Streptococcus thermophilus

Overview

• Streptococcus thermophilus is a Gram-positive, facultatively anaerobic, non-spore-forming cocci.
• It thrives at temperatures of 42–45 °C.
• It is widely recognized as a starter culture in dairy fermentation (yogurt, cheese).
• It produces lactic acid, contributes to texture, extends shelf-life, and delivers live probiotic cells.

Benefits

• Gut Health: Supports gut health by enhancing lactose digestion and maintaining a balanced microbiota.
• Symptom Reduction: Can reduce functional gastrointestinal symptoms (e.g., bloating, constipation).
• Lactose Tolerance: In lactose-intolerant adults, daily ingestion of 10⁸–10⁹ CFU has been shown to increase lactose tolerance by 30–40 % (Baker et al., 2020).
• Immune Modulation: Modulates immune responses (increased secretory IgA, reduced pro-inflammatory cytokines).
• Lipid Profiles: Has modest effects on blood lipid profiles, with meta-analyses reporting modest reductions in total cholesterol (≈5 %) when combined with other lactic acid bacteria.
• Oral Health: Preliminary data suggest a modest benefit for oral-cavity health by reducing cariogenic Streptococcus mutans counts.

How It Works

• Metabolic Activity: Exerts its effects primarily via its metabolic activity in the gut lumen.
• Lactose Hydrolysis: High β-galactosidase activity hydrolyzes lactose into glucose and galactose, facilitating absorption in lactose-intolerant individuals.
• SCFA Production: Ferments carbohydrates to produce lactic acid, acetate, and other SCFAs (particularly acetate and propionate) that lower colonic pH, inhibiting pathogenic bacteria and promoting growth of beneficial Bifidobacterium spp.
• Immune Activation: Surface-associated peptidoglycan and teichoic acids interact with pattern-recognition receptors (TLR2/6) on intestinal epithelial cells, activating the MyD88-dependent pathway that up-regulates tight-junction proteins (e.g., claudin-1, occludin) and enhances barrier function.
• Prebiotic Effects: Secreted exopolysaccharides (EPS) act as pre-biotic substrates, fostering a symbiotic environment that supports immunomodulation (increased IL-10, decreased TNF-α) and systemic metabolic effects.

Dosage

• Typical Dosage: Clinical studies commonly employ 10⁸–10¹⁰ CFU per day of live S. thermophilus (often as part of a multi-strain probiotic).
• Lactose Intolerance/Gut Health: For lactose-intolerance or general gut health, 1 × 10⁹ CFU taken with a meal containing lactose is typical, taken once daily.
• Immune/Lipid Effects: For immune-modulatory or lipid-modifying effects, 5 × 10⁹ CFU taken with breakfast for 4–8 weeks has been used.
• Combination Therapy: When combined with Lactobacillus spp., a total dose of 1–2 × 10¹⁰ CFU per day is common.
• Timing: Timing may be flexible, but ingestion with food improves survival through gastric acidity.
• Pediatric Dosage: In pediatric formulations, 5 × 10⁸ CFU per day is considered safe.
• Therapeutic Studies: For therapeutic studies (e.g., ulcerative colitis), higher doses up to 5 × 10¹⁰ CFU have been administered under medical supervision.

Safety & Side Effects

• GRAS Status: Streptococcus thermophilus is Generally Recognized As Safe (GRAS).
• Side Effects: Mild, transient gastrointestinal symptoms (bloating, gas) may occur when initiating supplementation.
• Risk in Immunocompromised: Rare cases of bacteremia or sepsis have been reported in severely immunocompromised patients (e.g., neutropenic oncology patients) receiving high-dose probiotic therapy; thus, such individuals should avoid high-dose supplements.
• Drug Interactions: No significant drug–probiotic interactions have been documented, but caution is advised with antibiotics that may reduce viability (e.g., broad-spectrum β-lactams).
• Pregnancy/Lactation: Pregnant or lactating women can use standard doses (≤10⁹ CFU/day) without adverse events.
• Dairy Allergy: Individuals with severe dairy allergy should verify that the product is free of residual milk proteins.

Chemistry

• Microorganism: Streptococcus thermophilus is a living microorganism; therefore, it does not have a single molecular formula.
• Genome: Its genome is a circular chromosome of ~1.9 Mbp, encoding ~1,800 proteins.
• Cell Wall: The cell wall is composed of a thick peptidoglycan layer (N-acetylmuramic acid–N-acetylglucosamine polymer cross-linked by L-lysine–D-alanine bridges) with teichoic acids (ribitol-phosphate polymers) that confer the characteristic Gram-positive staining.
• Surface Proteins: Major surface proteins include the M protein-like adhesins (e.g., SrtA-anchored proteins) and exopolysaccharide (EPS) biosynthetic enzymes (e.g., glycosyltransferases).
• Metabolic Pathways: The bacterium’s metabolic pathways include glycolysis, the pentose-phosphate pathway, and the L-lactate dehydrogenase–mediated conversion of pyruvate to L-lactate (ΔG ≈ −25 kJ mol⁻¹).
• EPS Production: The EPS produced are high-molecular-weight polysaccharides (≈10⁶ Da) composed mainly of glucose, galactose, and N-acetylglucosamine.

Sources & Quality

• Natural Source: Streptococcus thermophilus is isolated from traditional dairy fermentations (e.g., yogurt, cheese) where it naturally dominates at thermophilic temperatures.
• Commercial Production: Commercial production utilizes controlled fermentation of sterile milk or whey media in bioreactors at 42–45 °C, yielding high-density cultures (≥10¹⁰ CFU mL⁻¹).
• Strain Selection: Strains are selected for robust β-galactosidase activity, acid tolerance, and stable exopolysaccharide production.
• Processing: After fermentation, cells are harvested, lyophilized, and encapsulated (e.g., double-layer microencapsulation) to protect viability.
• Quality Control: Quality control includes strain identification by 16S rRNA sequencing, absence of pathogenic genes (e.g., cagA, vir), and CFU verification per label claim.
• Manufacturing Standards: Good Manufacturing Practice (GMP) and third-party testing (e.g., USP, NSF) are essential to ensure purity, potency, and absence of contaminants (e.g., E. coli, Salmonella).