Microbiome and microbiota

Although they are often used interchangeably, microbiome and microbiota are different terms. The microbiota identifies the population of commensal, symbiotic or pathogenic microorganisms that colonise specific areas in our bodies, for example, the skin, nose, intestinal tract, and vagina.

The human microbiota has an important role in providing a protective physical barrier, releasing antimicrobial substances against pathogens, stimulating the immune system, breaking down potential toxins, and synthesising certain micronutrients.

It is essential that this dynamic system adapts to external and internal stimuli to maintain a state of equilibrium to ensure the wellbeing of the organism. Imbalances in the microbiota can lead to the development and progression of infectious diseases, liver diseases, autoimmune diseases, gastrointestinal cancers, metabolic diseases, respiratory diseases, and mental or psychological conditions.

The microbiome refers to all the genetic heritage that characterises the microbiota and the genes that are expressed. A person’s microbiome is formed in childhood and is influenced by diet, medications, and environmental exposures. Differences in the microbiome may also determine a person’s susceptibility to conditions such as metabolic disorders, allergies, cancers, cardiovascular and neurological disorders, and their responses to medications.

The intestinal microbiota

Your gut contains up to 10-1000 billion bacteria per millilitre of faeces material. It is estimated that over 30 tonnes of food and over 50,000 litres of liquids pass through the intestine during a lifetime. Food digestion takes place thanks to anatomical structures such as the villi and microvilli, and the microbiota that is constantly “stirred” by peristaltic movement. Certain types of anaerobic bacteria are found in the gut, which compete with harmful microorganisms for nutrients and attachment sites on the gut lining.

The intestinal lining constitutes around 70 per cent of the body’s immune system. Within the walls of the intestine, special regions called gut-associated lymphoid tissue (GALT) contain immune cells that recognise, identify and neutralise harmful substances. The interactions between gut bacteria and the immune cells are known to have an essential role in the maturation of the immune system.

Similarly, a two-way biochemical signalling pathway between the intestinal tract and the central nervous system, called the gut-brain axis, links the microbiota to the brain, affecting the stress response, anxiety and memory function. Hence, the gut is often referred to as the second brain, playing a significant role in brain function and mental health.

The vaginal microbiota

The composition of the vaginal microbiota varies depending on age, hormone levels, sexual activity, drug use, and intimate hygiene. For a woman’s general wellbeing, it is fundamentally important that this body area is colonised by microorganisms that hinder the colonisation and proliferation of pathogens, reducing the risk of infections and inflammatory states. A healthy vaginal microbiome is dominated by Lactobacillus, which produces a variety of antimicrobial compounds.

Skin microorganisms

Our skin covers nearly two square metres of our body and is our first line of defence against pathogens and harmful substances; crucial to its function is the colonising microbiota. The skin microbiota is formed at the time of birth and changes during adolescence but remains almost unchanged during adult life.

The microorganisms that colonise our skin vary according to the structural and functional state of the skin at that given moment. In addition, the different areas of the body have different degrees of hydration and percentage of sebum. Consequently, the microbial population on the skin surface is not homogeneous. Studying the composition of the microbiota at different sites is valuable for demonstrating the cause of common skin disorders, such as eczema on the inside of the elbow and psoriasis on the outside of the elbow. Many skin disorders are associated with changes in the microbiota (dysbiosis), often driven by common commensal bacteria—for example, acne, a common skin condition during the teenage years.

The oral cavity

The oral cavity is considered one of the largest microbiological reservoirs of the human body, being colonised by a diverse microbial community of more than 700 different species of bacteria, fungi, and even protozoa. The oral microbiota plays a vital role in maintaining oral homeostasis and preventing the development of oral and dental diseases. Its immediate proximity to the external environment leaves it more vulnerable to dysbiosis processes, accentuated by factors such as smoking and alcohol. The increase in the number of harmful bacteria, at the expense of beneficial ones, changes the oral microenvironment with an increase in inflammatory processes.

Another feature that makes the oral microbiota unique is the ability of these cells and bacteria to aggregate, adhering to the surface and enamel of the teeth by means of proteins present in saliva. Owing to this aggregation, the biofilm that constitutes dental plaque is created, which calcifies, causing the formation of tartar.

In a healthy patient who observes good oral hygiene standards, the numerous bacterial species that populate the oral flora live in balance and strengthen the immune system of our body. Still, a slight variation is enough to determine the origin of various pathologies of the oral cavity, such as periodontal disease, canker sores, caries, and halitosis.