A-Z Glossary of Probiotic and Gut Terms
Have you come across a term or phrase that you don’t understand? Welcome to our Glossary – designed to help explain the long list of jargon associated with the gut in general and probiotics in particular.
Please do contact us if we have missed anything – we are constantly updating our Glossary to keep up with changes in our industry and as we add more content to our website.
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Acidophilus is one of the more well-known species of bacteria and belongs to the Lactobacillus group, which is one of the primary species of probiotic bacteria found in the human gut microbiome. Lactobacillus is mostly situated in the small intestine.
Acne is a skin condition that affects many people and symptoms include spots and oily skin. Acne and spots are caused by inflammation of the sebaceous glands and has been linked to gut dysbiosis.
Aerobic bacteria need oxygen to survive, reproduce and grow. They are more aerobic bacteria than anaerobic bacteria in our bodies.
Aetiology is derived from Greek and means 'giving a reason for'. It is used in healthcare to refer to the factors or causes that might have led to the current disease.
Anaerobic means living or producing energy in the absence of oxygen. Anaerobic bacteria do not need oxygen to live and can produce energy in an environment that does not contain oxygen.
Antibiotic-associated diarrhoea, or ADD, refers to diarrhoea that occurs as a result of a course of antibiotics. It occurs in around 5-30% of those taking antibiotics and involves loose, watery stools and fever. It results from the disruption of the normal gut microflora caused by the antibiotics, which destroy the existing gut bacteria and thus allow the overgrowth of bacteria that cause diarrhoea.
Antibiotics are medicines sided to treat or prevent some types of bacterial infections in the body. They work by killing the bacteria or preventing them from reproducing or spreading. They are anti-bacterial and do not work for viral infections. Examples of antibiotics include penicillins and tetracyclines. As they work by killing bacteria, antibiotics destroy both the good and bad bacteria in the gut and affect the healthy balance of our microbiome.
Antibodies are proteins produced by the immune system in response to pathogens (foreign substances or antigens) to stop them entering the body and causing harm. Also known as immunoglobulins, antibodies recognise the pathogens and work to neutralise them and help to remove them from the body.
An antigen is a foreign compound that causes the immune system to respond and produce antibodies. They include substances produced by viruses, bacteria, pollen grains and large carbohydrates.
Antioxidants are compounds that work in our bodies to decrease or slow oxidation, protecting our cells from free radicals (oxidants) which can cause degeneration to the cells. Oxidation is a chemical reaction that occurs throughout the body in normal everyday metabolism and can produce free radicals, which may damage cells. Examples of antioxidants include flavanoids and polyphenols.
Asthma is a respiratory condition that affects the tubes that carry air in and out of the lungs. It often causes symptoms such as coughing, wheezing and difficulty breathing. It is often related to other allergies, such as eczema and hay fever.
Atopy is a predisposition to developing allergies or allergic reactions. It is often hereditary and typically involves eczema (atopic dermatitis), allergic rhinitis (hay fever) or allergic asthma - some atopic people have all three. People with atopy also have a tendency to other allergies, including food allergies.
Autism spectrum disorder (ASD) is a development disorder that involves difficulties with social interaction and communication and restricted and/or repetitive behaviour. Many people with autistic spectrum disorder are reported to have gastro-intestinal problems. Autism, as it is more commonly known, occurs along a spectrum, meaning that the condition will affect people in different ways and with varying degrees of difficulty. Asperger syndrome is a form of autism considered to be at the mild end of the spectrum.
Autoimmune (AI) disease occurs when the immune system mistakenly responds to a normal body part and attacks the body's own tissues. There are more than 80 AI diseases, including, type I diabetes, rheumatoid arthritis and inflammatory bowel disease and there is thought to be a link between AI disease and the gut.
Bacillus species of bacteria are widely distributed in the environment mainly in soil. They are spore-forming organisms, which are often considered to be contaminants. As this species of bacteria can become dormant in harsh environments, it is particularly hardy and able to survive extreme conditions. Some species, such as Bacillus coagulans are considered to be beneficial probiotic bacteria, but they do not have as much safety evidence as the Lactobacillus and Bifidobacteria species.
Bacteria are unicellular (single cell) microorganisms belonging to the "prokaryote" kingdom of organisms. They are characterised by their lack of specialised internal organs or any organised nucleus. Bacteria are not visible to the human eye and are able to reproduce asexually, growing and dividing their cells at incredible speed. Bacteria can be pathogenic (bad) or beneficial for human health. Bacteria that are beneficial to human health are referred to as probiotics or friendly bacteria. Commensal bacteria are native to their host, ie. they live in a relationship in which one organism derives food or other benefits from another organism without hurting or helping it.
These are a genus of gram-negative bacteria which makes up a significant proportion of the gastrointestinal bacteria in mammals. They are involved in many important metabolic activities in the human digestive system including helping to break down complex carbohydrates into more simple ones. Bacteroides are beneficial to the host as long as they reside in the gut, although they may cause infections and abscesses if they move to other parts of the body..
The Bacteroidetes group (or phylum) of bacteria is composed of three large classes of gram-negative, non-spore forming, anaerobic, and rod-shaped bacteria. They are widely distributed in the environment, including in soil, sediments and sea water as well as being found in the guts and on the skin of animals.
The Bacteroidia class is the most well studied and is present in the digestive tract of most mammals, and includes the Bacteroides genus.
Probiotics such as Lactobacillus acidophilus adhere to the epithelial cells that cover the gut wall lining. The good, probiotic bacteria decrease the amount of available space for pathogens (harmful bacteria) to bind, effectively creating a protective barrier against pathogens; resulting in what is known in microbiology as the 'Barrier Effect'. The Barrier Effects is one key way in which probiotics are thought to be good for immunity.
A genus of gram-positive, non-motile, often branched anaerobic bacteria. They are ubiquitous inhabitants of the gastrointestinal tract, vagina and mouth of mammals, including humans. Bifidobacteria are one of the major genera of bacteria that make up the gastrointestinal tract microbiota in mammals.
Bifidobacterium (singular) or Bifidobacteria (plural) is a genus, or family, of bacteria generally found in the large intestine. Types, or species, of Bifidobacteria include bifidum, infantis and breve. Over the age of 60, levels of Bifidobacteria in particular are thought to largely deplete in the gut.
