Almost every surface is our body is covered in microorganisms. But by far the largest collection of bacteria are in our gastrointestinal tract - our gut. Collectively, these trillions of microbes are called the gut microbiota, and with all the products they release and the complex ecosystem in which they exist, we term it the microbiome.
It is not always the case that we associate positive effects with bacteria. We usually think of infection, illness and disease. But it turns out that many of our gut microbes are in fact good, and without them, our bodies would not be able to do the many functions it does today.
Up until recently, very little was known about the microbiome, however with advances in very sophisticated sequencing techniques, we are now able to characterise the many species of bacteria, viruses and fungi in our gut, start to understand why they are there, and exactly what they are doing.
Believe it or not, our microbiota is very sophisticated, having evolved with our ever changing lifestyle. They encode for over 6 million genes... a mere 300 x that of the entire human body. There are also many many more of them, than cells in our body, meaning that the microbiota has a much more complex genetic complement than we ourselves have. It therefore comes as no surprise that these microbes can do many things that the cells and tissues in our bodies cannot.
For example, they digest food and produce vitamins, without which we would not survive. Most importantly however, these microbes are critical in shaping our immune system, helping us learn when to be tolerant of particular bugs, and when to fight nasty infections. This has seen the microbiota now linked to diseases such as asthma, allergies, diabetes, inflammatory bowel disease, arthritis and even cancer.
But what drives our microbiota composition? This has been an area of intense research efforts to better understand the aetiology of diseases and new ways to prevent or treat them. And it turns out that much of the microbiota is in deed hereditable, with much of it coming from your mother during childbirth. Microbes begin colonising our gut and skin the moment we are born, and interestingly, it is different based on whether you are born vaginally, or by caesarian.
Vaginally-delivered babies acquire many microbes through direct contact with their mother, this is known as vaginal-transfer. These babies tend to have more microbes that are deemed "healthy". In contrast, caesarian born babies tend to have higher amounts of microbes that reside on the skin and on surfaces, such as those in the hospital. Although the permanency of these microbes are unclear, some research now suggests that this can have profound effects on the early development of the microbiota and may therefore regulate our risk of developing certain diseases during life.
What we also know about the microbiota is that it is very malleable, and it changes in response to a wide variety of environmental triggers. Antibiotic treatment and diet are the frontrunners for changing the composition of the microbiota, and are therefore attracting the most attention for their role in the development, and treatment of diseases associated with the microbiome.
We are now starting to understand the complexities of our microbiome, its role in disease and potential as a therapeutic target. But it is important to remember that this multi-functional, multi-cellular ecosystem has a bi-directional relationship with the human body. So research in this area must be treated with caution to ensure that sensationalised causative claims are not made in place of associations. But nonetheless, we are starting to realise that the microbiome is certainly more powerful than we ever imagined, and it is reasonable to view it as any other organ of our body, because at the end of the day, we are more bug than human.