What Are Probiotics?

  • Deepika Rana Bachelor of Dental Surgery(BDS), Dentistry , H.P.Government Dental College, IGMC Shimla.Himachal Pradesh, India

More than 100-300 trillion probiotic microbes are found in a healthy individual, although the human body only has 10 trillion cells. These days, probiotics, also known as "good" bacteria, are very popular in medicine. Curious about probiotics? How do they work? Are they efficient and safe to use? Together, let's address these queries in this piece.

Probiotics are foods and supplements that include beneficial microorganisms such as bacteria and yeast that colonise the gut and other body parts and provide numerous health advantages. 

Consider this article to learn more about the fascinating world of probiotics, how they can help you feel better, and how to include these healthy bacteria into your daily life.


The word "probiotic" was first used in 1953 by German scientist Werner Kollath to describe active substances essential for the healthy development of life. The word originates from the Latin pro and the Greek βιoσ (bios), which means "for life." Lilly and Stillwell first used this word in 1965, yet they did it in a different context to refer to substances secreted by one organism that allows another to develop. Specifically, Fuller (1992) described probiotics as a live microbial feed supplement that enhances the intestinal microbial balance of the host animal, hence benefiting it.

Beginning with the groundbreaking research of future Nobel laureate Elie Metchnikoff, a Russian scientist employed at the Pasteur Institute in Paris, the contemporary history of probiotics was written. According to Metchnikoff, adopt measures to alter our bodies' flora and replace harmful microbes with beneficial ones due to gut bacteria's dependence on food for survival. That provides a detailed explanation of the "probiotic concept." Still, given its strong kinship with the consumption of fermented foods, the history of probiotics extends back to human history.1

What are probiotics?

Microbial definition

Tiny living entities invisible to the human eye are called microorganisms. Because it includes both unicellular or tissue-free prokaryotes (bacteria and archaea) and eukaryotes (protists, microscopic algae, and fungi), the term "microorganism" is ambiguous taxonomically. Viruses are an exception to the rule that "microorganisms" only apply to entities with cellular organisation. When provided in sufficient amounts, probiotics and live bacteria offer health advantages to the host. The following genera of probiotic strains are beneficial: Bacillus, Escherichia coli, Saccharomyces, Enterococcus, Streptococcus, Bifidobacterium, and Lactobacillus.2,3

Functional definition

Helpful living bacteria called probiotics infiltrate the human gut and change the composition of the flora in specific areas of the host. They are crucial for the gut microbiota composition, assisting the host in forming a protective layer of healthy intestinal mucosa, improving the host's immune system, and preventing the colonisation of harmful bacteria in the intestine.4

Types of probiotics

Bacterial probiotics

Multiple pathogenic bacterial species are inhibited in their growth because they convert hexose sugars to lactic acid. These bacteria are a significant component of the lactic acid bacteria (LAB) group. Some of the first bacteria to colonise a newborn's gut after delivery are human Lactobacilli and Bifidobacterium. Fermented foods like wine, sourdough, pickles, yoghurt, and cheese develop with the help of certain Lactobacilli.

  • Bifidobacterium

Bacteria belonging to the genus Bifidobacterium are anaerobic, non-motile Gram-positives. They are endosymbiotic creatures that live in animals' vagina and digestive tracts, including humans. Bifidobacterium strains get used as probiotic bacteria due to their diverse resistance mechanisms to bile salts.

The genus of Gram-positive LAB called Lactococcus is widely employed in the dairy sector to produce fermented foods. Occasionally, they are suggested as probiotics as well.

Among the LAB used to produce yoghurt are the genera Streptococcus and Enterococcus.

Certain strains of the genus Bacillus are deemed probiotics for animal consumption, and some are lethal to humans. Though further research is necessary, Escherichia coli Nissle 1917 treats gastrointestinal disorders.

 Here is a visual depiction of the probiotic bacteria.