Bifidum is a probiotic species belonging to the Bifidobacterium family. Bifidobacterium bifidum will naturally reside in the large intestine. Different strains of Bifidobacterium bifidum will have different properties, for example Bifidobacterium bifidum Rosell-71 is β-galactosidase positive (β-galactosidase is an enzyme required for the digestion of lactose.) It is particularly resistant to gastric acidity at a pH over 4, which is why it is recommended to take it at mealtimes.
Bifidobacterium breve is a probiotic species believed to have particular benefits in the inhibition of pathogens. Different strains of breve are sourced from different mediums and can have different qualities. The strain Bifidobacterium breve Rosell-70 for example is a strict anaerobic, gram-positive rod of human origin. This specific strain is both β-galactosidase positive and a-glucosidase positive.
'infantis' is a probiotic species belonging to a family of bacteria called Bifidobacteria. Bifidobacterium infantis can be found in the microbiota of infants, children and adults, although it is found in higher concentration in infants and is thought to be beneficial for childrens' wellbeing and immunity. Interestingly, breast-fed infants have shown higher volumes of Bifidobacterium infantis in the faeces than children who were bottled-fed.
As for all probiotics, it is important to look at the specific strain within the infantis species in order to determine its qualities. Bifidobacterium infantis Rosell-33 for example is an anerobic, gram-positive rod isolated in pairs or short chains.
Bifidobacterium lactis is a species from the Bifidobacterium genus (family) of probiotics. Bifidobacterium lactis is one of many types of probiotic bacteria in the large intestine that makes up the human microbiota. Different strains of probiotics have been tested for different properties, so as with all all probiotics, it is worth being aware of the specific strain.
For example, Bifidobacterium lactis BB-12® has been scientifically researched to help maintain regular bowel movements, and is probably the most researched strain of the B. lactis probiotic in the world.
Bifidogenic means to stimulate the growth of Bifidobacteria in the intestines. Prebiotics must be bifidogenic to fulfil their role of feeding the friendly bacteria in the gut and helping them to multiply and colonise.
A biofilm is a collection of microorganisms that have adhered to each other upon a surface. The formation of biofilms can occur on living and non-living surfaces and is often a reactionary response to the microorganisms environment. Biofilms are thought to be responsible for most microbial infections in the human body.
A blind trial is an experiment in which the participants do not know certain information about the experiment in which they are participating. This may include such information as to whether they are in the experimental group or the control group.
Bloating is a feeling of tightness and fullness in the abdomen, often causing a visible protrusion of the abdominal region or tummy. Bloating affects both men and women, and can be caused by excessive intestinal gas, the menstrual cycle, or overeating. It is also thought to be a symptom of dysbiosis.
Bloating can be a symptom of serious illness such as bowel or ovarian cancer. Anyone with persistent bloating should see their GP. This site does not provide medical diagnosis or treatment.
Blood Lipids is the term used for all the fatty substances found in the blood, including cholesterol and triglycerides. Lipids join with protein in your blood to form lipoproteins which make energy for your body, so they're important to the cells in your body. There are three types of lipoproteins (also known as cholesterol). High-density lipoprotein (HDL), low-density lipoprotein ( LDL) and very low-density lipoprotein (VLDL). HDL is sometimes called the “good cholesterol” because it keeps cholesterol from building up in your arteries. LDL can be thought of as the “bad” cholesterol because high LDL levels can increase your risk of heart attack or stroke. It is the balance between the two which is important when monitoring your cholesterol levels.
Broad Spectrum Antibiotics are antibiotics that work on both gram-positive and gram-negative bacteria. These can therefore be used for a variety of bacterial infections.
A Caesarean section or C-section is the procedure in which the baby is delivered by surgical extraction from the uterus, as opposed to vaginal birth. C-sections are normally performed when complications arise in pregnancy or labour meaning that vaginal birth is no longer the safest option for mother and/or baby.
Interestingly, a direct positive correlation has been shown between babies born by caesarean-section and babies and infants with digestive problems; possibly due to the fact that caesarean babies do not absorb friendly bacteria from the mother's birth canal during the birthing process.
Candida albicans (often simply referred to as Candida) is a yeast-like fungus which feeds on sugar. It can be found in the flora of the mouth, skin, intestinal tract and vagina; many people have small amounts of Candida albicans in the body without experiencing any negative side effects or symptoms. When allowed to overgrow however, Candida albicans can cause inflammation and itching, leading to infections such as thrush. Candida overgrowth cannot be treated by antibiotics as it is fungal, therefore doctors often prescribe anti-fungal medicines, or opt for natural supplements including probiotics.
Capsules consist of an outer casing that is filled with a powder or liquid, whereas tablets are manufactured by compressing and compacting ingredients together. Capsules usually contain less excipients or fillers than tablets, and are easier to swallow because of their shape.
Cardiovascular disease or CVD is a general term that refers to a disease of the heart or blood vessels. It includes coronary artery diseases (CAD), such as angina and myocardial infarction (commonly known as a heart attack).
Cerebrovascular disease refers to a group of conditions that develop due to problems with blood supply to the brain. This happens when there is either limited or no blood flow to affected areas of the brain. Hypertension and atherosclerosis are among the main causes. Cerebrovascular disease may be better known as stroke, transient ischemic attack, subarachnoid haemorrhage, vascular dementia.
Cholesterol is a fatty substance produced by the body, in the liver. It can also be found in some foods. Cholesterol is carried around the body by two lipoproteins, LDL & HDL. LDL (known as the ‘bad’ cholesterol) carries cholesterol from your liver to your cells, and HDL carries cholesterol back to the liver for excretion from the body. Too much LDL in the blood can cause a build up in the arteries and can increase the risk of heart disease and raised blood pressure.
Clinical trials are research studies that involve patients with the aim of exploring various medical treatments for an identified health problem or testing new means for prevention of certain illnesses. These research are carried out under strict conditions to establish the safety of these trials for the general population. Possible side effects and safety cautions are identified in many clinical trials. There are different types of clinical trial, based on the study design. Randomised control trials, cohort studies, and ecological studies are examples of clinical trials.
Members of this ancient genus of bacteria are found throughout the environment in places such as soil, and includes some species which are pathogenic to humans. They are responsible for causing tetanus and some forms of food poisoning. Clostridium difficile is a member of this genus.
