Probiotics: A Comprehensive Guide. What Are They? Do They Work?

This article looks at the different types of Probiotics and their strains and details their possible uses as a health supplement.

Academic studies are also highlighted that discuss the benefits, or otherwise, of Probiotics and their possible side-effects.

What are Probiotics?

Probiotics are promoted as providing health benefits, particularly in restoring the natural balance of bacteria in the gastrointestinal tract, intestines and the stomach.

Probiotics are actually microorganisms consisting of live bacteria and yeasts and are either added to yoghurts or taken as a separate food supplement in liquid, powder, tablet or capsule form.

The companies that sell such products, often describe Probiotics as “good” or “friendly” bacteria.

Probiotics do occur naturally in some foods, including live yoghurts, milk kefir, miso soup, fermented soft cheeses, kimchi and sauerkraut.

There is more than one type of Probiotics with each having different characteristics and containing different strains of bacteria.

The two most commonly used Probiotics are Lactobacillus Acidophilus and Bifidobacterium, with the former recommended for lowering the incidence of antibiotic-associated diarrhoea, and the later recommended for IBS sufferers to reduce stool frequency, bloating and cramps.

Probiotics do depend on other live bacterial and yeasts, called Prebiotics, in order to provide the most benefit.

Prebiotics are non-digestible plant fibres that the body finds difficult to absorb and act as food for probiotics.

Typical Prebiotic foods are garlic, onion, bananas, asparagus, oats, barley, leeks and those containing resistant starch.

So, Probiotics and Prebiotics work together to provide a healthy digestive system.

The different types of Probiotics

There are a number of different Probiotic organisms and each type can be used to address different conditions in various parts of the body.

The two most common Probiotics groups are Lactobacillus and Bifidobacterium and these also have different strains. Other probiotic types include Bacillus, Streptococcus and Saccharomyces Boulardii (also called Saccharomyces Cerevisiae).

Saccharomyces Boulardii, which often goes under the brand name of Florastor, is a strain of Baker’s Yeast.

The table below shows the different types of Probiotic strains and some of the recommended uses of each type.

Lactobacillus, Bifidobacterium, Bacillus and Streptococcus strains have been used for a variety of different ailments and the most common ones are included in the table.

Probiotic TypeStrainUse to Treat/Improve
LactobacillusAcidophilusDigestion, Diarrhoea, IBS, Crohn’s Disease, Bacterial Dysbiosis
FermentedDigestion, Immune Response, Liver Health, Cholesterol Levels
PlantarumDigestion, Immune Response
RhamnososDiarrhoea, Vaginal Health, Crohn’s Disease, Lactose Intolerance
SalivariusOral Health, Mastitis, Colitis, IBS, E Coli, Salmonella
ParacaseiLiver Health
GasseriDiarrhoea, Vaginal Health, Obesity
ReuteriDigestion, Oral Health, Immune Response
BifidobacteriumBifidumDigestion, Diarrhoea, IBS, Lung Health
LongumDigestion, Immune Response
BreveDiarrhoea, Allergies. Skin, Obesity
InfantisDiarrhoea, IBS, Colitis, Psoriasis
BacillusCoagulansDiabetes, IBS, Arthritis, Vaginal Health
SubtilisDigestion, Obesity, Diabetes
StreptococcusSalivarius K12Oral Health, Immune Response
Salivarius M18Oral Health
ThermophilusSkin, Lactose Intolerance, Diarrhoea, Oral Health
Baker’s Yeast
(not a Probiotic)
Saccharomyces BoulardiiDiarrhoea, IBS, Urinary Tract Infections, Acne


The table above shows typical uses and treatments for each type of Probiotic.

This is not an exhaustive list as these Probiotics have been used by some people for the treatment and prevention of a whole range of other conditions which are detailed in this section.

Lactobacillus is a type of bacteria that normally live in the human digestive, urinary and genital systems although it is not disease causing.

As a Probiotic, it is mainly used for the treatment and prevention of diarrhoea, including infectious types such as rotavirus diarrhoea in young children and traveller’s diarrhoea.

Lactobacillus is also used to prevent and treat diarrhoea caused by using antibiotics.

Lactobacillus has also been used by some people for the treatment of digestion problems, Crohn’s disease irritable bowel syndrome (IBS), colon inflammation, colic in babies and for a condition called necrotising enterocolitis, which is a serious disease that affects the intestines of premature babies.

Other uses have been for treatment of Helicobacter Pylori which is the cause of most stomach and duodenal ulcers.

