Lactobacillus casei

Overview

• Lactobacillus casei is a Gram-positive, facultatively anaerobic, rod-shaped bacterium belonging to the Lactobacillus genus (now often classified within the Lactobacillus paracasei clade).
• It is a natural inhabitant of the human gastrointestinal tract.
• It is widely used as a probiotic to modulate gut microbiota, enhance barrier function, and support immune homeostasis.

Benefits

• Digestive Health: Improves digestive health by reducing the incidence of antibiotic-associated diarrhea and shortening the duration of infectious gastroenteritis.
• Immune Modulation: Modulates immune responses, lowering the risk of respiratory infections and attenuating allergic inflammation.
• Metabolic Health: Supports metabolic health, modestly improving fasting glucose and lipid profiles in overweight adults.
• Intestinal Barrier Integrity: Enhances intestinal barrier integrity, reducing systemic endotoxin levels.
• H. pylori Eradication: Assists in the eradication of Helicobacter pylori when combined with standard therapy.
• Gut-Brain Axis: Influences the gut–brain axis, with pilot trials indicating reduced anxiety scores and improved cognitive performance in older adults.
• All benefits are supported by randomized controlled trials (RCTs) and meta-analyses published between 2015–2024.

How It Works

• Colonization: Exerts its effects primarily through colonization of the distal small intestine and colon.
• Metabolite Production: Produces lactic acid, bacteriocins (e.g., caseicin), and short-chain fatty acids (SCFAs) such as acetate and butyrate (via cross-feeding).
• pH and Pathogen Inhibition: These metabolites lower luminal pH, inhibit pathogenic bacteria, and activate G-protein-coupled receptors (GPR41/43) on enteroendocrine cells, stimulating GLP-1 secretion and improving insulin sensitivity.
• Immune Interaction: Interacts with dendritic cells via Toll-like receptor 2 (TLR2) and induces regulatory T-cell (Treg) differentiation through IL-10 production, thereby dampening pro-inflammatory cytokine cascades (NF-κB, MAPK).
• Tryptophan Pathway: Influences the tryptophan–kynurenine pathway, affecting serotonin synthesis and potentially contributing to its observed neuro-behavioral effects.

Dosage

• Typical Dosage: Commercial probiotic products typically provide 1 × 10⁸ to 1 × 10¹⁰ colony-forming units (CFU) per serving.
• General Gut Health: For general gut health, 1 × 10⁹ CFU daily for 4–8 weeks is common.
• Higher Doses: Higher doses (≥5 × 10⁹ CFU) are used in clinical trials targeting antibiotic-associated diarrhea or H. pylori eradication.
• Timing: The optimal timing is on an empty stomach (30 min before a meal) to maximize gastric survival, though some studies show comparable efficacy when taken with food.
• Athletes: In athletes, a 2 × 10⁹ CFU dose taken twice daily has been used to modulate exercise-induced immune suppression.
• Adjustments: Adjustments may be needed for children (0.5–1 × 10⁹ CFU) and immunocompromised patients (lower, 1 × 10⁸ CFU) under medical supervision.

Safety & Side Effects

• GRAS Status: L. casei is Generally Recognized as Safe (GRAS) and well tolerated.
• Side Effects: Mild gastrointestinal symptoms (bloating, gas) may occur during initial colonization.
• Rare Complications: Rarely, bacteremia or sepsis has been reported in severely immunocompromised patients (e.g., neutropenia, organ transplantation).
• Contraindications: Contraindications include patients with central venous catheters, severe pancreatitis, or those receiving high-dose immunosuppressants without physician oversight.
• Drug Interactions: No clinically significant drug–probiotic interactions have been documented, but concurrent use with antibiotics may reduce viability; spacing the dose by ≥2 h is recommended.
• Pregnancy/Lactation: Pregnant and lactating women may safely use standard doses, though data remain limited; consultation with a healthcare provider is advised.

Chemistry

• Microorganism: Lactobacillus casei is a living microorganism rather than a single chemical entity; thus, a molecular formula does not apply.
• Cell Structure: The bacterium is a Gram-positive, non-spore-forming rod (0.5 × 2–5 µm) with a thick peptidoglycan cell wall containing teichoic acids and a cytoplasmic membrane rich in phospholipids (phosphatidylglycerol, cardiolipin).
• Genome: Its genome is ~2.9 Mbp, encoding ~2,800 protein-coding genes, including the lac operon for lactic acid fermentation (homo-lactic pathway).
• Key Metabolites: Key metabolites include L-lactate (C₃H₆O₃, IUPAC: 2-hydroxypropanoic acid) and bacteriocins (e.g., caseicin, a peptide with a defined amino-acid sequence).
• Surface Proteins: The bacterium’s surface proteins (e.g., mucus-binding protein, MUB) facilitate adhesion to intestinal epithelium.

Sources & Quality

• Natural Sources: L. casei is isolated from traditional fermented foods (e.g., dairy, sauerkraut, kimchi) and human fecal samples.
• Industrial Production: Industrially, strains are cultivated in sterile, anaerobic bioreactors using de-proteinized whey or soy-based media, ensuring high CFU yields.
• Strain Selection: Strain selection (e.g., ATCC 393, DSM 20011) follows strict taxonomic verification (16S rRNA sequencing).
• Processing: Post-culture, cells are harvested, lyophilized with protective cryoprotectants (e.g., trehalose) and encapsulated to preserve viability.
• Quality Control: Quality criteria include ≥10⁹ CFU per dose at expiration, absence of contaminants (E. coli, Salmonella), and stability under 25 °C for ≥12 months.
• Third-Party Testing: Third-party testing (e.g., USP, NSF) ensures strain identity and potency, which are critical for reproducible clinical outcomes.