Also called C. diff or C. difficile, Clostridium difficile is a bacteria that occurs in small amounts in many people's large intestine. If the number of Clostridium difficile bacteria increases greatly however, it can lead to infection. People suffering from C. difficile infection experience varied symptoms, from mild or severe diarrhoea to severe inflammation of the bowel. In some cases, particularly amongst the elderly, it can cause death. C. difficile infection is often thought to be caused by antibiotics, which can diminish probiotic levels in the gut and allow for overgrowth of C. difficile. The bacteria can be contagious and is often referred to as a superbug.
Coeliac disease is an autoimmune condition caused by an immune reaction to gluten (gluten is a protein found in wheat, barley and rye). According to 'Coeliac UK' the disease affects 1 in 100 people, although only 24% of sufferers have been diagnosed. The ingestion of gluten by a person suffering with coeliac disease, causes damage to the intestinal lining, resulting in an array of symptoms, including: bloating, nausea, diarrhoea, constipation, fatigue, anaemia, and in some cases hair loss. The only treatment for coeliac patients, is to follow a completely gluten-free diet.
A term referring to a human’s ability to process thoughts that should not deplete on a large scale in healthy individuals. It is defined as "the ability of an individual to perform the various mental activities most closely associated with learning and problem-solving.
Infant Colic is a general term for a condition where the baby cries very often, for long periods of time, with no obvious reason as to why. Colic is often associated with digestive problems such as indigestion, food allergies, gas or intestinal cramps.
Colonic inertia is a motility condition that affects the muscles in the colon, meaning that waste is passed abnormally through the gut. Colonic inertia is relatively common and often associated with constipation. The condition can sometimes be caused by the long-term use of stimulant laxatives.
Microorganisms such as bacteria and yeast live all over the body, in the gut, in the vagina, on the skin etc. When microorganisms stick onto the body, start multiplying, and growing in number they are said to have colonised. Not all bacteria are able to colonise in all areas of the body. Some probiotics are good at colonising in the gut whereas others are good at colonising in the vagina. The ability of a probiotic to colonise can be measured in a lab by assessing how well the probiotic strain sticks onto intestinal cells in a glass dish. Or it can be measured by taking a vaginal swab to see how well the probiotics taken orally have colonised in the vagina.
These non- pathogenic types of bacteria naturally coexist with humans in a non- harmful symbiotic relationship, which does not impact negatively on the health of the human host.
This principle refers to the idea that when two different organisms which require the same resources exist in the same environment, eventually one of them will be eliminated or displaced by the more dominant organism.
Constipation is defined as having difficulty in passing stools, or having hard and dry stools. Many people now define constipation as having less than 3 bowel movements per week. Constipation is thought to be caused by factors such as lack of fibre in the diet, lack of physical activity, lifestyle changes such as pregnancy, stress and ageing, and by dysbiosis.
Coronary heart disease is a condition of recurring chest pain. This happens when part of the heart is not receiving enough blood. Coronary heart disease is sometimes called Ischemic heart disease. Coronary heart disease usually develops when cholesterol particles in the blood start to collect in the arteries and stick to the artery wall. Eventually these deposits of cholesterol becomes hard and form plaques which may narrow the artery. This can then decrease blood flow and therefore the amount of oxygen which is supplied to the heart muscle. Signs and symptoms of coronary heart disease can either develop slowly or quickly. Some people have no symptoms at all, but more often than not people experience severe chest pain (angina) and a shortness of breath. This can of course pose a risk of a heart attack.
Crohn's is an inflammatory bowel disease (IBD) in which parts of the digestive tract become swollen and develop ulcers. Generally located in small intestine and/or colon, Crohn's can in fact develop anywhere in the gastrointestinal tract, from the mouth to the anus.
Cystitis is an infection of the bladder particularly affecting women, causing symptoms such as a burning sensation during urination as well as a frequent need to urinate. Cystitis is usually caused by pathogenic bacteria such as E. Coli entering the urethra and travelling to the bladder. Evidence suggests that maintaining healthy levels of friendly bacteria help promote balanced levels of vaginal flora.
Cytokines are cell signalling molecules that modulate the immune system response. Cytokines can either be peptides, proteins or glycoproteins, and they include the sub-groups: interleukins, in***feron and growth factors. Their main purpose is to initiate the movement of cells towards sites of either trauma, infection or inflammation.
Type 1 diabetes is an autoimmune condition, where the body's own immune system attacks the pancreas, the organ in the body that produces insulin. The resulting damage to the organ results in the pancreas being unable to produce enough insulin to regulate blood sugar levels in the body. Very high levels of blood glucose can be life-threatening, and so sufferers of this condition must inject insulin daily.
Diarrhoea is defined as frequent, loose and watery stools or bowel movements. Diarrhoea can be caused by numerous factors including food poisoning, IBS and Colitis. (Diarrhea is the American spelling)
Dietary fibre refers to indigestible components of fruits and vegetables. Dietary fibre is often classified into two groups:
Soluble fibre (including prebiotics) - which is digested by the microbes of the body and fermented in the colon, creating gas and physiologically active byproducts.
Insoluble fibre - aids defecation by absorbing water as it passes through the digestive system.
Taking place in the gastrointestinal tract, this term refers to the mechanical processing and enzymatic breakdown of foods into smaller parts which are more easily utilised and absorbed by the body.
Digestive enzymes are found in the digestive tract and aid in the breakdown of complex macromolecules such as carbohydrates and protein, into their smaller parts. These more simple molecules are then able to be absorbed and utilised by the body more easily. Digestive enzymes are secreted by glands throughout the digestive system including salivary glands which produce saliva and secretary cells in the pancreas and stomach.
Diverticulosis is a condition that can occur when the walls of the colon become weakened, sometimes due to long term constipation which exerts pressure on the walls of the gut. Diverticulosis refers to the formation of small pockets or pouches in weak points of the intestine; pouches known as 'diverticula'. Diverticulitis is the disease in which the diverticula (pouches) become inflamed or infected. Diverticulitis is much more common in older people.
Research suggests that having a healthy balance of friendly bacteria in the gut can reduce the risk of diverticulosis and diverticulitis.
A double-blind trial refers to a scientific experiment in which both the test subjects and the research team are prevented from knowing certain pieces of information (i.e which control group is taking a placebo) that may lead to conscious or subconscious bias - which would invalidate the results.
Also called dysbacteriosis, is a term for a microbial imbalance or maladaptation on or inside the body, such as an impaired microbiota.
