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Monday, August 4, 2025

Probiotics


Definition and Scope

Probiotics are defined by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) as:

“Live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.”

They are commonly bacteria (and sometimes yeasts) that naturally reside in the human gastrointestinal (GI) tract, oral cavity, skin, and vagina. Probiotics are administered to restore or enhance the microbiota, improve immunity, maintain mucosal barrier function, and counteract pathogenic organisms. Although available in dietary supplements, fermented foods, and pharmaceutical formulations, probiotics used for medical purposes fall under the drug or therapeutic agent category when indicated for specific clinical conditions.


1. Classification of Probiotics

Probiotics are generally classified based on the genus, species, and strain. Each strain may have unique health effects.

A. Bacterial Probiotics

  1. Lactobacillus species

    • L. acidophilus, L. rhamnosus, L. casei, L. reuteri, L. plantarum

    • Common in the small intestine, vagina, and fermented foods

  2. Bifidobacterium species

    • B. bifidum, B. longum, B. breve, B. infantis

    • Dominant in the colon and in infant gut microbiota

  3. Streptococcus species

    • S. thermophilus (commonly found in yogurt)

  4. Enterococcus species

    • E. faecium, E. faecalis (controversial due to potential pathogenicity)

  5. Escherichia coli Nissle 1917

    • A nonpathogenic strain used therapeutically in ulcerative colitis

  6. Clostridium butyricum

    • A butyrate-producing anaerobe beneficial for gut health

B. Yeast Probiotics

  1. Saccharomyces boulardii

    • A non-pathogenic yeast used extensively in diarrheal conditions

2. Mechanisms of Action

Probiotic activity is strain-specific, but the following mechanisms are commonly observed:

A. Modulation of Gut Microbiota

  • Restoration of microbial balance (eubiosis) by inhibiting pathogen overgrowth (e.g., Clostridioides difficile)

B. Immune System Regulation

  • Enhancement of mucosal immunity via stimulation of secretory IgA

  • Modulation of T-regulatory cells, balancing pro- and anti-inflammatory cytokines

C. Barrier Function Improvement

  • Upregulation of tight junction proteins (e.g., occludins, claudins) to maintain intestinal epithelial integrity

D. Antimicrobial Production

  • Secretion of bacteriocins, organic acids (lactic acid, acetic acid), and hydrogen peroxide that inhibit pathogens

E. Competitive Exclusion

  • Occupation of binding sites and competition for nutrients to prevent pathogen adherence

F. Enzymatic Activity

  • Production of lactase and bile salt hydrolase; beneficial in lactose intolerance and cholesterol metabolism

G. Metabolite Production

  • Generation of short-chain fatty acids (SCFAs) like butyrate which fuel colonocytes and reduce inflammation

3. Clinical Applications

Probiotics have been investigated in a wide range of gastrointestinal, metabolic, allergic, infectious, and neurological disorders. Below are evidence-based indications:

A. Gastrointestinal Disorders

  • Antibiotic-associated diarrhea (AAD): L. rhamnosus GG, S. boulardii

  • Clostridioides difficile infection (CDI): S. boulardii adjunct therapy

  • Irritable bowel syndrome (IBS): B. infantis, L. plantarum reduce bloating and pain

  • Ulcerative colitis: E. coli Nissle 1917, VSL#3

  • Pouchitis: Multistrain probiotics (e.g., VSL#3)

  • Functional constipation: B. lactis, L. casei Shirota

B. Infections

  • Traveler’s diarrhea: S. boulardii

  • H. pylori eradication adjunct: Lactobacillus spp. reduce side effects and improve eradication rates

  • Bacterial vaginosis and candidiasis: Vaginal or oral L. rhamnosus and L. reuteri

C. Allergic and Atopic Conditions

  • Atopic dermatitis in children: L. rhamnosus GG

  • Asthma and allergic rhinitis (under investigation)

D. Neonatal and Pediatric Uses

  • Necrotizing enterocolitis (NEC) prevention: B. infantis, L. rhamnosus (in preterm neonates)

  • Infant colic: L. reuteri DSM 17938

E. Immune Support

  • General use in reducing upper respiratory infections (URIs), especially in children and athletes

F. Mental Health (Psychobiotics)

  • L. helveticus and B. longum shown to reduce anxiety and depression symptoms via gut-brain axis

