Opinion Living with the microbiome

Our bodily functions are controlled not only by the 23,000 genes carried by our cells but also by the 3 million genes carried by the microbiome. It appears that the composition of the microbiome is distinctive to each person and varies even between identical twins. Since the expression of both human and bacterial genes can be altered by a variety of human behaviour,we need to understand how the composition and function of this vast gene pool alters over a human’s lifetime.

Twentieth century medicine taught us to fear and fight bacteria. The germ theory of disease dominated medical thinking and antibiotics became our principal weapon of warfare against real and perceived bacterial invasions. Even the lay person was conditioned to think of bacteria as threats whose presence in the human body spelt danger. One only has to see the frequent toothpaste ads on television,exhorting us to exterminate all bacteria from the mouth,to realise how the fear of bacteria is relentlessly instilled and reinforced in the human mind.

Recent scientific know-how says that while there are indeed bacteria that can produce disease under certain conditions,there are also classes of bacteria that are part of our very existence. They help us to resist and fight dangerous infections caused by other bacteria,make some essential vitamins,boost our immunity,protect us from allergies and assist us in digesting food that cannot be broken down by the enzymes produced by our body.

Disruptions of the microbiome can lead to harmful health effects ranging from allergies and asthma to chronic diseases such as diabetes,obesity,high blood pressure,heart disease,multiple sclerosis,autism, irritable bowel syndrome and bowel cancer. New therapies are attempting to maintain or modify the microbiome,in order to prevent or treat disease. The Economist reports on how stool transplants (via enema,mercifully) are now being used to introduce “good bacteria” into the bowels of patients to treat serious hospital infections. Hopefully,we will quickly discover less challenging ways of boosting our bacterial batteries.

How do we acquire these allies who become part of our body till death (ours or theirs) do us part? During natural birth,a baby is gifted with good bacteria while passing through the mother’s birth canal. Later,during infancy,the mother’s embrace transfers some more. As the child grows,bacteria also come in from other humans and through food,drink and the external environment.

It has been observed that children born through a caesarean section are more prone to allergies than children who had a natural birth. This is because the protection offered by the bacteria picked up from the mother’s genital passage during natural transit is not available to the baby who is extracted directly from the uterus.

Indiscriminate use of antibiotics damages the microbiome by killing many of the helpful bacteria. Diet,tobacco,alcohol and environmental toxins also affect these bacterial colonies. We clearly need to pay more attention to our living habits,lest we upset the harmony of our co-existence. The problem is we still do not know how to manage this relationship.

Perhaps ayurveda and other traditional systems can provide guidance in this area. They place a great emphasis on how certain foods agree or disagree with a person,although they do not know about the specific effect of each food on a person’s microbiome. Even as modern science spectacularly advances our understanding of human biology,modern medicine can benefit from working with other systems of medicine whose accumulated observational wisdom seems to provide intuitive insights into maintaining health rather than just treating disease.

In the 21st century,medicine has to evolve through greater recognition of and respect for the interdependence of life forms and take into account the effects of both the microenvironment and the macroenvironment on human health and disease. As it does so,it is my (“our”) gut feeling that we will hear a good deal more about the microbiome.

The writer is president of the Public Health Foundation of India

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