In addition, Lactobacillus has been used to treat urinary tract infections (UTIs), infections caused in people on ventilators, vaginal yeast infections in women, respiratory infections in children attending day-care centres, prevention of the common cold in adults and to boost the immune system.

Other uses include treatment for Lyme disease, lactose intolerance, high cholesterol plus treatment for hives, allergic dermatitis, eczema, acne, canker sores and fever blisters.


As the name suggests, is a type of bacteria that normally exists in people’s intestines, although this type of bacteria, which is lactic acid bacteria, can be externally produced and used as a Probiotic medication.

It is commonly used for the treatment of IBS, constipation, diarrhoea (including traveller’s diarrhoea and diarrhoea in babies) and for prevention of colds and flu.

Other uses have been for treatment of Helicobacter Pylori, which is the cause of most stomach and duodenal ulcers, and for airway infections such as the common cold in adults and children, as well as for ulcerative colitis of the bowel.

It is also used to minimize the death of good bacteria when patients are taking antibiotics.

Bacillus Coagulans

Is a type of bacteria that produces lactic acid and is often misclassified as lactobacillus, although it is used similarly to Lactobacillus and other probiotics.

People use Bacillus coagulans for the treatment of diarrhoea, including rotavirus diarrhoea in young children, traveller’s diarrhoea and to treat diarrhoea caused by using antibiotics.

Bacillus coagulans has also been used by people to treat IBS, general digestion problems, Crohn’s disease, ulcerative colitis, Clostridium Difficile Colitis and Helicobacter Pylori.

Other uses by people include for the prevention of cancer and cancer-causing agents, plus for the prevention of respiratory infections and for immune system health.

Bacillus Subtilis

is a spore-creating bacterium, that is usually found in the soil and the gastrointestinal tracts of sheep, cattle, goats and human beings.

It has also been used as an antibiotic alternative for poultry and livestock.

In humans, it supports digestion, enzyme production, and helps maintain a healthy gastrointestinal tract.

In addition, it helps decrease weight gain and protect against the creation of certain diabetic foot ulcers.

Streptococcus Salivarius

Is a non-pathogenic bacterial streptococcal species that is found in the human oral cavity and gastrointestinal tract.

It has anti-inflammatory properties and is used by people to improve oral health and to maintain a healthy immune system.

Streptococcus Thermophilus

Is a thermophilic lactic acid bacterium used in the manufacture of dairy products.

It is used by people to help alleviate lactose intolerance; to improve oral health; to treat chronic gastritis, and to alleviate diarrhoea.

Saccharomyces Boulardii

Is a yeast, which is a type of fungus and prevents the recurrence of diarrhoea caused by the bacteria Clostridium Difficile.

Saccharomyces Boulardii is also used by some people for general digestion problems, Crohn’s disease, IBS, ulcerative colitis and Lyme disease.

Other uses by some are for lactose intolerance, urinary tract infections, vaginal yeast infections, high cholesterol levels, hives and teenage acne plus for the treatment for eczema, acne, canker sores and fever blisters.

In the next section, there are details of clinical trials that have been carried out to show the effectiveness of each Probiotic in treating and preventing some of these conditions.

In addition, the next section also includes details of side effects and warnings in relation to taking these Probiotics.

Test Results and Side Effects


Probiotics have been tested by many laboratories to test the claims made by suppliers and manufacturers as well as to assess whether the labelling on products is correct.

In addition, tests have been carried out to ascertain the possible side effects of different probiotics and these have been listed in this section.

In 2007, a report in Scientific America by Ferris Jabir, entitled “Do Probiotics Really Work?”, concluded that although certain probiotics help treat some gut disorders, Probiotics have no known benefits for healthy people.

However, the report went on and stated that several combined analyses of dozens of studies have concluded that Probiotics may help prevent some common side effects of treatment with antibiotics.

A 2014 review by an independent network of experts working for Cochrane, found that Probiotics can be useful in a hospital’s neonatal intensive care unit in significantly reducing the likelihood of premature babies developing Necrotising Enterocolitis.

Researchers estimate that 12% of premature babies, weighing less than 3.3 pounds, will develop Necrotising Enterocolitis and that 30% of them will not survive.

Probiotics probably prevent the disorder by boosting the numbers of beneficial bacteria, which may deter the harmful ones.

In 2006, Jens Walter of the University of Alberta and his colleagues published a study to see what it would take to get the bacteria in a Probiotic to successfully colonise the intestines of 23 volunteers.