G. Metabolic Syndrome and Obesity

  • L. gasseri, B. breve, and others under investigation for reducing insulin resistance and visceral fat

4. Pharmaceutical Formulations and Routes

Probiotics are available in various formulations:

  • Oral capsules and tablets: Most common delivery method

  • Powders and sachets: May contain higher CFU (colony-forming units)

  • Chewables and lozenges: Especially for oral/vaginal health

  • Vaginal capsules/suppositories: For localized infections

  • Enteric-coated forms: Protect from gastric acid degradation

  • Probiotic-enriched foods: Yogurt, kefir, kimchi, sauerkraut

5. Pharmacokinetics

Probiotics are not absorbed systemically. Their effect is local within the GI or urogenital tract.

  • Survivability: Acid and bile resistance is strain-dependent

  • Colonization: Temporary; most strains do not permanently colonize the host

  • Excretion: Exit via feces within days to weeks after discontinuation

Note: Factors like antibiotic use, pH levels, and gut motility affect colonization and efficacy.

6. Examples of Generic Probiotic Strains

GenusSpecies/StrainExample Use
LactobacillusL. rhamnosus GGDiarrhea, eczema
LactobacillusL. reuteri DSM 17938Infant colic, dental health
BifidobacteriumB. infantis 35624IBS, colitis
BifidobacteriumB. lactis BB-12Immunity, constipation
SaccharomycesS. boulardii CNCM I-745AAD, C. difficile, traveler’s diarrhea
Escherichia coliE. coli Nissle 1917Ulcerative colitis
Mixed strainsVSL#3 (8-strain formulation)IBD, pouchitis



7. Safety and Adverse Effects

Probiotics are generally regarded as safe (GRAS) in healthy individuals. However, rare adverse effects may occur in specific populations.

Common side effects:

  • Bloating and flatulence

  • Abdominal discomfort during initial administration

Serious (but rare) adverse events:

  • Bacteremia or fungemia in immunocompromised or critically ill patients (e.g., S. boulardii fungemia)

  • Sepsis in neonates or patients with central lines

  • Endocarditis in patients with structural heart defects (rare)

Risk factors for complications:

  • Immunosuppression

  • Central venous catheters

  • Prematurity

  • Intestinal mucosal injury

8. Contraindications

Probiotics should be avoided or used with caution in the following situations:

  • Severely immunocompromised patients (e.g., chemotherapy, HIV/AIDS)

  • Critically ill or ICU patients

  • Neonates with very low birth weight (<1000 g) unless under specialist care

  • Patients with short bowel syndrome or central venous access

  • Known hypersensitivity to any formulation excipient

9. Precautions

  • Storage: Refrigeration required for some formulations; shelf stability varies

  • Viability: Ensure product has clearly labeled CFU count and strain identification

  • Antibiotic timing: Administer probiotics 2–3 hours apart from antibiotics to preserve efficacy

  • Duration: Longer-term use may be required for chronic conditions (e.g., IBS, IBD)

  • Professional consultation: Necessary before initiating probiotics in vulnerable populations

10. Drug Interactions

Probiotics are biological agents, not classical drugs, but several interactions should be noted:

A. Antibiotics

  • May reduce viability of bacteria-based probiotics

  • Use S. boulardii (yeast) if co-administering with antibiotics

  • Separate administration by 2–3 hours

B. Immunosuppressants

  • Increased risk of systemic infection from live organisms

C. Antifungals (e.g., fluconazole)

  • Inactivate S. boulardii if taken concurrently

D. Proton Pump Inhibitors (PPIs)

  • May enhance probiotic survival due to decreased gastric acidity

11. Regulatory Considerations

A. In the U.S.

  • Most probiotics are marketed as dietary supplements, not drugs

  • Not subject to the same FDA drug approval standards unless labeled for a specific therapeutic use

B. In Europe

  • European Food Safety Authority (EFSA) strictly regulates health claims

  • Some strains have Qualified Presumption of Safety (QPS) status

C. WHO/FAO Guidelines

  • Recommend safety evaluation for each strain before human use

12. Examples of Probiotic Formulations

  • Florastor®: S. boulardii CNCM I-745

  • Culturelle®: L. rhamnosus GG

  • Align®: B. infantis 35624

  • VSL#3®: Combination of 8 bacterial strains

  • Mutaflor®: E. coli Nissle 1917



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