Dysbiosis, Dys-symbiosis, or dysbacteriosis is the condition which describes an imbalance of beneficial and pathogenic bacteria in the body. (ie. too few beneficial bacteria in the gut.) Dysbiosis can be caused by factors such as travel, ageing, or taking antibiotics, which kill off both good and bad bacteria in the system. It is possible for people to take a particularly long or strong course of antibiotics at some point in their lives, and still suffer from dysbiosis many years later.
Dysbiosis is thought to contribute to a number of health issues including, but not limited to, IBS, food intolerances and allergies, weight gain, poor skin health, poor immunity, low energy levels, Candida and/or thrush.
The full name of this bacteria is Escherichia coli. It forms part of the normal bacteria of the lower intestines in many humans and is generally harmless. An overgrowth of some strains of E. coli bacteria can cause problems, such as urinary tract infections, food poisoning, diarrhoea and respiratory illness (including pneumonia).
Eczema is a type of dermatitis, which causes patches of skin to become itchy, red, dry and cracked. It is a long-term (chronic) condition in most people, although it can improve over time, especially in children. Eczema can affect any part of the body, but the most common areas to be affected are the backs or fronts of knees, outside or inside elbows, neck, hands, cheeks and scalp. Atopic eczema often runs in families and is linked to allergies. Gut dysbiosis has also been linked to eczema symptoms.
Endogenous means to originate or develop internally within an organism, tissue or cell. Endogenous bacteria are those which reside within a closed system such as bacterial gut flora which live in the gastro-intestinal tract - they are a natural part of the organism or microbiome.
The enteric nervous system is a part of the autonomic nervous system that is responsible for innervating and controlling the gastrointestinal tract and digestive processes. Also known as the intrinsic nervous system, it has been described as the 'second brain' and can function autonomously, although it requires communication with the central nervous system to function effectively.
The epithelium is the lining on most most internal and external surfaces of the humanbody. This type of tissue consists of one or more layers of tightly packed cells and lines the gastrointestinal tract as well as other parts of the body including the organs. It acts as a protective layer to help prevent toxins and pathogens from entering the body.
Endogenous means to originate or develop externally - from outside an organism, tissue or cell. Exogenous bacteria are those which come from the environment are are often pathogenic or alien to the system. As a result, they may induce an immune response or inflammation.
Firmicutes are the largest family of bacteria found in the human microbiome. They are anaerobic, so do not need oxygen to survive. The Lactobacilli and Clostridia species both belong to this family of bacteria.
Free radicals are molecules that are produced as part of natural bodily processes, such as energy production, as well as being a by-product of environmental and lifestyle factors, such as smoking and air pollution. A free radical is an unstable and highly reactive molecule and can therefore do damage to cells in the body. As a result, in high numbers they are thought to contribute to a range of diseases including cardiovascular disease, cancer as well as the aging process. Free radical damage can be minimised by the use of antioxidants.
Friendly bacteria is another name for probiotics (also known as good or beneficial bacteria). Friendly bacteria are defined as any bacteria that are beneficial to the body and enhance health.
Fructooligosaccharides (FOS) are one of the most well-known prebiotics, which are carbohydrates that provide food for the probiotic bacteria and thus help them to grow and colonise the intestines. FOS is derived from naturally occurring in foods such as chicory root. It has a slightly sweet taste and can be used as a natural sweetener instead of sugar. As humans, we can't digest or absorb FOS and it passes through our digestive tract to the large intestine where it acts as a food source for probiotics.
A fungus is a member of a large group of spore-forming organisms that range from microorganisms such as yeasts and moulds to the more familiar mushroom. They play a vital role in the decomposition of organic matter and the nutrient cycle.
The Gut-Associated Lymphoid Tissue, or GALT, comprises of several types of lymphoid tissue that work to protect the body from invasion. These lymphoid tissues include Peyer's patches, tonsils and adenoids.
GABA is an amino acid found in the brain, that functions as an inhibitory neurotransmitter. It has a calming effect on nerve impulses in the brain, making it a natural 'relaxation agent'. A deficiency of GABA can lead to feelings of anxiety, tension headaches and even reduced cognitive function as the nervous sytem becomes over-stimulated and agitated.
Referring collectively to the stomach and small and large intestines. The commonly used abbreviation for gastrointestinal is GI.
The gastro-intestinal tract, or simply 'gut', refers to the entire passage between a human's mouth and anus, including the oesophagus and stomach. This system of organs takes in food, digests it to extract energy and nutrients, and expels the remaining waste.
Gastro-oesophageal reflux disease (GORD), or simply acid reflux disease, is caused by stomach acids escaping the stomach into the oesophagus, causing mucosal damage of the oesophagus lining or chronic symptoms; the most common being frequent heartburn.
The condition usually occurs due to a spontaneous and unnecessary opening of the barrier muscles between the stomach and oesophagus. Possible reasons for this have been cited as; a hiatal hernia or abnormal relaxation of the lower oesophageal sphincter.
Gastroenteritis, or gastric flu, is an infection of the gut (usually the stomach or intestines). The infection can be viral, bacterial or parasitic; and is often caused by consumption of contaminated food or drinks. Symptoms include diarrhoea, abdominal cramping, bloating, nausea and vomiting.
Having a healthy balance of friendly bacteria in the gut is thought to lessen the risk of gastroenteritis, as well as relieving symptoms and quickening recovery.
A genus is a group of related or similar organisms, and can be referred to as a 'family'. A genus contains one or more species. Examples of probiotic genera include Bifidobacterium and Lactobacillus.
Gluten free means that a product does not have any gluten-containing ingredients. Gluten is a family of proteins (primarily glutenin and gliadin) found in grains such as barley, rye, wheat and oats, which form a sticky substance and help to make dough elastic. Gluten causes an auto-immune reaction in people with coeliac disease. It is also thought to cause a reaction in people suffering from non-coeliac gluten sensitivity. All ProVen Probiotics products are gluten free.
Galactooligosaccharides (or GOS) are carbohydrates that form prebiotic fibre to feed the friendly bacteria (probiotics). GOS is naturally present in breast milk and is thought to help feed the friendly bacteria to help the development of the baby's microbiome. GOS can also be derived from the lactose in milk.
This group of bacteria are known as ‘gram-negative’ as they don’t change colour when coming into contact with a staining method known as Gram’s method. This method is used to classify different types of bacteria. Gram- negative bacteria usually have thin cell walls and include members of the E. coli genus.
This group of bacteria is known as ‘gram-positive’ as they change colour when coming into contact with a staining method known as Gram’s method. This method is used in order to classify different types of bacteria. ‘Gram-positive’ bacteria have a thick cell wall (made out of peptidoglycan) which take on the purple stain.
