Bifidobacterium longum

Overview

• Bifidobacterium longum is a Gram‑positive, anaerobic, rod‑shaped bacterium.
• It naturally colonizes the human gastrointestinal tract, especially the colon and distal ileum.
• It is primarily used as a probiotic to support a balanced gut microbiota.
• It contributes to digestive health and systemic immune modulation.

Benefits

• Gastrointestinal Symptoms: Improves symptoms like constipation, bloating, and diarrhea by enhancing barrier integrity and competing with pathogenic microbes.
• Immune Modulation: Modulates immune responses, reducing the incidence of respiratory infections and mild allergic reactions through increased secretory IgA and regulatory T‑cell activity.
• Metabolic Regulation: Attenuates metabolic dys‑regulation, modestly lowering fasting glucose and triglycerides in overweight adults via short‑chain-fatty-acid (SCFA) production.
• Neuro-cognitive Health: Supports neuro‑cognitive health by influencing the gut‑brain axis, with pilot studies showing reduced anxiety scores and improved memory recall in healthy adults.
• Antibiotic-Associated Dysbiosis: Aids in the prevention of antibiotic‑associated dysbiosis, shortening the duration of diarrhea after broad-spectrum antibiotic courses.
• All benefits are dose‑dependent and most robust when the strain is clinically validated (e.g., B. longum BB536, 171/2).

How It Works

• Colonization and Fermentation: B. longum colonizes the colon where it ferments complex carbohydrates (e.g., oligosaccharides, resistant starch).
• SCFA Production: Produces acetate, lactate, and other SCFAs that lower luminal pH, inhibiting pathogenic growth.
• Intestinal Barrier Enhancement: Reinforces tight‑junction proteins (occludin, claudin‑1) via the MAPK and NF‑κB pathways, reducing intestinal permeability.
• Immune Modulation via PSA: The bacterium’s surface‑attached polysaccharide A (PSA) interacts with dendritic cells, promoting IL‑10–producing regulatory T cells and dampening pro‑inflammatory cytokines (TNF‑α, IL‑6).
• Gut-Brain Axis Influence: Production of GABA and tryptophan metabolites influences the vagus nerve and serotonergic pathways, linking gut alterations to brain function.
• Bile Acid Modulation: B. longum’s ability to deconjugate bile acids modulates lipid metabolism and bile‑acid signaling (FXR, TGR5), contributing to metabolic effects.

Dosage

• General Gut Health: Most human studies use 1 × 10⁹–1 × 10¹¹ colony‑forming units (CFU) per day, with 1–5 × 10⁹ CFU being the most common dose.
• Therapeutic Aims: For therapeutic aims (e.g., IBS, antibiotic‑associated diarrhea), 5–10 × 10⁹ CFU daily for 4–12 weeks is typical.
• Administration: Capsules or sachets taken with food (especially a carbohydrate‑rich meal) improve survival through gastric acid.
• Infant Dosage: For infants, 1–5 × 10⁸ CFU (age‑appropriate formulation) is recommended.
• Higher Doses: Higher doses (≥1 × 10¹⁰ CFU) have been used in clinical trials for metabolic or neuro‑cognitive outcomes.
• Timing: Timing can be flexible, though consistent daily intake yields the most stable colonization.
• Special Populations: Pregnant or lactating women should follow manufacturer‑specific guidance; pediatric dosing should be weight‑adjusted.

Safety & Side Effects

• General Safety: B. longum is Generally Recognized As Safe (GRAS).
• Side Effects: Low incidence of mild gastrointestinal events (flatulence, mild bloating) that typically resolve within a few days.
• Immunocompromised Patients: Immunocompromised patients (e.g., undergoing chemotherapy, organ transplantation) are advised to avoid high‑dose probiotic use due to rare reports of bacteremia or sepsis.
• Drug Interactions: No significant drug‑interaction data exist, but caution is advised when combined with broad-spectrum antibiotics, which may reduce viability.
• Contraindications: Contraindicated in individuals with severe central‑line infections or uncontrolled critical illness.
• Pregnancy and Lactation: Pregnant and lactating women may use standard doses, but clinicians should assess individual risk.
• Monitoring: Monitoring for fever or systemic infection is prudent in high‑risk populations.

Chemistry

• Living Organism: B. longum is a living organism; therefore, it does not have a single molecular formula.
• Cellular Structure: Its cellular structure includes a thick peptidoglycan layer (Gram‑positive), teichoic acids, and surface‑attached polysaccharide A (PSA) with repeating N‑acetyl‑glucosamine and N‑acetyl‑muramic acid units.
• Genome: Genomic analyses reveal a 2.5–2.9 Mbp genome encoding ~2,000–2,500 proteins, with a GC content of ~60 mol %.
• Metabolic Products: The bacterium’s metabolic products—acetate (C₂H₃O₂⁻), lactate (C₃H₅O₃⁻), and SCFAs—have defined chemical formulas (e.g., acetate: C₂H₃O₂⁻).
• PSA: The primary active component, PSA, is a high‑molecular‑weight polysaccharide (≈10⁶ Da) composed of β‑(1→6)‑linked N‑acetyl‑glucosamine residues, which is responsible for many immunomodulatory effects.

Sources & Quality

• Isolation: Commercial B. longum strains are typically isolated from human feces, breast‑milk, or infant gut samples under anaerobic conditions.
• Culture: Strains are then cultured in reinforced clostridial media, harvested, and lyophilized or freeze‑dried with protective cryoprotectants (e.g., maltodextrin).
• Quality Control: High‑quality supplements employ GMP‑certified fermentation, followed by rigorous strain identification via 16S rRNA sequencing and whole‑genome sequencing to confirm strain identity (e.g., BB536, 171/2).
• Viability: The final product must meet viability criteria (≥10⁹ CFU per dose) and be tested for contaminants (pathogenic bacteria, yeast, endotoxin).
• Storage: Quality considerations include storage temperature (≤ 4 °C for liquid formulations, ≤ 25 °C for capsules) and shelf‑life testing to ensure stable colony counts throughout the product’s expiry.