Probiotics, what are they and what types are there
Published: 11 September, 2023 | 10'
What are probiotics?
The intake of probiotics in our daily diet provides direct benefits to our intestinal flora or microbiota, maintaining it in balance and preventing intestinal imbalances such as diarrhea, flatulence, abdominal bloating, malfunction of the intestinal barrier affecting the immune system, among other consequences.
How are probiotics classified?
From a scientific point of view, the classification of any biological organism is the arrangement of organisms into taxonomic groups (taxa) based on similarities or relationships.
Taxonomy of probiotic organisms.
Probiotic organisms are classified according to their genus, species, subspecies, and an alphanumeric designation that identifies a specific strain, according to the World Gastroenterology Organisation2.
Denomination of different microorganisms.
An example of nomenclature applicable to microorganisms is: Lactobacillus (genus) casei (species) DN-114 001 (strain).
According to the guidelines of the WHO/FAO1, probiotic manufacturers must register their strains with an international depository, which assigns an additional designation to the strains.
The following table, taken from the World Gastroenterology Organisation Global Guidelines2, shows some examples of commercial strains and their corresponding names.
International strain depository designation
|* ATCC, American Type Culture Collection; CNCM, National Collection of Microorganism Cultures; NCIMB, National Collection of Industrial and Marine Bacteria|
What is a probiotic strain?
A strain is defined as a group of microorganisms, such as probiotic bacteria, that belong to the same species and share certain characteristics that are not found in other members of the species.
These characteristics may vary from one species to another, which means their effects can be different.
Importance of strain designation.
In the case of probiotics, it is important to use strain designations because the strongest approach to probiotic evidence is being able to attribute benefits to specific strains or combinations of probiotic strains at an effective dose2.
The FAO and the WHO propose that since probiotic properties are strain-specific, strain identification (genetic typing) should be performed using methods such as pulsed-field gel electrophoresis (PFGE) as well as genetic identification using DNA or RNA, or other internationally recognized methods.
CFU (Colony Forming Unit)
A CFU is a unit of measurement used to quantify microorganisms, i.e., to count the number of viable bacteria in a liquid or solid sample. Colony Forming Units are measured in units of volume (CFU/ml) or mass (CFU/g).
What is the viability of microorganisms?
The viability of a microorganism is defined as the ability to multiply under controlled conditions. The probiotic quality is primarily measured by the maintenance of viability (expressed as Colony Forming Units or CFU) until the end of the product’s shelf life, and the genus, species, and strain of all organisms included in the product should be identified.
Are all probiotics the same?
The FAO and the WHO have defined (see figure taken and translated from Pandey, 20154) a list of parameters that provides a systematic approach for an effective assessment of probiotics that substantiates health claims and benefits.
These parameters determine the obligations for developing probiotic products, which include the following activities:
- Strain identification.
- Functional characterization of the strain(s) in terms of safety and probiotic attributes.
- Validation of health benefits in human studies.
- Correct labeling of efficacy claims and content throughout the shelf life.
- The recommended dosage, which should be based on the induction of the declared physiological effect.
Types of probiotics
As mentioned, the probiotic potential of different bacterial strains, even within the same species, can vary.
This means that probiotic strains of the same species are always unique and can have different sites of action, as well as specific immunological effects, and can differ in their effects on both a healthy and inflamed intestinal system.
The most popular strains are represented by the following bacterial genera:
But other organisms, including
have also been used as probiotics.
Bacteria as probiotics.
Bifidobacteria are anaerobic Gram-positive (grow in the absence of oxygen), rod-shaped, non-gas producing, non-sporulating, and non-motile.
This genus includes 30 species:
- 10 of which are derived from human sources (dental caries, feces, and vagina),
- 17 from the animal intestinal tract or rumen,
- 2 from wastewater, and
- 1 from fermented milk.
Bifidobacteria are microorganisms of great importance in the gastrointestinal and genitourinary tracts, whose exact proportion is mainly determined by age and diet.
The number of bifidobacteria decreases as age increases and ends up becoming the third most abundant genus (representing approximately 25% of the total adult intestinal flora) after the Bacteroides and Eubacterium genera.
The clinical data in the following table mentions some of the positive actions of bifidobacteria.2
Antibiotic-associated diarrhea (AAD)
Bifidobacterium lactis Bi-07, B. lactis Bl-04, Lactobacillus acidophilus NCFM, L. paracasei Lpc-37
1.70 x 1010 CFU
Prevention of AAD in hospitalized patients
Irritable Bowel Syndrome (IBS)
Bifidobacterium infantis 35624
108 CFU, once daily
Improvement in overall assessment of IBS symptoms in subjects
Bifidobacterium bifidum (KCTC 12199BP), B. lactis (KCTC 11904BP), B. longum (KCTC 12200BP), Lactobacillus acidophilus (KCTC 11906BP), L. rhamnosus (KCTC 12202BP), and Streptococcus thermophilus (KCTC 11870BP)
2.5 x 108 viable cells once daily
Improvement of the elderly’s fecal microbiota
Prevention of nosocomial diarrhea
B. bifidum (1.9 x 108 colony-forming units [CFU]/g powdered formula: 35.8 x 108 CFU/100 kcal) and S. thermophilus (0.14 x 108 CFU/g: 2.69 x 108 CFU/100 kcal)
Infant formula, which was administered to infants as directed by the physician
Reduction in the incidence of acute diarrhea and rotavirus shedding in hospitalized infants
Lactobacilli are characterized by being Gram-positive bacilli or cocobacilli, non-sporulating, non-flagellated, able to grow in oxygenated or non-oxygenated environments, and strictly fermenting.