The gut-brain axis refers to the physical and chemical connections between your gut and brain. ... Neurotransmitters and other chemicals produced in your gut also affect your brain. By altering the types of bacteria in your gut, it may be possible to improve your brain health.
'Gut flora' refers to the microorganisms that live within the body's digestive tract, mostly comprised of bacteria, including both probiotics and pathogenic bacteria.
Refers mainly to foods and that most people eat less than they should. Fruit, vegetables, pulses, nuts and whole grains feed healthy bacteria. Avoiding highly processed foods which do not constitute being gut-friendly as they often contain ingredients that either suppress 'good' bacteria or increase 'bad' bacteria.
The bacteria live throughout your body, but the ones in your gut may have the biggest impact on your well-being. They line your entire digestive system. Most live in your intestines and colon. They affect everything from your metabolism to your mood to your immune system.
Gut integrity refers to the health of the structure of the intestinal lining. An impairment of this gastrointestinal lining increases the risk of developing GI diseases, food intolerances, inflammation in the body and infections. Gut integrity can be damaged by a number of things prominent in modern life such as antibiotics, parasites, unhealthy diet, and sugar.
Haemorrhoids, or piles, are swollen veins in the anal canal and rectum. Haemorrhoids can be external (occurring outside the anal verge) or internal (occuring inside the rectum). Symptoms of haemorrhoids include swelling, pain, itching, irritation, and bright red blood. Piles or haemorrhoids are thought to be caused by excessive straining during bowel movements; often due to constipation.
Factors such as increased fluid intake, more exercise, and eating high fibre diets are thought to help prevent the development of haemorrhoids.
HDL (high-density lipoprotein) allows the transportation of fatty substances such as cholesterol and triglycerides around the bloodstream. HDL is small and dense and contains the highest ratio of protein to cholesterol. It is often referred to as the 'good cholesterol' as people with higher levels of this lipoprotein tend to be at lower risk of heart disease. HDL carries cholesterol away from the organs to the liver where it is mixed with bile, broken down and passed out of the body in the stool.
Helicobacter pylori, usually just referred to as H. pylori, is a pathogenic bacteria that grows in the stomach and is the main cause of many ulcers and stomach inflammation. H. pylori can weaken the protective coating of the stomach, leaving it vulnerable to digestive acids and consequent irritation. Many people carry small amounts of the bacteria in their system to no ill-effect but lifestyle factors such as consumption of alcohol, coffee and smoking increase the risk of a H. pylori instigated ulcer.
Since childhood, we have been taught that bacteria are harmful to health. Although this information passed from one generation to another is correct, it is incomplete as good bacteria also exist. Helpful and harmful types of bacteria are both present but very few people know about the beneficial bacteria.
The human immune system is a complex system of cells, processes and biological structures that protects the body from pathogenic microorganisms. The mucosal lining of the gut, which is maintained by probiotics, plays an important part in this system and is considered the front line against disease.
Short for irritable bowel syndrome. A widespread condition involving recurrent abdominal pain and diarrhoea or constipation, often associated with stress, depression, anxiety, or previous intestinal infection.
The human immune system is a complex system of cells, processes and biological structures that protects the body from pathogenic microorganisms. The mucosal lining of the gut, which is maintained by probiotics, plays an important part in this system and is considered the front line against disease.
The ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.
Immunomodulatory is where something such as a supplement, medication or chemical is capable of changing or modifying the immune response.
Caused by pathogens, which include bacteria, fungi, protozoa, worms, viruses, and even infectious proteins called prions. Pathogens of all classes must have mechanisms for entering their host and for evading immediate destruction by the host immune system. Most bacteria are not pathogenic.
Commonly known as ‘test tube’ experiments, these types of studies usually isolate components of an organism in an artificial laboratory environment so that certain factors can be more easily controlled. An example of this is in vitro fertilisation, whereby the egg is fertilised by sperm in equipment outside the body.
In vivo experiments involve complete living organisms such as animal studies and clinical trials involving humans. In vitro experiments are another type of research.
This occurs when the tissue lining the gut wall becomes damaged and allows certain substances such as toxins, microbes and undigested food to leak through the gut wall and into the blood stream. A healthy gastrointestinal system usually allows certain substances to pass through the gut wall such as water, vitamins and minerals but provides a barrier against other substances passing through. Increased intestinal permeability plays a key role in leaky gut syndrome.
Inflammation is part of a complex bodily response to infection or injury. This could be a mechanical, chemical, viral, bacterial, or biologic cause of damage. The body reacts with reddening, swelling, heat, pain and loss of function. The term inflammation is usually used with a specific area of the body in mind but is now often used to refer to the general increase in an ‘inflammatory state’ in the body. Inflammation is a natural and healthy response, however, persistent, systemic inflammation can lead to illness.
Inflammatory Bowel Disease (IBD) refers to both ulcerative colitis and Crohn's disease; both of which cause intestinal inflammation and symptoms such as abdominal pain, vomiting and diarrhoea.
Interleukins are a family of cytokines which are a group of naturally occurring proteins that are responsible for signaling between cells. Interleukins may regulate cell growth but they are particularly important in stimulating immune responses, such as inflammation.
Inulin is a prebiotic, and a natural polysaccharide (several simple sugars linked together) occurring in the roots and tubers of certain plants such as chicory.
Irritable Bowel Syndrome (IBS) is a functional disorder of the gastrointestinal tract characterised by varying symptoms such as bloating, abdominal pain or discomfort; accompanied by diarrhoea or constipation or alternation between the two.
The jejunum is part of the small intestine which lies between the duodenum and the ileum. The jejunum alone is roughly 9 feet in length, and is key in the absorption of nutrients during digestion.
Kefir is a thick, fermented milk originating from the Caucasian mountains, made with kefir grains; a combination of bacteria, yeast and polysaccharides. Kefir is often referred to as a 'probiotic' as it is thought to contain bacteria and yeasts that are beneficial to the body. Officially a probiotic or not, we would say that it is certainly a rich source of natural live cultures.
Lactic acid is an organic acid involved in many biochemical processes and produced by bacterial fermentation of carbohydrates. Lactic acid bacteria, or LAB, are a group of gram-positive bacteria that ferment sugars into lactic acid. This acid then makes it difficult for other bacteria or microorganisms to grow and thus inhibits the growth of potentially pathogenic bacteria.