Gut microbiota     

Created by: Deepika Rana (Created with BioRender.com)

Yeast probiotics

S. boulardii acts as a probiotic in medicine to cure diarrhoea. S. cerevisiae for making wine, bread, and beer. S. bayanus is utilised to make wine. In addition, Saccharomyces yeasts work in symbiotic relations with bacteria to produce kefir, and they appear in kombucha.3

Fermented foods as natural sources

  • Kimchi and Gochujang (Korea)
  • Kefir (Russia)
  • Brem and Rusip (Indonesia)
  • Gundruk (India)
  • Wine (America)
  • Ergo (Ethiopia)
  • Garris (Sudan)5

Mechanisms of action

Primary mechanisms involve-

  • Probiotics function by binding to receptors on the intestinal mucosa and competing with pathogens for resources, making it more difficult for them to survive and stay there
  • Probiotics create anti-microbial compounds called bacteriocins, organic acids, and short-chain fatty acids (SCFA), which stop the growth of infections.
  • To prevent pathogens from passing from the intestine into the bloodstream and to support the integrity of the epithelial barrier, probiotics enhance the production of mucus and the expression of tight junction proteins.
  • Probiotics regulate the host's immunity by elevating the activity of T cells, which are essential for preserving immunological homeostasis and impacting the growth and functionality of dendritic cells 
  • The gut-brain axis is a way that probiotics can help the gut produce neurotransmitters. Serotonin, dopamine, and gamma-aminobutyric acid (GABA) levels are all modulated by probiotic strains having specific effects on gastrointestinal motility, mood, behaviour, and stress-related pathways 6

Created by: Deepika Rana (Created with BioRender.com)

Health benefits

Created by: Deepika Rana (Created with BioRender.com)

Effect on gastrointestinal disorders-

Probiotics enhance microbial diversity and richness, boost the synthesis of the enzyme lactase, enhance the immunological microenvironment, and improve intestinal permeability. The table below shows specific probiotics for treating digestive disorders.

Antibiotic-associated diarrhoeaLactobacillus, Lactococcus and Bifidobacterium
Radiation-induced and traveller’s diarrhoeaL. acidophilus and Bifidobacterium animalis
Ulcerative colitis Lactobacillus, Bifidobacterium and Saccharomyces boulardii 
Lactose intoleranceL.acidophilus
Irritable bowel syndrome (IBS)L. acidophilus, L. fermentum and S. boulardii 3,6

Antiallergic properties

Probiotics improve mucosal barrier functions, fortify the immune system, reduce antigen leakage through the mucosa, produce anti-inflammatory cytokines, increase the production of secretory IgA, degrade dietary antigens, and upregulate anti-inflammatory cytokines like IL-10 though the precise mechanism underlying these effects is unknown. Numerous Lactobacillus strains prevent allergic responses.6

Reduces anxiety and depression

The microbiome-gut-brain axis refers to communication between the neurological system and the gastrointestinal tract via gut microbes. By reducing systemic and intestinal inflammation and triggering the microbiome-gut-brain axis, probiotics may either directly aid in treating depression or, via the action of other gut microorganisms, lessen anxiety symptoms. Probiotics prevent bacterial overgrowth in the small intestine, reduce oxidative stress and inflammatory indicators, and boost the production of GABA and other neurotransmitters by microorganisms.12

Effect on obesity

Lowering blood cholesterol levels can be accomplished by using probiotics. Consumption of the L. plantarum strain reduced triglycerides and hepatic and serum cholesterol while raising the excretion of bile acids in the faeces. Combinations of probiotic strains of Bifidobacterium and Lactobacillus are better than others in improving metabolic disorders associated with obesity.6,13

Common ailments and probiotics 

During antibiotic treatment

Probiotic supplementation seems to maintain the level of Bifidobacteria during antibiotic therapy. Early adoption of probiotics by adults can safely and effectively prevent antibiotic-associated diarrhoea. Further study should focus on the optimal probiotic dosage and duration while considering strain specificity to generate modified medications.18,19