They chose a strain of Bifidobacterium Longum and the volunteers consumed either a drink containing 10 billion live Bifidobacterium Longum bacteria or a placebo.

Periodic faecal samples revealed higher than typical levels of Bifidobacterium Longum in participants who did not consume the placebo and the study concluded that their gut ecosystems had a vacancy that the Probiotic filled.

So, if a doctor knows that an individual with severe diarrhoea has an undersized population of a particular Probiotic, then prescribing the missing strain should increase the chance of a successful treatment.

A report in the Saudi Pharmaceutical Journal entitled, “Role of Probiotics in health improvement, infection control and disease treatment and management”, by contrast to other learned reports, concluded there were some health improvement benefits of Probiotics, as follows:

  1. Probiotics are useful and friendly microbes.
  2. They are able to compete with the bad microbes and colonise our digestive system.
  3. They are able to ferment our food into simpler by-products and could promote our health through many different mechanisms.
  4. Their amount could be deteriorated due to many factors, such as incorrect diet, alcohol, age and so on. This is why they should be taken through our regular diet.
  5. In particular cases such as after antibiotic treatments, where they are expected to be affected severely, they should be taken orally in considerable amounts or with food.
  6. Probiotics promote health while they:
    • Remove the side effect of the pathogens or the harmful microbes.
    • Supply the body with useful by-products.
    • Reduce the jobs of our digestive system.
    • Reduce the effect of the first attack of harmful compounds, instead of our cells, by their biofilm, which protects our digestive system.
    • Reduce the amount of food needed by our bodies due to the correct digestion and metabolism of any amount of food.
    • Probiotics in some cases could complement the deficiency in our genetic materials by helping us to borrow the products of their genes (such as in case of the lactose fermentation deficiency).

The report also produced a list of Probiotic strains that can be used in the treatment of certain diseases.

The table is as follows:

Disease NameStrain
EczemaEscherichia coli; Bifidobacterium bifidum; Bifidobacterium lactis; Lactococcus lactis
Food allergiesEscherichia coli
ImmunityBacillus circulans PB7; Lactobacillus plantarum DSMZ 12028
Antibiotic effect removalEnterococcus mundtii ST4SA Lactobacillus plantarum 423; Lactobacillus brevis KB290; Lactobacillus strains; Bifidobacterium strains
Gastroenteritis TherapeuticsLactobacillus casei
Intestinal hyperpermeabilityLactobacillus plantarum species 299 (LP299)
Vaginal candidiasis (thrush)Lactobacillus rhamnosus GR-1 Lactobacillus reuteri RC-14
Urinary tract infectionLactobacillus rhamnosus GR-1 Lactobacillus reuteri RC-14
Lactose intoleranceLactobacillus acidophulus
Non-steroidal anti-inflammatory drugEscherichia coli strain Nissle 1917
Intestinal dysbiosisLactobacillus johnsonii La1; Lactobacillus strain; Lactobacillus GG
Irritable bowel syndromeBifidobacterium infantis 35624; Escherichia coli DSM17252; Bifidobacterium infantis 35624
Traveler’s diarrheaLactobacillus GG; Lactobacillus plantarum
Radiation-induced diarrheaLactobacillus casei DN-114 001
Crohn’s diseaseEscherichia coli strain Nissle 1917
Prevention of colon cancerEnterococcus faecium M-74; lactic acid bacteria
Ulcerative colitisLactobacillus acidophilus; Escherichia coli Nissle 1917; Bifidobacterium
Peptic ulcer diseaseLactobacillus acidophulus
Prevention of atopyLactobacillus rhamnosus GG
Hypercholesterolemia and cardiovascular diseasesEnterococcus faecium M-74; Lactobacillus plantarum Propionibacterium freudenreichii; Lactobacillus plantarum PH04

In 2003, an in-depth study published in the Applied and Environmental Microbiology Journal by R. Temmerman, I. Scheirlinck, G. Huys, and J.

Swings, entitled, “Culture-Independent Analysis of Probiotic Products by Denaturing Gradient Gel Electrophoresis” tested 10 Probiotic yoghourt products, including Actimel and Activa, and found that the quality of many of theses probiotic products were misleading in terms of their contents and label information and six products were not found to contain all the claimed species shown on the label.

In 2013, an investigation by Margaret A Brinich, Mary Beth Mercer and Richard R Sharp published by BMC Gastroenterology entitled, “An Analysis of Online Messages about Probiotics” examined a sample of 71 websites presenting Probiotic information.

