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Tiny but mighty: The powerful role of gut bacteria in human health and disease

C. difficile bacteria
We need to care more about what we eat and how it influences our wellbeing because it’s not just us we are feeding. Our diet also affects the thousands of microscopic species living in our guts, which in turn influence everything from our mood to our sleep, as well as our digestion. Dr Blessing Anonye from the School of Life Sciences at Warwick, explains the role our gut bacteria play in relation to our health and considers the benefits of having specific bugs in our systems.

The human gut is home to diverse and numerous microbes, known as our intestinal microbiota. They play essential roles in our development, general wellbeing and sustenance. These microbes include viruses, fungi, and primitive life forms called eukaryotes and archaea, but it is bacteria that make up the lion’s share of the population in there. Estimates suggest about 1000 different species of bacteria inhabit the average human gut and these are mostly anaerobic species – those that thrive in environments without oxygen.

Most people know that our gut bacteria contribute to the healthy status of their human host by helping to digest the food we eat and breaking down dietary fibre. But there is a whole range of additional functions that we are beginning to understand. They produce vitamins and nutrients that we can’t synthesise and convert foreign substances to less harmful products. Our gut microbiota also contribute to our immune system development and resistance to disease by acting as a barrier against harmful pathogens.

This little rainforest we have inside us is affected by factors such as diet, hygiene, lifestyle, host genetics and immune status. Variations in these different factors influence the type of gut bacteria present in our gut and the role they play.

Vital to human health

Bacteria in our guts play several roles which make them vital to our health.

They make short chain fatty acids: When we eat, various enzymes in our saliva and also in our stomach start the digestion process. However, not all food is digested by this stage. Undigested food passes through the small intestine and our gut bacteria use it in the large intestine to produce short chain fatty acids. These short chain fatty acids are an energy source for the specialist epithelial cells lining the gut. This is a massive process and one that constitutes about 10% of human calorific requirements.

They aid colonisation resistance: Gut bacteria protect the intestinal lining from invading pathogens. A healthy gut microbiome means good bacteria outcompete the invading pathogens so they can’t survive in numbers which harm us. They also produce antimicrobial by products which inhibit the pathogen from growing and thriving.

They generate vitamins: Gut bacteria can produce vitamins such as K and B groups including folates, biotin, thiamine, pyridoxine, cobalamin and riboflavin. This is particularly important for the host since humans cannot synthesize most of these vitamins.

They make harmful substances into less harmful ones: Intestinal bacteria help in the conversion of harmful substances, known as xenobiotics, into less harmful substances through the use of enzymes. For example, bacteria groups such as Bacteroides and Lactobacillus produce bile salt hydrolases which help to reduce the toxicity of the primary bile acids in the liver and converting them to much less harmful secondary bile acids.

They are involved in a healthy immune system: Bacteria in the gut aids in the development of your innate and adaptive immune responses. Through promoting immunological tolerance by suppressing inflammatory response and differentiating between pathogenic invasion and commensal interaction to elicit an appropriate response.

Specific gut bacteria beneficial to health

There are some really important gut bacteria to have in your microbiome, though this list is not exhaustive.

Bifidobacterium are the first colonizers of the infant microbiome, especially in babies fed with breast milk, and have positive health benefits on the host such as colonization resistance, by competitive exclusion through binding on common sites on epithelial cells.

Faecalibacterium prausnitzii, a dominant bacterium found in a healthy gut has been indicated as a marker in certain diseases. Studies show that individuals with Crohn’s disease, a type of inflammatory bowel disease, have a reduced population of this particular type and that, F. prausnitzii possess anti-inflammatory effects.

Bacteroides dorei, a major gut bacterium present in healthy individuals was recently shown to inhibit the particularly dangerous C. difficile in a complex human gut cellular model of infection.

Akkermansia muciniphila, a mucin degrading bacterium is present in 3-5% in healthy adults. Results from different studies on diet-induced obesity have shown an increase in Akkermansia is associated with decreased weight gain and fat deposition and improved glucose tolerance.

Gut bacteria in disease

When colonization resistance is disrupted, either through taking antibiotics which leads to reduced diversity and abundance of “good bugs”, or infection, diseases such as Clostridium difficile infection, inflammatory bowel diseases and other intestinal diseases becomes very likely. Loss of colonization resistance also lead to expansion of pathogenic organisms (“bad bugs”) that affect the human host.

C. difficile, an anaerobic bacterium, is the main cause of antibiotic-associated diarrhoea in hospitalised patients and can lead to death if left untreated. Major risk factors include prolonged antibiotic use and old age. It produces toxins and spores and these are known to be the main means by which it causes disease. These spores can persist on environmental surfaces and in the gut of infected individuals. They germinate to the infectious form when antibiotic therapy is stopped leading to recurrent infection. Individuals with recurrent disease can now receive faecal microbiota transplantation to cure the disease.

Other diseases linked to disturbances or influence of the gut microbiota include inflammatory bowel disease, type 2 diabetes, obesity and cancer. So, maintaining a healthy balance of “good bugs” and keeping the “bad bugs” under check is critical for your general well-being.

Fruit and vegetable selection

Please feed the bugs

Ultimately we know what to do. We should cut the bad foods and increase our intake of fresh fruits and vegetables. We should eat plenty of fibre and also think about introducing fermented foods – like live yogurt, or Kimchi, a traditional fermented vegetable dish of Korean cuisine. If you think about keeping your microbiome happy, ultimately it will keep you healthy.





11 February 2020


Dr Blessing AnonyeDr Blessing Anonye is a microbiologist interested in understanding the human intestinal microbiota in health and in disease. She worked in Warwick Medical School where she performed research on understanding host-pathogen interaction in Clostridium difficile using human gut cellular models of infection. Her current research is in the School of Life Sciences focussing on developing alternative plant based remedies for the treatment of bacterial infections.

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