Probiotics in assigned females at birth (AFAB’s) health

Lactobacillus is the most prevalent bacterium in the vaginal mucosal barrier. It competes with pathogens to stop their colonisation by adhering to the vaginal epithelium. The vaginal microenvironment stability, immune system function, and potential to halt the spread of cervical cancer are all enhanced by probiotics.20

Pathogenic E. Coli is present in almost all recurrent urinary tract infections (UTI). Antibiotics used to treat these infections decrease the amount of lactobacilli in the urinary system, leading to antibiotic resistance later on and impairing natural defences against infection. Probiotic's capacity to attach to uroepithelial cells, prevent pathogenic growth, and secrete biosurfactants makes them a potential antibiotic therapy substitute. 

Vaginally administering the Lactobacillus probiotic chain is both safe and effective in avoiding recurrent UTI.21

Selecting and using probiotics

Matching the strain(s) with the targeted disease, the kind of formulation, the dose, and the supplier (manufacturing quality control and shelf-life) are all important considerations when selecting the right probiotic. Potential probiotic strains should possess desirable properties (4 A’s) for therapeutic effects. 

  • Acid and bile tolerance essential for oral administration
  • Adhesion to mucosal and epithelial surfaces is a critical characteristic for effective immune regulation, competitive exclusion of pathogens, and avoidance of pathogen adhesion and colonisation
  • Ability to fight microbes 
  • The activity of bile salt hydrolase

The probiotic dose levels efficient in human trials, with the colony forming units per gram of product, serves as a crucial criterion.14,15

Considerations and precautions

Probiotics have numerous health benefits, but to utilise them safely and effectively, you must be aware of a few factors and take precautions. The image displays the criteria used to evaluate the safety of probiotics.16,17

Created by: Deepika Rana (Canva) 

Speak to a medical expert before starting a probiotic regimen, particularly if you have specific health issues.


Are probiotics beneficial to the skin?

Probiotics play an integral part in photoaging management by inhibiting collagen formation. Studies revealed that individuals using Lactobacillus plantarum HY7714 displayed reduced epidermal moisture loss, lower wrinkle depth, and improved skin smoothness and gloss.7

How do probiotics and prebiotics differ?

Live bacteria offer health benefits to the hostNon-digestible food ingredients positively impact the host by selectively encouraging the growth and activity of a few bacteria in the colon that enhance health, as described by Gibson and Roberfroid. 
E.g. Yoghurt, cheese, wine and kimchiE.g. Barley, tomatoes, garlic, onions, wheat, honey, bananas, peas, and soybeans.8,9

Is it OK to take probiotics while pregnant?

Pregnant AFAB and their offspring can take probiotics without risk and with good tolerance. Its consumption has the potential to provide therapeutic and preventive benefits.10

Can probiotics effectively combat COVID-19?

Probiotics can treat COVID-19 as they stabilise the gut microbiota by controlling innate and adaptive immunity in the gut. Therefore, probiotics and their metabolites with established antiviral properties may act as a COVID-19 adjuvant treatment.11


Probiotic dietary supplementation can be a proactive move towards better health. These beneficial microorganisms, derived from food or supplements, offer advantages across different life phases, from early childhood to old age. Seek the advice of specialists for personalised guidance as you begin your road toward comprehending probiotics.


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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Deepika Rana

Bachelor of Dental Surgery(BDS), Dentistry , H.P.Government Dental College, IGMC Shimla.Himachal Pradesh

Hi, I am Deepika Rana Dentist by profession finished my Clinical Research Certification Programme from Duke NUS Medical school, Singapore in 2022. I joined Klarity’s internship because of my ongoing desire to learn and educate others about medicine through Writing. I enjoy producing articles that give readers detailed information about a variety of ailments that can be accessed through the Health Library created by Klarity.

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