The role of the microbiome in our body

Around 90-95% of the human microbiome can be found in the gastrointestinal tract, especially the colon, where it has a role in multiple bodily functions. — Positive Parenting

There are microorganisms that live on and within each individual human being.

These microorganisms are found in various parts of the body, including the gastrointestinal tract, vagina, skin, respiratory tract, urinary tract and the breasts.

The term “microbiome” has been defined as all the microorganisms found in a defined environment, including the human body or part of the human body.

These organisms comprise bacteria, viruses, archaea (which are similar to bacteria in size, but very different in molecular organisation) and eukaryotes (which are organisms in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus – yes, humans are eukaryotes).

The number of these microorganisms have been estimated to exceed the number of human cells considerably.

It has been estimated that 90-95% of the human microbiome is found in the gastrointestinal tract, especially the colon.

In contrast, the stomach and small intestine are more sparsely colonised.

Previously, microorganisms were found to cause various diseases, e.g. Mycobacterium tuberculosis causing tuberculosis, the herpes simplex virus causing cold sores, etc.

However. with diagnostic advances and analytical techniques, it has been increasingly recognised that, in most instances, the relationship between humans and their microbiome have been mutually beneficial.

Apart from the functions played by the microbiome in the gut, it is believed that the human microbiome has several other functions, which include bolstering the immune system; influencing the functioning of the brain, liver, kidneys, skin and vagina; affecting blood lipids; and producing and modulating hormones.

While there is much that is known about the human microbiome in health and disease, there is also still much that is unknown.

This is illustrated in three common microbiomes below.

> Gut microbiome

While the ideal gut microbiome is not known, scientists agree that these microorganisms – and their activities – play an important role in human health.

It is known that gut microorganisms improve gut motility and function; harvest energy from foods; produce vitamins, hormones and important metabolites that are important for health; protect against harmful organisms (pathogens); and reinforce the gut barrier.

The gut barrier is a multi-layered functional unit that comprises two main components: a physical barrier surface, which prevents bacterial adhesion and regulates paracellular diffusion to the host tissues; and a deep functional barrier that discriminates between pathogens and commensal microorganisms (which are harmless).

The physical barrier is composed of gut microorganisms that compete with pathogens for space and energy resources, ensures mucosal integrity, and modulates the immunological activity of the deep barrier.

The composition of the gut microbiome stabilises about the age of three years, prior to which the microorganisms are likely to have been acquired from close contacts and family members.

It has been predicted that the gut microbiome is then maintained throughout the person’s life.

If the gut microbiome is disturbed, opportunistic pathogens and the negative activities of gut microorganisms can increase.

The latter is associated with conditions like antibiotic-associated diarrhoea, inflammatory bowel disease, irritable bowel syndrome, colon cancer, diabetes, metabolic syndrome, obesity, allergies, depression and anxiety.

However, it is unclear if an abnormal microbiome causes, or is a consequence of, these conditions.

Many pharmaceuticals used in the treatment of gastrointestinal disorders act through the restoration of normal intestinal permeability.

> Vaginal microbiome

The vaginal microbiome lives in a dynamic environment that is affected by age, ethnicity, menstrual cycle, sexual activity, pregnancy and contraceptive use.

The normal vaginal flora is dominated by lactobacilli, which vary with ethnicity.

Lactobacilli acidify the vaginal environment, thereby protecting it from potentially pathogenic microorganisms that may lead to urinary tract infections and sexually-transmitted diseases.

Changes in the vaginal microbiome, including reduced lactobacilli, and increased facultative and anaerobic microorganisms, lead to bacterial vaginosis.

Bacterial vaginosis predisposes to several conditions like low birth weight in babies born to the woman, and an increased risk of contracting bacterial infections.

The vaginal microbiome is of particular significance in the post-menopausal period as it may have a significant impact on vulvovaginal atrophy, vaginal dryness, sexual health and overall quality of life.

> Skin microbiome

The skin is the part of the human body that interfaces with the environment.

It is a physical barrier that prevents the invasion of foreign pathogens, while providing a home to numerous bacteria, viruses and other microorganisms.

The skin microbiome of a healthy adult remains stable over time, despite environmental changes.

These microorganisms have adapted to an environment that have scant nutrients available.

The skin microbiome plays an important role in the cutaneous immune system, with many skin microorganisms either producing chemicals that inhibit colonisation by foreign microorganisms, or altering their behaviour.

The initial colonisation of the skin by microorganisms is dependent on how the baby is delivered.

Newborns delivered vaginally acquire bacteria that have colonised their mother’s vagina, whereas newborns delivered by Caesarean section acquire microorganisms that are associated with the skin.

The skin microbiome is restructured during puberty when sex hormones stimulate the sebaceous glands to produce more sebum, which favour lipophilic (fat-loving) microorganisms.

Some skin conditions are associated with an altered microbiome.

Reverting the microbiome to its original state may help prevent and/or treat the condition.

For example, microorganisms are associated with acne, atopic dermatitis (also known as eczema) and chronic wound infections.

However, many questions remain regarding the function of the skin microbiome, e.g. what role do microorganisms have in maintaining health or promoting disease?

Maintaining your microbiome

There are several actions individuals can take to ensure their personal microbiome is not disrupted. These include:

• Taking antibiotics and other medicines only when there is a need.
• Maintaining a healthy weight.
• Exercising.
• Consuming a healthy diet, especially vegetables and foods with fibre.
• Remembering that different approaches may be required at different stages in life.
• Keeping yourself informed.
• Seeking advice and information from your regular doctor, other healthcare professionals and authoritative websites (usually that of governmental agencies and professional organisations).

Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations and the Malaysian Medical Association. For more information, email [e-mail]. The views expressed do not represent that of organisations that the writer is associated with. The information provided is for educational and communication purposes only, and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.