Lactobacillus (singular) or Lactobacilli (plural) is a family (genus) of bacteria that includes strains such as acidophilus or paracasei. Lactobacillus bacteria convert sugars to lactic acid and tend to reside in the small intestine and genito-urinary tract. In women of European ancestry, Lactobacillus species are normally a major part of the vaginal microbiota and is also the most common bacteria found in food such as yoghurt.
Lactobacillus acidophilus is one of the primary strains of Lactobacillus bacteria
Lactobacillus paracasei is a species of probiotic that belongs to the Lactobacilli genus and is one of the four strains in the Lab4b group of bacteria found in the ProVen Probiotics pregnancy and baby products. This strain of Lactobacillus paracasei is naturally present in a baby's developing gut.
Lactobacillus plantarum is a member of the Lactobacillus family of bacteria, which is commonly found in fermented foods such as sauerkraut, and was first isolated from saliva. It is a natural resident of the human gastrointestinal tract and a strain of Lactobacillus plantarum has recently been added to the Lab4 group of bacteria to produce Lab4P, which has been shown to help support weight loss.
This species has been connected to IBS (although we would always stress the importance of strain-specificity) - in that a certain strain of Lactobacillus plantarum has been well researched in IBS sufferers. Other strains of the plantarum species have been researched in other groups of people, for example the strains CECT 7527, CECT 7528 and CECT 7529 have been tested and shown to help maintain healthy cholesterol levels.
Lactobacillus reuteri is a research-backed strain of Lactobacillus bacteria that occurs naturally in the digestive system of many people and forms part of a number of probiotic products. ProVen Probiotics CardioPro product contains one strain of Lactobacillus reuteri, identified by the strain number NCIMB 30242.
The large intestine is the final part of the gastrointestinal (GI) tract or gut. Its primary function is to absorb water and to eliminate undigested food from the body in the form of faeces. It is around 1.2 metres long and includes hte colon, rectum and anus. When it is working optimally, food will remain in the large intestine for around 18 hours. The large intestine hosts huge numbers of bacteria dominated by Bacteroides species.
LDL, or low-density lipoprotein, is a compound known as a carrier, that carries cholesterol around the body. As cholesterol is a fatty substance and cannot dissolve in the blood, it requires a carrier to transport it around the body. LDL particles tend to be less dense than other lipoproteins and as a result are also known as 'bad cholesterol' due to their ability to deposit fat molecules in cells walls, which can which can cause a build-up, leading to blocked arteries (atherosclerosis).
This is a term which is used to describe increased intestinal permeability in the lining of the digestive system. Leaky gut syndrome is a condition where the lining of the digestive system is impaired and damaged and therefore lets substance such as microbes, undigested food and toxins leak through the gut wall. This condition can impact negatively on digestion and is also thought to play a role in the development of certain autoimmune conditions. Although leaky gut syndrome is not completely understood, it is thought that factors such as stress, alcohol consumption, dysbiosis and the overuse of certain pharmaceuticals may play a role.
Live cultures and live bacteria are alternative names for probiotics or friendly bacteria. These terms all refer to beneficial microorganisms which are found naturally in the gut and some foods, including fermented foods such as yoghurt and sauerkraut. They are also found in probiotic supplements and include strains such as Lactobacillus acidophilus and Bifidobacterium bifidum.
The term metagenome refers to the genetic material which is present in a sample taken from the environment, and is made up of the genomes (genetic information) of an array of individual microorganisms.
Also known as methanogens, these types of organisms produce methane as a by- product of their metabolism, which among other things, contributes to flatulence production in humans. They thrive in low oxygen environments such as the human gut.
A microbe is a tiny microscopic organism, such as a bacterium, fungus or virus. There are trillions of microbes in the human microbiome.
A vast army of microbes that protect us against germs, break down foods to release energy, and produce vitamins to keep us healthy.
A microbiome encompasses the entirety of microbes in a defined habitat, including all of their genetic make-up and their environmental interactions. For example; a human microbiome (all of the microbes that we share our body with) includes approximately 100 trillion microbes, outnumbering our own cells by 10 to 1.
The gut microbiota is with humans from birth and affects function throughout the body. The human microbiota consists of a wide variety of bacteria, viruses, fungi, and other single-celled animals that live in the body. The microbiome is the name given to all of the genes inside these microbial cells.
'Microbiota' refers to the microorganisms (both probiotic and pathogenic) residing in the gastrointestinal tract. An imbalance in the microbiota is known as dysbiosis.
Microflora generally refers to the microorganisms (including both good and bad bacteria) that reside in the digestive tract. As the term 'flora' refers to plants, however, the term microbiota is now considered to be more correct than microflora.
The international standard way of measuring blood glucose levels are in terms of a molar concentration, measured in mmol/L.
Mucosa, also known as the mucous membrane, refers to the moist lining of internal, hollow organs such as the mouth and gastrointestinal tract.
The term 'mycobiome' refers to the fungal populations in a given environment. Studies have demonstrated the existence of diverse fungal colonies throughout the human body, and suggest their importance in both health and disease. There are many different genera of fungi, including: Candida, Fusarium, Cladosporium and Aureobasidium.
The nocebo effect is where an inert substance has a detrimental effect on human health. These are thought to be due to psychological or psychosomatic factors, which trigger actual biological reactions.
An observational study is a study in which a researcher observes behaviour in a structured manner, without actually being able to influence or interfere with the behaviour. Like with experiments, observational studies attempt to find the cause and effect relationship. Cohort studies and case-control studies are two main types of observational studies that help to evaluate associations.
Omega 3 is a type of polyunsaturated essential fatty acid which cannot be made by the body therefore we rely on dietary sources for our required intake. Omega 3’s are needed for many of the body’s processes, and are important for brain and heart health. They are made up of 3 types of fat known as EPA (Eicosapentaenoic acid), DHA (Docosahexaenoic acid) and ALA (Alpha Linolenic acid). EPA and DHA can be found in fish and some plants oils, and ALA is found only in plant oils.
Oxidative stress is the imbalance between the speed of production of free radicals (an oxygen-containing molecule that is very reactive with other molecules), and the body’s ability to counteract the harmful effects of these by producing protective antioxidants.
Are bacteria that cause disease. See also Infectious diseases.
Pathogenic bacteria, or pathogens, are harmful bacteria that cause disease or illness. Well-known pathogens include Salmonella or most types of E. coli.
