Not all probiotics are the same. Different probiotic strains have different characteristics and are studied for different uses. This guide explains how probiotics are classified, introduces common strains and shows what to consider when choosing a supplement.
🕒 6 min read
Probiotic strains at a glance
- A probiotic is identified by its genus, species and strain.
- Research on one strain cannot automatically be applied to another.
- More strains do not necessarily mean a better supplement.
- The right choice depends on the strain, dose, evidence and your individual needs.
Probiotics explained
The term probiotic is used for live microorganisms that are intended to provide a health benefit when consumed in an adequate amount.1 They are usually bacteria, although some probiotics are yeasts. They can be found in certain fermented foods and in supplement form.
Not every fermented food or live culture is automatically a probiotic. The exact microorganism, strain, dose and evidence all matter. For a broader introduction, read our guide to what probiotics are and how they work.
Important
Probiotic products and strains can have different effects. People with an existing health condition or a weakened immune system should speak to a doctor before taking a probiotic supplement.9
How are probiotics classified?
Probiotic microorganisms are usually identified using three levels of information:
Genus
The broad group the microorganism belongs to, such as Lacticaseibacillus.
Species
A more specific group within the genus, such as rhamnosus.
Strain
The precise variation within the species, often shown as a code or registered name, such as GG.
Together, these details identify the microorganism more precisely. This matters because research findings for one strain cannot automatically be applied to every strain in the same species.3
You may also notice different names in newer research. In 2020, scientists reclassified the former Lactobacillus genus into several new genera.2 For example, Lactobacillus rhamnosus is now formally called Lacticaseibacillus rhamnosus, while Lactobacillus plantarum is now Lactiplantibacillus plantarum. Many supplement labels and consumer guides still use the familiar older names.
What are the different probiotic strains?
Hundreds of probiotic strains are used in research and commercial products. The following species and strains are among those most commonly seen on supplement labels.
Lactobacillus acidophilus
Lactobacillus acidophilus is naturally found in the digestive and vaginal microbiota. Specific strains are used in yoghurts and supplements and have been studied in relation to digestive and women's health.
Benefits cannot be assumed across every product, so check the complete strain name where it is provided. Read more in our guide to acidophilus probiotic benefits for women.
Lacticaseibacillus rhamnosus
Often still labelled Lactobacillus rhamnosus, this species includes the well-known GG strain. Specific strains have been studied in relation to antibiotic-associated diarrhoea and other digestive outcomes, but efficacy varies by strain and condition.3
It is usually found in capsules, powders and some fermented products.
Lactiplantibacillus plantarum
Formerly known as Lactobacillus plantarum, this microorganism is found in fermented foods including sauerkraut and kimchi.
Some strains show useful tolerance to acidic conditions, which can help them remain viable during digestion, and different strains have been studied for digestive outcomes.4
Bifidobacterium bifidum
Bifidobacterium bifidum is commonly found in the human gut, particularly early in life. Research has explored how members of the Bifidobacterium genus interact with the intestinal barrier and immune system, although findings remain dependent on the species and strain studied.5
Find out more in our guide to the bacteria commonly associated with efficient digestion.
Bifidobacterium animalis subsp. lactis
This microorganism is often shortened to B. lactis on supplement labels. It is widely used in yoghurts, fermented milk drinks and probiotic supplements.
Individual strains, including HN019, have been studied for bowel frequency and intestinal transit, but those findings should not be generalised to every B. lactis product.6
Saccharomyces boulardii
Unlike most probiotics, Saccharomyces boulardii is a yeast rather than a bacterium. Specific preparations have been studied for reducing the risk of antibiotic-associated diarrhoea, although this does not mean every product is suitable for every person.7
Ask a doctor or pharmacist for advice before using a probiotic alongside prescribed treatment.
Streptococcus thermophilus
Streptococcus thermophilus is commonly used with Lactobacillus delbrueckii subsp. bulgaricus to ferment yoghurt.
Live yoghurt cultures can help improve lactose digestion in people who have difficulty digesting lactose, provided the product contains sufficient live cultures.8 This does not mean that every supplement containing S. thermophilus will have the same effect.
What are the best probiotics for gut health?
There is no single best probiotic strain for everyone. The best choice depends on why you are taking it, the exact strain or strain combination, the amount provided and the quality of the supporting human research.
Lactobacillus, Lacticaseibacillus, Lactiplantibacillus and Bifidobacterium strains are widely used in digestive-health research and supplements, but evidence for one strain should not be transferred to another.3
Our guides to the best probiotics for women and best probiotics for men provide more tailored information.
How many strains should a probiotic have?
More is not always better
There is no fixed number of probiotic strains that a supplement must contain. A well-characterised single strain or a smaller combination used at an appropriate dose may be more relevant than a long list of strains included without clear supporting evidence.
Look beyond the headline strain count and check whether the label gives full strain names, the number of colony-forming units and clear storage and usage instructions.
What should you consider when choosing a probiotic strain?
Choosing a probiotic involves more than comparing the number of strains. Consider the following:
Your reason for taking it
Look for a product containing strains that have been studied for the outcome that matters to you.
The complete strain name
A label that includes the genus, species and strain code gives you more useful information than the species name alone.
Number of CFUs
Colony-forming units indicate the number of viable microorganisms in a serving. The most useful dose is the one supported by evidence for the specific strain or combination, not necessarily the largest number on the shelf.
Shelf-life and storage
Follow the label carefully. Some products require refrigeration, while others are designed to remain stable at room temperature.
Format and packaging
Capsules, powders, liquids and gummies can all be formulated differently. Look for clear information about how viability is maintained through the end of the product's shelf-life.
Directions for use
Follow the product instructions. Timing can vary by formulation; our guide explains more about when to take probiotics.
For more help comparing products, read our guide to reading a probiotic label.
Finding the right probiotic
With many types of probiotics available, the right choice depends on the exact strains, dose, evidence and your individual needs.
Browse our full range of probiotic supplements, explore our digestive health range, or use the probiotic finder to compare suitable options.
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