There are 56 species of the Lactobacillus genus that have been identified.
Lactobacilli are distributed along the gastrointestinal and genital tracts. Their distribution is affected by various environmental factors, such as pH, oxygen availability, level of specific substrates, presence of secretions, and bacterial interactions.
Positive Effects of Lactobacilli:
The table below shows some clinical results of the positive effects of lactobacilli.2,7
Treatment of acute diarrhea in adults
Lactobacillus paracasei B 21060 or L. rhamnosus GG
109 CFU, twice a day
Prevention of diarrhea associated with Clostridium difficile (or prevention of recurrence)
Lactobacillus acidophilus CL1285 and L. casei LBC80R
5×1010 CFU/day and 4–10×1010 CFU/day
Coadjuvant therapy for eradication of Helycobacter pylori
Lactobacillus reuteri DSM 17938
1×108, CFU three times a day
Reduction of side effects related to second-line therapy with levofloxacin
Effects on the immune system
L. plantarum 299v (DSM9843), L. plantarum HEAL 19 (DSM15313), L. fermentum 35D, L. paracasei 8700:2 (DSM13434), L. gasseri VPG44 (DSM16737) or L. rhamnosus 271 (DSM6594)
Stimulation of white blood cells (CD8+ and NK), suggesting that the intake of probiotic bacteria can improve immune defenses against, for example, viral infections.
Other probiotic bacteria:
The species of Bacillus have been used as probiotics for at least 50 years in an Italian product marketed as Enterogermina® (2×109 spores). Some advantages of bacterial spores are their resistance to heat, which allows them to be stored at room temperature and in a desiccated form.
Furthermore, these bacteria are capable of reaching the small intestine as they survive the acidic pH of the stomach.
The most studied species is B. subtilis, because its consumption in some probiotic products has shown evidence of stimulating the immune system, through action on the gut-associated lymphoid tissue and secretion of antimicrobial substances.
Among the species of Enterococcus, Enterococcus faecium is the most commonly used in probiotics. The presence of E. faecium is important in the prevention of infection by Salmonella enterica.
Interesting characteristics of the Enterococcus group are survival on dry surfaces for extended periods and resistance to antibiotics.
They are a group of unicellular fungi that primarily grow and ferment sugars. There are different families, but the most important from the point of view of nutrition and health are the so-called ascomycetes, which include the genus Saccharomyces, which are unicellular fungi that form spores and are heat resistant. Well-known examples are yeast for bread and beer.
Brewer’s Yeast, Sacharomices cerevisiae
The potential probiotic effect of S. cerevisiae and S. cerevisiae var. boulardii has been demonstrated, as they are able to tolerate the acidic environment and bile, and may have effects against bacterial infections by reducing intestinal proinflammatory response.
The table below shows clinical data of these effects.2,4,7
Treatment of acute gastroenteritis in children
Saccharomyces boulardii CNCM I745
250–750 mg/day (usually 5–7 days)
ESPGHAN/ESPID recommendations* 2014; ESPGHAN Probiotics Working Group. Meta-analysis of societies
H. pylori infection in children
Saccharomyces boulardii CNCM I745
500 mg (in two doses, for 2–4 weeks)
Reduction in the risk of side effects and increased eradication rate
Irritable Bowel Syndrome (IBS)
Saccharomyces boulardii CNCM I-745
5×109 CFU/capsule or 250 mg twice a day
Improvement in IBS-related quality of life score
Effects on the immune system
Saccharomyces boulardii CNCM I-745
Meta-analysis of 23 studies with 3938 children. 11% decrease in the relative risk of developing diarrhea, including diarrhea associated with C. difficile infection, and shorter duration of the disease in those who received probiotics.
* ESPGHAN: European Society for Paediatric Gastroenterology, Hepatology, and Nutrition; ESPID: European Society for Paediatric Infectious Diseases.
How are probiotics produced?
The manufacturing process of food-type probiotic products includes a series of stressing factors that challenge their potential benefit.
One of the most important is ensuring a high microbial load in the final product throughout its shelf life, and for this reason probiotics are first cultivated in large quantities, on an industrial scale, using appropriate culture media.
The second factor is that microbial inocula are usually stored frozen, to avoid subjecting them to low or changing temperatures.
