an ecosystem!

Or, as a microbiologist recently formulated it, in a rather extreme way: “we would do well to begin regarding the human body as “an elaborate vessel optimized for the growth and spread of our microbial inhabitants.

A project of the US National Institute of Health, the Human Microbiome Project has been researching the human microbiome. Here is a survey of what they found (click on the picture to see details).The various parts of our body have different bacterial communities.

HMB project

What about a baby, is it born with a gut flora? No, the womb is sterile (although maybe not 100%). But as soon as the baby has left the mother, the bacterial invasion begins and within days the gut flora is there. Essential to build the immune system of the baby!

Interesting detail: the composition of the gut flora is different for Vaginal delivery and Caesarean section delivery. Now it is well known that babies delivered by Caearean section run a higher risk of asthma, allergies and several other health risks, because of the different gut flora. Here is an interesting solution

gut flora

Can you believe it…:-)? It is true.

What about this. The Clostridium difficile bacteria is a common bacteria in soil, but can also live in your bowels. Pathogenic strains of this bacteria can cause diarrhea and inflammation of the colon, especially when the normal gut flora has been damaged by antibiotic treatment. The bacteria itself is resistant against most antibiotics, so it takes over the gut flora. Here is a picture of the bacteria.


Infection with C. Difficile can be life-threatening, it kills approximately 14000 people yearly in the USA.

A promising solution?  Fecal transplantation therapy. Or, in common English: Stool transplant! Take some of the feces of a healthy donor and put it in the colon of the patient. It often works!!

The bacteria in the stool are able to restore the balance in the compromised gut flora of the patient.

Can you believe it…:-)? It is true. Here are some success stories: The Power of Poop