Phagocytes are a type of white blood cell which play a vital role in the functionality of the immune system. Phagocytes perform the specific role of ingesting and absorbing pathogens or toxins, and can also release enzymes to destroy them. Once a phagocyte has engulfed a pathogen, it can communicate to other immune cells, such as lymphocytes, to help identify the type of antibody needed to neutralise invading pathogens.
This is one of the categories used in the biological classification of organisms and is ranked below kingdom and above class. It is a scientific hierarchy used to help arrange similar types of organisms together. For example, members of the genus known as Lactobacilli belong to the Firmicutes phylum.
A pilot study is a small study, experiment, or set of observations which are undertaken in advance of a planned large-scale project. It is used specifically to test aspects of the research design and to evaluate feasibility in advance of the project. This allows adjustments and improvements to be made prior to its start.
A placebo-controlled study is a clinical experiment in which the test subjects are split, usually, into two different control groups. One group will receive the medicine or supplement being trialled and the other will simply receive a placebo (a capsule, tablet, powder or liquid identical in appearance to the medicine or supplement being trialled but designed to have no measurable health effect). In most cases, placebos are used in blind trials where the control groups do not know if they are receiving the placebo or the real treatment.
Plasma is one of the main components of blood. 55% of blood volume is made up of plasma. Plasma itself contains a mix of proteins (Albumin, fibrinogen and immunoglobulins), salts and hormones.
Polyphenols are naturally occurring compounds, some of which are known to protect cells against the damaging effects of free radicals (therefore giving them antioxidant properties). They are broadly categorised into 4 mains groups; phenolic acids, stilbenes, lignans and flavanoids. Flavonoids are further classified into several groups. Flavanols, one of the group of flavonoids most abundantly found in fruit and vegetables, is made up of catechins and proanthocyanins, such as Grape Seed Extract.
Certain polyphenols are either specific to a particular food (e.g flavanones found in citrus fruit, resveratrol in red wine) and others are found in all plant foods (e.g quercetin is found in fruit, vegetables, cereals, legumes, tea & wine).
Research suggests that polyphenols, with their antioxidant properties, may play a role in the prevention of diseases, particularly relating to cardiovascular health and cancer prevention.
Pouchitis, with symptoms such as diarrhoea and abdominal pain, is an inflammation of the ileoanal pouch, a bowel pocket created to hold bowel movements in patients with ulcerative colitis who have had their large intestine or colon removed. Whilst antibiotics are often used as treatment for pouchitis, research shows that people with pouchitis have lower levels of beneficial bacteria in their system.
Are compounds in food that induce the growth or activity of beneficial microorganisms such as bacteria and fungi. The most common example is in the gastrointestinal tract, where prebiotics can alter the composition of organisms in the gut microbiome.
Prebiotics such as Fructooligosaccharides (FOS) can be found naturally in certain foods such as leeks and chicory root. Prebiotic fibres are a food source for probiotics to grow, multiply and survive in the gut; in particular stimulating growth of probiotics from the Bifidobacteria genus.
Members of this gram-negative genus are closely related to bacterioides, and are commonly a cause of wound infections in cat and dog bites. In humans, they exist as opportunistic organisms which are implicated in periodontal disease and anaerobic (absence of oxygen) respiratory tract infections such as pneumonia.
Are live bacteria and yeasts that are good for you, especially for your digestive system. We usually think of these as germs that cause diseases, but your body is full of bacteria, good and bad. Probiotics are often called "good" or "helpful" bacteria because they help keep your gut healthy. You can find probiotics in supplements such as tablets, powder and some foods, like yoghurt.
Probiotics are microorganisms, usually bacteria, that have proven health benefits - for the digestive and immune systems in particular. Different probiotic strains have been shown to demonstrate different beneficial effects on the body. Although probiotics are commonly referred to as 'friendly bacteria', probiotics can be other microorganisms, for example the probiotic yeast, Saccharomyces boulardii.
Most probiotics are sold as dietary supplements, which do not undergo the testing and approval process that drugs do. Manufacturers are responsible for making sure they are safe before they are marketed and that any claims made on the label are true. But there is no guarantee that the types of bacteria listed on a label are effective for the condition you are taking them for. Health benefits are strain-specific, and not all strains are necessarily useful, so you may want to consult a practitioner familiar with probiotics to discuss your options.
These are simple, single-celled organisms that do not have organelles or other internal membrane-bound structures. Critically they do not have a nucleus so only contain a single chromosome.
This is a preventative measure used to help protect against or avoid a disease or condition occurring. For example, probiotics can be taken prophylactically to prevent food poisoning when travelling to a high risk area.
Also known as ‘purple bacteria’, this term refers to a major phylum of gram- negative bacteria which include pathogens such as E.coli and salmonella.
Probiotic bacteria that either directly or indirectly influence the gut-brain axis and confer a benefit to mental health.
When referring to clinical trials, randomised refers to a trial which is set up in a deliberately random or unpredictable way. Known as the gold standard of clinical trials, randomised controlled trials ensure that the participants in the study are allocated randomly to the study groups.
Inflammation of the mucous membrane of the nose, caused by a virus infection (e.g. the common cold) or by an allergic reaction (e.g. hay fever).
Saccharomyces boulardii (or S. boulardii) is a unique probiotic yeast originally extracted from lychee fruit. It has a different biological make-up and differing actions from other probiotics species such as Lactobacillus acidophilus. Saccharomyces boulardii has undergone rigorous clinical research demonstrating its ability to bind to and flush out pathogens in the body. Newer research shows that Saccharomyces boulardii has strong anti-inflammatory properties.
Serotonin is a neurochemical and hormone found in the brain, intestines, and blood platelets. It is believed to play a key role in emotional behaviour and moods, and is often attributed to happiness. Many people do not know that most of the body's serotonin is located in your gut.
Short bowel syndrome (SBS) usually occurs when part of the small intestine has been removed for surgical reasons, such as to treat necrotising enterocolitis or Crohn's disease. On the other hand, infants can sometimes be born with a congenital short bowel. Symptoms include severe diarrhoea, cramping, bloating and fatigue. No cure is currently known for short bowel syndrome. As most absorption of food and nutrients occurs in the small intestine, people with short bowel syndrome are unable to absorb sufficient volumes of water & nutrients from food to sustain life.
We do not recommend probiotics containing Lactobacillus acidophilus Rosell-52 for infants for those with Short Bowel Syndrome.
