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Coexistence of Humans and Microorganisms: Why Our Microbes Could be Key to Our Health

We live with microbes, even though we cannot see them with our naked eyes. Microbes are the smallest living organisms known. They are everywhere. Some microorganisms live inside our body as well. Bacteria represent the majority of the microorganisms living in the body.

History of life on Earth is largely microbial

Earth’s first life appeared early in the planet’s history, nearly 4 billion years ago. For vast stretches of time, bacteria and other single-celled organisms were the only life on Earth. The rise of photosynthetic bacteria called 'cyanobacteria' was a crucial step in the evolution of life. These bacteria ingest carbon dioxide and release oxygen. Scientists believe that microbes (microalgae) contribute anywhere between 50 to 85 percent of the oxygen in Earth’s atmosphere and very little net O2 is actually produced by plants. Most of the life on the planet is microbial. Life on this planet can run without human beings, but not without microbes.

“Life would not long remain possible in the absence of microbes”— Louis Pasteur

We’re not completely human, when it comes to the genetic material inside our cells. From literature it appears we have roughly around 145 genes that have transferred from bacteria, other single-celled organisms and viruses, and made our body their home. The phenomenon behind this is called Horizontal Gene Transfer, which refers to genes actually moving sideways across species which has contributed to the evolution.

The human body is inhabited by millions of microorganisms, which, all together, are called the human microbiota. They are found on the skin, in the nose, mouth, and especially in the gut and live with us throughout our lives. The human microbiota is involved in healthy growth, protecting the body from invaders and helping digestion, and also benefit and support immunity. So, they are absolutely essential for our survival. Some changes in the microbiota may occur during our growth, depending on the food we eat, the environment in which we live, the people and animals that interact with us, or medicines such as antibiotics that we take.

When we mention bacteria, we might immediately think of illness. However, in healthy individuals, pathogens cause no disease; they simply coexist with us. If we are not able to adapt to the presence of microbes in our system then we see the harm. Do we know that we have more bacteria in our body than the number of human cells? The human body contains trillions of microorganisms — outnumbering human cells by a factor 10 to 1.

The intestines contain the largest portion of the human microbiota called gut microbiota. More than 1,000 different types of bacteria exist in the human gut! Humans have evolved with an intimate symbiotic relationship with gut microbiota. It is known that a healthy microbiota contributes to our health. To be healthy we need to take care of beneficial intestinal bacteria by eating healthy food.

Taking care of the gut microbiota

There are two ways a child can acquire this gut bacteria. One way is to acquire microbes from the mother and another way is from the environment, which is strongly influenced by our lifestyle, environmental exposures to toxins (like alcohol and smoking), medications (like the over-use of antibiotics), stress, lack of exercise, and our diet. A proper diet can cultivate a healthy gut flora. We often eat food with added sugar like cakes, biscuits, brownies, sweet jellies, and white bread, and we also eat a lot of processed and junk food in excess, which are not good for our health. So, we impair the survival and functions of gut bacteria by these unhealthy habits. It’s good to avoid ultra-processed food, alcohol, sugary drinks, and artificial sweeteners or other additives to keep our gut microbiota healthy.

The best way to increase microbiome diversity is by eating a wide range of plant-based foods, which are high in fibre (onions, garlic, beans, chickpeas, cereals, whole wheat bread, apples, berries, citrus, oats, seeds, and roots). These types of foods are called Prebiotics - foods that promote the growth of beneficial gut bacteria naturally. We cannot digest some types of food properly if we do not have our tiny friends in our guts. Therefore, we do not want these good bacteria to die, because they are important to our health. The reduction of these good bacteria will allow the growth of the not-so-good bacteria that can eventually cause health problems. We can also support our microbiome by regularly eating natural probiotic foods.

Probiotics are live microorganisms which have the health benefits for the host, and they are generally consumed as a constituent of fermented foods. They have the ability to decrease the severity of infections in upper respiratory and gastrointestinal tracts. They are mostly the members of the intestinal microbiota.

Many of us know probiotics are the superheroes of our gut health. But do we know that as well as being strong in their ability to protect the gut, they also benefit and support healthy immunity?

Eat to feed our microbiome: Natural probiotic foods

While a person can take probiotic supplements, there are also many probiotic foods available to increase the efficiency of our immune system. Probiotics in fermented foods and supplements may benefit health by breaking down food and boosting the immune system.

Examples of products that contain probiotics include:

  • Traditional buttermilk

  • Yogurt (Fermented milk)

  • Acidophilous milk

  • Soft and aged Cheeses

  • Salt-water brined olives

  • Fresh pickles

  • Fermented soybeans and cabbage

Antiviral effects of probiotics

Recent research has shown that the gut microbiome plays an essential role in the body’s immune response to infection and in maintaining overall health, as well as mounting a response to infectious pathogens. Probiotic bacteria can interact with our gut microbiome to reinforce our immune system, increase immune responses, and promote specific immune signalling with physiological relevance. The potency to shorten the duration of upper respiratory symptoms was reported in Lactobacillus casei, Enterococcus faecium, Lactobacillus plantarum, Lactobacillus salivarius. Lactobacillus gasseri, Bifidobacterium longum and Bifidobacterium bifidum.


In times of pandemics like COVID-19, we have suddenly woken up. General immunity is always an important thing which has to be acquired over a long time through right food and a healthy lifestyle. This can be built only by eating a wide variety of plant-based foods, which are high in fiber and natural probiotic foods. We must learn the right lessons from this outbreak. This is all part of life and this has taught us a few lessons on how to protect ourselves in such situations and practice healthy habits.

In summary, combining a healthy and balanced diet with prebiotics, probiotics, vitamin supplementation and good exercise could help us reinforce our immune system. Cultivating good eating habits at an early age will help children fight any illness anytime.


  1. Da Silva G and Domingues S (2017) We Are Never Alone: Living with the Human Microbiota. Front. Young Minds.

  2. DNA From Viruses, Bacteria Have Weaved Themselves Into Human Genome. By Elizabeth Dohms-Harter G. C. Dismukes et al. The origin of atmospheric oxygen on Earth: The innovation of oxygenic photosynthesis.

  3. Proceedings of the National Academy of Sciences Feb 2001, 98 (5) 2170-2175.

  4. How much do oceans add to world’s oxygen? Posted by EarthSky in EARTH | SCIENCE WIRE | June 8, 2015.

  5. Humans may harbor more than 100 genes from other organisms. By Sarah C. P. Williams Mar. 12, 2015.

  6. NIH Human Microbiome Project defines normal bacterial makeup of the body. Genome sequencing creates first reference data for microbes living with healthy adults. News relesses. National Institute of health.

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