Taking these factors into account, two drying techniques are generally used, spray drying and freeze-drying, which generate high-density probiotic powders that can be added to various types of food products, including dietary supplements.
• Spray Drying: It is a cost-effective technique that produces stable microbial powders with high cell populations. However, it often leads to a significant loss of cell viability due to the severe stress that especially affects the structure and functionality of probiotic cells, due to the high air temperature (evaporation of water in the drying chamber) and water removal.
• Freeze-Drying: This technique requires gentler conditions and is usually better tolerated by bacteria. Similarly, the process subjects the probiotic inoculum to very low temperatures and dehydration, which affect both bacterial or fungal integrity and viability. Likewise, the subsequent storage of dried probiotic biomass, loss of viability and activity is quite common. Probiotic products containing bifidobacteria are developed using either of these two techniques.
• Food Matrix: Another technique for producing food-type probiotics is especially for fermented products and their derivatives. It involves a direct inoculation into the food matrix that enables the growth of probiotic species through fermentation. This technique provides the advantages of avoiding the dehydration and inoculation steps in a different food matrix; however, the final product with incorporated probiotics may undergo variations depending on the specific composition and intrinsic physicochemical parameters of the food matrix itself, as well as its storage conditions. Probiotics containing lactobacilli generally use this technique for their production.
Strategies to improve viability of probiotic products.
The finding that probiotic products may have deficiencies in the number of truly viable cells, both in foods and dietary supplements, has prompted the development of new strategies to improve probiotic properties and response to stressors. Let’s see some of them.
It serves two purposes, to protect probiotics from gastric stress after oral intake, and to improve survival during the drying stages of manufacturing, and stability during storage in the finished food product. Chitosan and alginate are generally used as encapsulating agents.
Carrier media and protective agents.
The use of complex matrices, such as skim milk, significantly improves the survival and stability of probiotics, especially after drying and during storage.
The use of fibers from various plant sources enhances both the survival of probiotics during the drying process of the inocula and the storage stability of cells within food products. Fructooligosaccharides (FOS) are the most commonly used prebiotic ingredients for this purpose.
Addition of protective agents to counteract acidic pH.
Acidic pH is considered the main threat to probiotics, especially in the gastrointestinal tract. For this purpose, the addition of saccharides, amino acids, and fatty acids effectively protects probiotics against the acidic environment. This strategy is beneficial for probiotics containing yeasts.
Adaptation to stress and cross-protection.
In this strategy, bacteria are pre-exposed to sublethal levels of a specific stressor, which induces an adaptive response of increased resistance to subsequent doses of the stressor or even to a different type of stress. This process enhances probiotic survival.
Probiotic Dietary Supplements
There are probiotic dietary supplements available on the market that mainly contain strains of Lactobacillus, Streptococcus, Bifidobacterium, and yeasts (S. boulardii).
Probiotic dietary supplements are generally available in sachets, tablets, or capsules. There are three main factors that influence the viability of probiotic dietary supplements during storage: temperature, oxygen, and relative humidity.
Therefore, it is important to consider three aspects to ensure the viability of probiotics contained in dietary supplements:
- Store the products refrigerated, even if the label indicates that the cultures are stable at room temperature. In traditional lyophilization processes, increasing the storage temperature from 4 to 25 °C reduces stability by ten times.
- Close the container as quickly as possible after taking the supplement to reduce the entry of oxygen and moisture into the container. Many probiotic products design their storage formats with water-impermeable jar packaging or laminated packaging films, or by adding small moisture-absorbing sachets to the containers.
- If the container contains moisture- or oxygen-absorbing sachets, do not remove them. Oxygen is harmful to the viability of probiotics during storage.
- FAO/WHO Expert Consultation. Probiotics in Food: Health and Nutritional Properties and Guidelines for Evaluation. FAO and WHO, 2006. ISBN 92-5-305513-8.
- Guarner, F. & M. E. Sanders (chairs). World Gastroenterology Organisation Global Guidelines: Probiotics and Prebiotics. February 2017.
- Oak, S. J. and R. Jha. The effects of probiotics in lactose intolerance: A systematic review. Crit Rev Food Sci Nutr. 2019;59(11):1675-1683.
- Pandey, K. R. et al. Probiotics, prebiotics and synbiotics- a review. J Food Sci Technol (December 2015) 52(12):7577–7587.
- Plaza-Diaz, J. et al. Mechanisms of Action of Probiotics. Adv Nutr. 2019 Jan; 10(Suppl 1): S49–S66.
- Ross Watson, R. & V. R. Preedy. Probiotics, Prebiotics, and Synbiotics. 2016 Elsevier Inc. ISBN: 978-0-12-802189-7.
- Sharifi-Rad, J. et al. Probiotics: Versatile Bioactive Components in Promoting Human Health. Medicina (Kaunas). 2020 Aug 27;56(9):433.
- Soccol, C. R. et al. The Potential of Probiotics: A Review. Food Technol. Biotechnol. 48 (4) 413–434 (2010).