The study found that on commercial websites descriptions of the benefits far outnumbered the descriptions and number of the risks of taking the Probiotic, whereas on non-commercial websites more risks were included.

Side Effects

As regards the side effects of Probiotics, it very much depends on the state of health of the individual taking them.

The National Center for Complementary and Integrative Health (NCCIH), carried out a study and showed that a particular kind of Lactobacillus appears safe in healthy adults age 65 and older, however, the study concluded that this does not mean that all Probiotics would necessarily be safe for all people in this age group.

There are no studies of side effects for every Probiotic strain so if taking a particular one, any side effects should be reported to a medical practitioner.

For those that are generally healthy, Probiotics do have a good safety record.

Side effects, if they occur at all, usually consist only of mild digestive symptoms such as flatulence.

On the other hand, there have been reports linking Probiotics to severe side effects, such as dangerous infections in people with serious underlying medical problems.

The people who are most at risk of severe side effects include critically ill patients, those who have had surgery, very sick babies, and people with weakened immune systems

A number of studies have concluded that even for healthy individuals, there are uncertainties about the side effects of taking Probiotics.

Because many research studies on Probiotics have not looked closely at side effect aspects of all strains of Probiotics, there is not enough information right now to answer many side effect questions.

Most of the knowledge about side effects comes from studies of Lactobacillus and Bifidobacterium; although less is known about other Probiotics.

Information on the long-term side effects of Probiotics is limited, and side effects may differ from one type of Probiotic to another.

However, some of the side effects that have been reported are shown in the table below.

This shows typical side effects that may occur and is not particular to any type or strain of Probiotic.

The information in this table is based on an evidence-based study in 2017 by Erica Julson and her colleagues into the side effects of Probiotics, highlighted five possible side effects.

The conclusions are as follows:

Side EffectDescription
Unpleasant Digestive Symptoms


The most commonly reported reaction to bacteria-based probiotic supplements is a temporary increase in flatulence and bloating.

Starting with a smaller dose may prevent this.

Headaches due to Amines in Probiotic-Rich Foods


Foods such as kimchi, yoghurt and sauerkraut contain Amines.

Amines can excite the central nervous system, increase or decrease blood flow and may trigger headaches or migraines in some people.

Some Probiotic Strains can increase Histamine levels in the Digestive Tract







When histamine levels rise, blood vessels dilate to bring more blood to the affected area.

The vessels also become more permeable so that immune cells can easily get into the relevant tissue to combat any pathogens.

This process creates redness and swelling in the affected area, and can also trigger allergy symptoms such as itching, watery eyes, runny nose or trouble breathing.

Individuals with histamine intolerance should avoid such Probiotic strains.

Some histamine-producing probiotic strains include Lactobacillus buchneri, Lactobacillus helveticus, Lactobacillus hilgardii and Streptococcus thermophilus.

Some Probiotic Ingredients may cause Adverse Reactions



Such individuals should read the labels of Probiotic supplements carefully since they might contain ingredients they could react to.

Ingredients could include yeast, milk, sugar, lactose.

Some Probiotic supplements also contain Prebiotics and this can cause flatulence and bloating in some individuals.

The increase of Infection risk







In rare cases, the bacteria or yeasts found in probiotics can enter the bloodstream and cause infections in susceptible individuals.

It is estimated that only about one in one million people who take Probiotics containing Lactobacilli bacteria will develop an infection.

When infections do occur, they typically respond well to traditional antibiotics or antifungals.

However, in rare cases, deaths have occurred.

Research also suggests that people with severe acute pancreatitis should not take probiotics, as this may also increase the risk of death.


Research into the effectiveness of Probiotics and their side effects gives mixed results, but if an individual is completely healthy with no allergies, then there is no benefit in taking Probiotics.

Probiotics are living microorganisms that do provide health benefits for certain conditions.

Probiotics are safe for the majority of the population, but side effects can occur.

The most common side effect is a temporary increase in flatulence, bloating, constipation and thirst.

Some people can react to ingredients used in Probiotics and if this occurs, the supplement should not be used anymore.

Overall, probiotics are a beneficial addition to most individual’s diet or supplement regimen, with relatively few and unlikely side effects.

Care should be taken when reading labels and claims associated with commercially-advertised supplements as it has been shown that for some products, not all ingredients are listed and that the benefits of the products can be exaggerated and some possible side-effects not disclosed.