Probiotics

The main genera and strains

The most studied genera used in the formulation of dietary supplements are Lactobacillus, Bifidobacterium, and the yeast Saccharomyces. Each genus includes numerous species, and each species includes distinct strains-each with its own functional characteristics.

The Lactobacillus species most commonly found in probiotic products include L. acidophilus, L. rhamnosus, L. casei, L. reuteri, L. fermentum and L. plantarum. The genus Bifidobacterium includes B. longum, B. bifidum, B. breve and B. infantis among the most studied species. The yeast Saccharomyces cerevisiae var. boulardii occupies a special position: it is a eukaryotic microorganism, not a bacterium, with antibiotic resistance characteristics that make it useful in specific contexts.

A key principle to keep in mind is strain specificity: properties documented for one strain are not automatically transferable to other strains of the same species. Any claims about the properties of a probiotic always refer to the specific strain on which the research was conducted.

The challenge of survival: from the stomach to the gut

To exert their effect, probiotic microorganisms must reach the intestine alive and in sufficient numbers. The path is not without obstacles: gastric acidity and bile salts in the duodenum are the main barriers that select which strains make it to their destination intact.

Survival depends on multiple factors: the intrinsic nature of the strain, product formulation, the matrix in which the probiotic is incorporated, and storage conditions. Microencapsulation technologies and protected release systems are now established tools to improve strain resistance to gastric transit and ensure adequate viable counts at the time of intake.

The Italian Ministry of Health Guidelines set 1 billion live cells (10⁹ CFU) per dose as the minimum guideline threshold for supplement products. The count must be guaranteed until the expiration date of the product, not at the time of manufacture.

Mechanism of action

Probiotics act through multiple mechanisms that take place at the level of the intestinal mucosa and the gut-associated immune system (GALT). The main ones are:

• Ecological competition — probiotic strains compete with potentially harmful microorganisms for available nutrients and adhesion sites to the intestinal mucosa, limiting their proliferation.
• Production of antimicrobial substances — some strains produce lactic acid, acetic acid, bacteriocins, and other compounds that help maintain an unfavorable environment for pathogens.
• Production of Short Chain Fatty Acids (SCFA) — specifically butyrate, propionate, and acetate, which play a trophic role for colonic epithelial cells and participate in the regulation of the local inflammatory response.
• Modulation of intestinal immune response — Probiotics interact with mucosal immune system cells, influencing the balance between pro-inflammatory response and immunological tolerance.
• Support intestinal barrier function — some strains promote maintenance of the integrity of tight junctions (tight junctions) between epithelial cells, helping to reduce intestinal permeability.

Gut Microbiota and Probiotics

Probiotics fit into the complex ecology of the Gut Microbiota — the set of microorganisms that inhabit the human digestive tract. A balanced Microbiota in eubiotic condition is associated with the proper functioning of numerous physiological processes: from digestion and nutrient absorption to immune system regulation and the gut-brain axis.

Probiotics do not replace the resident Microbiota, nor do they permanently alter it. Rather, they act as temporary modulators: their presence promotes more favorable conditions for the beneficial bacterial populations already present. For this reason, association with Prebiotics-the selectively fermented fibers that act as substrates for beneficial microorganisms — is often considered more effective than probiotic supplementation alone.

Prebiotics and Postbiotics: the context of the biotic family

Probiotics are part of a larger system that includes Prebiotics and Postbiotics. Prebiotics are non-digestible substrates — primarily fiber and oligosaccharides — that selectively nourish the beneficial microorganisms already in the gut. Postbiotics are the bioactive compounds produced by microorganisms as a result of their metabolism: short-chain fatty acids, peptides, enzymes, and B vitamins.

The distinction is relevant in formulation: products that combine Probiotics and Prebiotics are called Symbiotics. This combination aims to optimize both the survival of the probiotic strain during intestinal transit and its metabolic activity once it reaches the colon.

The forms available for formulation

Probiotics can be formulated in different galenzyme forms, each with specific implications for product stability and consumer compliance:

• Vegetable Capsules (HPMC) — the most common form. Capsules protect contents from moisture and oxygen. The hydroxypropyl methyl cellulose version is compatible with vegan formulations.
• Sachets and Stick Packs — suitable for powder or granulated formulations. They allow high doses and good shelf life when packaged with appropriate barrier materials. Strongly growing format in the on-the-go segment.
• Chewable Tablets and Gummies — format with high acceptability, particularly for children and consumers who prefer to avoid Capsules. Require attention to strain stability during production and storage.
• Liquids and Ampoules — allow formulation in an aqueous matrix, often with the addition of prebiotics and vitamins. They require special precautions to maintain microbial viability.
• Freeze-dried formulations — freeze-drying is the most widely used stabilization method for probiotic strains. It prolongs shelf life by drastically reducing water activity, maintaining cell viability until rehydration.

The regulatory framework in Italy

In Italy, Probiotics in food supplements are regulated by the Ministry of Health Guidelines on Probiotics and Prebiotics (revised March 2018), which define their identification, safety and activity requirements. The functional claim allowed on the label is: «promotes the balance of intestinal flora».

At the European level, EFSA has not to date approved specific health claims for Probiotics as a category under EC Regulation 1924/2006. This does not reflect a negative judgment on the safety or usefulness of Probiotics, but the difficulty of attributing generic effects to categories of microorganisms whose behaviors are inherently strain-specific. Scientific research in the field is extensive and constantly evolving.

The health of the Gut Microbiota is a rapidly developing field of research. The information in this fact sheet is for informational purposes only and is not a substitute for the advice of a health care professional. You should consult your physician or pharmacist before beginning any supplementation with Probiotics, particularly in the presence of chronic diseases, ongoing therapies, or immunodepressed conditions.