Lactobacillus rhamnosus | Supplementopedia

Overview

Lactobacillus rhamnosus is a Gram-positive, non-spore-forming, rod-shaped bacterium belonging to the lactic-acid-producing Lactobacillus genus.
It is a well-studied probiotic strain (most commonly the GG/ATCC 53103 isolate).
When ingested in sufficient numbers, it can survive gastric transit, temporarily colonize the intestinal mucosa, and modulate host physiology for health-promoting effects.

Gastro-intestinal health: L. rhamnosus reduces the incidence and duration of acute infectious diarrhea in children (≈ 1 log CFU reduction) and shortens antibiotic-associated diarrhea (≈ 50 % reduction).
Vaginal & urinary health: Clinical trials demonstrate a 30–40 % reduction in recurrent bacterial vaginosis and urinary-tract infection recurrence when taken 2–3 × 10⁹ CFU daily.
Immune modulation: Meta-analyses report decreased incidence of upper-respiratory infections (RR 0.79) and reduced severity of atopic dermatitis in infants (OR 0.55).
Mental-cognitive: Randomized trials report modest improvements in anxiety scores (HADS-A ↓ 1.5 points) and stress-related cortisol in healthy adults, likely via gut-brain axis signaling.
Metabolic: Small-scale studies show modest reductions in fasting glucose (≈ 5 mg/dL) and LDL-cholesterol (≈ 5 mg/dL) after 8 weeks of ≥10⁹ CFU/day in overweight adults.

L. rhamnosus adheres to intestinal epithelial cells via surface proteins (e.g., SpaC) and produces lactic acid, lowering luminal pH and inhibiting pathogenic growth.
It secretes bacteriocins (e.g., lactobacillin) that directly suppress pathogens.
The strain activates Toll-like receptor 2 (TLR-2) and NOD2 pathways, leading to regulated NF-κB signaling and increased production of anti-inflammatory cytokines (IL-10, TGF-β) while suppressing pro-inflammatory cytokines (IL-6, TNF-α).
It also stimulates dendritic-cell maturation, enhancing regulatory T-cell (Treg) populations.
Metabolically, L. rhamnosus ferments carbohydrates to short-chain fatty acids (acetate, lactate) that serve as energy for colonocytes and act as ligands for G-protein-coupled receptors (GPR43/41), influencing gut-brain signaling and glucose homeostasis.
The strain also modulates the hypothalamic-pituitary-adrenal axis, reducing cortisol secretion through vagal afferent signaling.

General health / maintenance: 1–10 × 10⁹ CFU per day (single or divided dose).
Acute diarrhea or antibiotic-associated dysbiosis: 10–20 × 10⁹ CFU daily for 5–10 days, started at the first sign of symptoms.
Vaginal/UTI prophylaxis: 5–10 × 10⁹ CFU daily for 2–3 months, then as needed.
Infants & children: 1–5 × 10⁸ CFU daily (age-adjusted) for prevention of atopic dermatitis or rotavirus-related diarrhea.
Timing: Take with a meal containing some fat to enhance survival through the stomach; consistency is more important than exact timing.
Special cases: Higher doses (≥10¹⁰ CFU) have been studied in irritable bowel syndrome and may be used under clinician supervision.

L. rhamnosus is Generally Recognized As Safe (GRAS) for healthy adults.
Mild, self-limiting gastrointestinal symptoms (bloating, flatulence) occur in <5 % of users.
Rare cases of bacteremia or endocarditis have been reported in severely immunocompromised patients (e.g., those with neutropenia, central venous catheters, or severe acute pancreatitis).
Contraindications: individuals with compromised immune systems, patients undergoing hematopoietic stem-cell transplantation, or those receiving high-dose antibiotics without concurrent probiotic safety data.
No clinically relevant drug-interaction data exist, but co-administration with antibiotics may reduce viable CFU; a 30-minute separation is advised.
Pregnant and lactating women may use standard doses (≤10 × 10⁹ CFU) safely, but high-dose regimens should be discussed with a healthcare provider.

Lactobacillus rhamnosus is a living microorganism, not a single chemical entity.
Its cell envelope comprises a thick peptidoglycan layer (Gram-positive) linked to teichoic acids (e.g., wall-teichoic acid with D-alanine residues) and a cytoplasmic membrane rich in phospholipids (phosphatidylglycerol, cardiolipin).
The genome of the reference GG strain is ~2.99 Mbp, encoding ~2,900 proteins, with a GC content of ~46 %.
The major metabolic product is L-lactic acid (C₃H₆O₃, IUPAC: (S)-lactate), generated via homolactic fermentation of carbohydrates via the Embden–Meyerhof pathway.
The bacterium also synthesizes exopolysaccharides (EPS) composed of glucose, galactose, and rhamnose units, contributing to biofilm formation and immune modulation.

Commercially, L. rhamnosus is cultivated from the well-characterized GG/ATCC 53103 strain, isolated originally from a healthy human gastrointestinal tract in 1983.
Production involves anaerobic fermentation in dairy-based media (e.g., skim-milk or soy-based broth) under controlled pH (≈ 5.5) and temperature (≈ 37 °C) to achieve high viable counts.
After fermentation, cells are harvested, washed, and lyophilized with cryoprotectants (e.g., trehalose) to maintain viability.
Quality control includes strain verification by 16S-rRNA sequencing, CFU enumeration, and absence of contaminants (e.g., E. coli, Staphylococcus spp.).
Good Manufacturing Practices (GMP) and third-party testing (e.g., USP, NSF) ensure purity, potency, and stability.
Natural sources include fermented dairy (yogurt, kefir), fermented vegetables, and some probiotic-enriched foods, though supplement formulations provide standardized, high-dose CFU counts that are difficult to achieve via diet alone.