Lactobacillus acidophilus | Supplementopedia

Overview

Description: Lactobacillus acidophilus is a Gram-positive, non-spore-forming, rod-shaped bacterium belonging to the lactic-acid-producing (LAB) family.
Natural Habitat: It naturally colonizes the human gastrointestinal and genitourinary tracts.
Use: Widely used as a probiotic to support microbial balance and host health.

Antibiotic-Associated and Travel-Related Diarrhea: Reduces the incidence and duration of antibiotic-associated and travel-related diarrhea (≈30 % risk reduction in meta-analyses).
Lactose Tolerance: Improves lactose tolerance by secreting β-galactosidase, enabling better dairy digestion.
Vaginal Health: Helps maintain vaginal eubiosis, reducing recurrent bacterial vaginosis and yeast infections.
Cholesterol Reduction: Daily supplementation (≥5 × 10⁹ CFU) modestly lowers total-cholesterol and LDL-C (≈5 % reduction) via bile-acid deconjugation.
Immune Modulation: Demonstrated through increased secretory IgA and reduced pro-inflammatory cytokines (IL-6, TNF-α) in both healthy adults and patients with irritable bowel syndrome.
Gut-Brain Axis: Emerging evidence links gut-derived L. acidophilus to the gut-brain axis, with small trials reporting improved mood scores and reduced perceived stress, likely mediated by short-chain-fatty-acid (SCFA) production and vagal signaling.

Lactic Acid Production: Ferments carbohydrates to lactic acid, lowering luminal pH and creating an inhospitable environment for pathogenic microbes (competitive exclusion).
Bacteriocin Production: Produces bacteriocins (e.g., acidophilin) that directly inhibit Gram-negative pathogens.
SCFA and Metabolite Production: Influences entero-endocrine cells, enhancing GLP-1 secretion and improving glucose homeostasis through the production of SCFAs (acetate, propionate) and metabolites such as indole-lactate.
Immune Modulation: The bacterial cell wall’s peptidoglycan and lipoteichoic acid engage Toll-like receptors (TLR-2/6) on intestinal dendritic cells, promoting regulatory T-cell (Treg) differentiation and increasing anti-inflammatory cytokines (IL-10, TGF-β).
Mucosal Barrier Integrity: These immunomodulatory signals enhance mucosal barrier integrity via up-regulation of tight-junction proteins (occludin, claudin-1).
Lactose Hydrolysis: The enzyme β-galactosidase expressed by L. acidophilus hydrolyses lactose, improving tolerance in lactose-intolerant individuals.

General Gut Health: Clinical trials most commonly use 1 × 10⁹–1 × 10¹⁰ colony-forming units (CFU) per day.
Administration: Taken in a single dose with food to protect the bacteria from gastric acid.
Specific Conditions: For antibiotic-associated diarrhea, IBS, or vaginal dysbiosis, higher doses of 2–5 × 10¹⁰ CFU daily for 7–14 days have shown efficacy.
Pediatric Dosage: In pediatric studies, 5 × 10⁸ CFU split into two doses is standard.
Timing: Timing is flexible, though taking the supplement with a meal containing some carbohydrate improves survivability.
Lactose Intolerance: For lactose-intolerant patients, a 10 g dairy-based product containing ≥1 × 10⁹ CFU per serving is recommended.
Immunosuppressed Individuals: Individuals on immunosuppressive therapy may require physician-guided dosing (often ≤5 × 10⁹ CFU) to minimize rare infection risk.

GRAS Status: L. acidophilus is classified as “Generally Recognised As Safe” (GRAS) and is well-tolerated.
Side Effects: Mild, transient gastrointestinal symptoms (bloating, flatulence) may occur during the first 2–3 days of supplementation.
Contraindications: Rare cases of bacteremia or sepsis have been reported in severely immunocompromised patients (e.g., neutropenia, post-transplant) or those with central venous catheters; thus, it is contraindicated in those populations without medical supervision.
Drug Interactions: No clinically relevant drug–probiotic interactions have been documented, though probiotic use may modestly reduce oral-antibiotic efficacy if taken simultaneously; a 2-hour separation is advisable.
Pregnancy and Lactation: Pregnant and lactating women can generally use standard doses, but high-dose regimens (>1 × 10¹¹ CFU) lack robust safety data.

Nature: Lactobacillus acidophilus is a living bacterial cell; it does not have a single molecular formula.
Genome: The organism’s genome averages 1.9–2.0 Mbp, encoding ~1,800–2,000 proteins.
Cell Wall: The cell wall is a thick peptidoglycan layer (type A1γ), comprising N-acetyl-muramic acid linked to L-alanine, D-glutamic acid, L-lysine, and D-alanine residues, cross-linked via peptide bridges.
Surface Components: Surface-associated lipoteichoic acids (LTAs) contain glycerol-phosphate repeats with D-alanine esterification, conferring a net negative charge.
Metabolic Product: The bacteria’s primary metabolic product is L-lactic acid (C₃H₆O₃), a result of homolactic fermentation of glucose via the Embden-Meyerhof pathway.
Enzyme: Enzyme β-galactosidase (EC 3.2.1.23) is a key glycosidase enabling lactose hydrolysis.
Nomenclature: No IUPAC name exists for the organism; the standard taxonomic designation is Lactobacillus acidophilus (formerly Lactobacillus acidophilus).

Origin: Commercial L. acidophilus strains are isolated from human feces, vaginal swabs, or fermented dairy products (yogurt, kefir).
Industrial Production: Industrially, strains are cultured in controlled bioreactors using sterilised milk, whey, or defined carbohydrate media (e.g., glucose, sucrose) under anaerobic, 35–37 °C conditions.
Processing: After growth, cells are harvested, washed, and lyophilised (freeze-drying) with cryoprotectants (trehalose, skim-milk powder) to achieve stable CFU counts.
Quality Control: Quality-focused manufacturers verify strain identity via 16S rRNA sequencing and confirm absence of contaminants (pathogenic bacteria, yeast, endotoxin) through GMP-compliant testing.
Supplement Standards: For supplements, a minimum of 10⁸ CFU per dose is required for label claims in most jurisdictions, and third-party certification (e.g., USP, NSF) is recommended to ensure potency and purity.