These are a type of fatty acid which are produced by bacteria in the large intestine by the fermentation or breakdown of substances such as dietary carbohydrates. They are used by the body to produce energy and are metabolised in the liver and muscles.
Small Intestinal Bacterial Overgrowth (SIBO), also known as Small Bowel Bacterial Overgrowth (SBBO), refers to a condition in which abnormal amounts of pathogenic bacteria are present in the small intestine. It is generally caused by a lack of muscular activity in and around the small intestine, meaning that bacteria is not swept away into the colon as it should be. SIBO is associated with various digestive or even muscular conditions, including diverticulosis. Symptoms of SIBO include bloating, vomiting and diarrhoea.
'Species' refers to a type of microorganism existing within a genus or family. For example, acidophilus is the name of a species within the Lactobacillus genus. Different species within the same genus (eg. acidophilus and rhamnosus) are generally considered to be more closely related to each other than species from other genera (for example acidophilus is not closely related to the infantis species in the Bifidobacteria genus).
Various probiotic manufacturers use probiotics from the same genus and species, however one should always note the different strains used as well.
A group of prescription medicines that aim to lower the levels of LDL (‘bad’) cholesterol in the body. Statins are often offered to those with a history of heart disease or genetically high cholesterol. There are several different statin brands, such as Lipitor and Lipistat.
Statins are sometimes associated with a number of side effects so there may be advantages to trying to reduce cholesterol levels in other ways, such as by increasing intake of omega 3 fatty acids in your diet.
Statistical significance in research is a measure used to determine the importance and relevance of data results. In research the p-value is used to determine if the result from the research is statistically significant or to determine the reliability of the findings. So if the p-value is <0.05 then the result/data is statistically significant.
This is another term for faeces, the solid waste produced in the colon, which is eliminated from the body through the rectum. Stool consists of undigested food, water, dead cells, bodily substances and bacteria.
A probiotic 'strain' is a specific biological variety of a species. For example, although many probiotic products contain the species Lactobacillus acidophilus, different manufacturers use different strains of acidophilus; and it is therefore important to select a robust, clinically-trialled strain. In the probiotic 'Lactobacillus rhamnosus Rosell-11' Lactobacillus is the genus, rhamnosus is the species, and Rosell-11 is the specific strain.
In probiotics, a strain refers to a certain variant within a species. An example of a species is 'acidophilus', and an example of an acidophilus strain is 'Rosell-52'. The strain tells you where a particular probiotic originated, what it was cultured on, and arguably the most important factor; what research has been conducted on that particular probiotic variant.
Therefore 'strain-specificity' refers to the concept that the different effects of probiotics are variable right down to the level of the strains (and not just different families or species of bacteria). This argument hence states that any health benefits from probiotics should be acknowledged right down to a particular strain.
The dictionary definition of a supplement is ‘Something added to complete something else, make up for a deficiency, or extend or strengthen the whole’. Relating this definition to the field of natural health we can say that the goal of dietary supplements is to ‘make up’ for dietary deficiencies and ‘strengthen’ health. Food or dietary supplements can comprise either: vitamins and minerals, herbal extracts, essential fats, enzymes, amino acids or probiotics/live cultures.
Symbiotic means having an interdependent relationship (living in symbiosis). It generally refers to a biological interaction between two different organisms, known as symbionts, which may be of the same or different species. The relationship between the organisms may be of benefit to each type.
A synbiotic is a dietary supplement that combines both probiotics and prebiotics, which then work in synergy (hence SYNbiotic) with each other to help enhance the growth of beneficial organisms and inhibit the growth of pathogenic bacteria.
A systematic review is a literature review which analyses a collection of papers and research on a subject. They are usually based on questions which are set before the paper is written. A systematic review is designed to provide a complete and thorough summary of the current literature on a research subject.
Tablets are manufactured by compressing and compacting ingredients together. They are suited to supplements that require a large number or amount of ingredients, which often cannot be fitted into a capsule.
Transient refers to something that is temporary or remaining for a short period of time. Probiotics are considered to be transient as they are constantly excreted in faeces. Around 50% of our faecal mass is made up of bacteria, reflecting the dynamic nature of the microbiome and the potential that probiotics have to influence its composition.
Triglycerides are the main type of fat found in humans - they are the end-product of digesting and breaking down the fats in the food we eat. They are found in the blood and used by the body for energy. They are also used as a marker for heart disease - triglyceride levels above 200 are considered high, Factors affecting triglyceride levels include being overweight, smoking, excessive alcohol and some genetic disorders.
Ulcerative Colitis is an inflammatory bowel disease (IBD) which provokes inflammation and sores, or ulcers, in the lining of the large intestine (the colon and rectum). Symptoms of ulcerative colitis include abdominal pain/cramps, diarrhoea that contains blood or pus, rectal pain and nausea.
Urinary tract infection (UTI) is a bacterial infection that affects part of the urinary tract - a kidney infection affects the upper urinary tract and a bladder infection affects the lower urinary tract. E. coli is the most common UTI-causing bacteria. The symptoms include a burning sensation on urination and feeling the urge to urinate often.
The urogenital tract (also referred to as the ‘genitourinary system’) combines all the organs of the reproductive system and the urinary system. Namely the kidneys, ureter, bladder and urethra, plus the ovaries, fallopian tubes, uterus and vagina in women, and testes, prostate, seminal ducts and penis in men.
Thrush is a common yeast infection that affects both men and women. Vaginal thrush is yeast infection, known as Candida albicans, which has overgrown in the vagina and surrounding area. Symptoms of vaginal thrush include mild to severe itching and soreness in and around the vagina.
The vaginal microbiome is the bacteria that resides in the vagina. These bacteria form part of the overall human microbiome and help to support the health of the vagina, preventing pathogenic bacteria from causing infection in this area of the body. Lactobacillus are the main species of bacteria found in the vagina of healthy women.
A virus is the smallest type of infectious microbe that exists, being about 1/100th of the size of an average bacteria cell. A virus can only replicate itself inside the living cells of an organism (animal, plant or bacteria). Examples of viruses include the norovirus and Ebola.Symp
Yeasts are single-celled microorganisms that are members of the fungus family. They form part of the normal human microbiome, although some strains may be pathogenic if allowed to overgrow (see Candida albicans).
Saccharomyces boulardii is a 'friendly' yeast strain that has been shown to have beneficial characteristics, particularly in relation to diarrhoea.