Streptococcus thermophilus is a thermophilic bacterium commonly used in the production of yogurt and cheeses. This bacterium helps ferment lactose, the sugar in milk, turning it into lactic acid. This contributes to the coagulation of milk and the development of the characteristic texture and flavor of these dairy products. 

The name describes the structure of the molecule:

• Streptococcus is a genus of coccus-shaped bacteria that are mostly found in chains. They are known for causing a variety of infections, but many strains are also part of the normal flora of the human body or are used in industrial processes.
• thermophilus comes from Greek and means "heat lover". This term refers to this bacterium's ability to grow and thrive at relatively high temperatures, a useful trait in many food fermentation processes.

Industrial Production Process

• Strain selection. The process begins with the selection of a pure strain of Streptococcus thermophilus that exhibits desired characteristics for specific applications.
• Culture medium preparation. A specific culture medium is prepared, enriched with essential nutrients such as peptones, yeast extracts, and glucose, which support optimal bacterial growth.
• Fermentation. The strain is inoculated into sterile fermenters where fermentation takes place under controlled conditions of temperature (typically between 42°C and 45°C), pH, and anaerobiosis.
• Monitoring and control. During fermentation, bacterial growth is constantly monitored to ensure optimal development and prevent contamination.
• Bacteria harvesting. Once fermentation is complete and the desired cell count is achieved, the bacteria are harvested via centrifugation.
• Lyophilization or freezing. The bacteria can be lyophilized or frozen to preserve stability and facilitate transport and storage.
• Formulation. The final product can be formulated as a dry or frozen starter culture, ready to be used in the production of dairy products.
• Quality control. Each batch produced undergoes rigorous quality control to verify vitality, purity, and effectiveness in lactic fermentation.

What it is used for and where

Cosmetics - INCI Functions

• Humectant. Hygroscopic compound used to minimise water loss in the skin and to prevent it from drying out by facilitating faster and greater absorption of water into the stratum corneum of the epidermis.  The epidermis is the most superficial of the three layers that make up human skin (epidermis, dermis and hypodermis) and is the layer that maintains hydration in all three layers. In turn, the epidermis is composed of five layers: horny, the most superficial, granular, spinous, shiny, and basal. Humectants have the ability to retain the water they attract from the air in the stratum corneum and have the function of moisturising the skin. They are best used before emollients, which are oil-based.
• Skin conditioning agent. It is the mainstay of topical skin treatment as it has the function of restoring, increasing or improving skin tolerance to external factors, including melanocyte tolerance. The most important function of the conditioning agent is to prevent skin dehydration, but the subject is rather complex and involves emollients and humectants that can be added in the formulation.

 Here are some of the main uses and benefits of Streptococcus thermophilus.

Yogurt and Cheese Production. This bacterium is essential in the milk fermentation process, contributing to the production of yogurt and cheeses (1) such as mozzarella and pecorino.

Digestive Health. It helps stabilize the intestinal flora and can contribute to reducing symptoms of disorders such as lactose intolerance, aiding in the digestion of milk in sensitive individuals (2).

Probiotic Effects. As a probiotic, Streptococcus thermophilus supports digestive health and boosts the immune system by stimulating antibody production and enhancing resistance to intestinal infections (3).

Production of Natural Antibiotics. It produces substances with antibiotic properties that can help inhibit the growth of pathogenic bacteria (4).

Improvement of Texture and Flavor. In the production of fermented foods, it contributes to improving the texture and flavor, making the products more palatable.

Availability. Available in various forms, including as a starter culture for homemade yogurt and cheese production, as well as in probiotic supplements.

References_____________________________________________________________________

(1) Michel V, Martley FG. Streptococcus thermophilus in cheddar cheese--production and fate of galactose. J Dairy Res. 2001 May;68(2):317-25. doi: 10.1017/s0022029901004812. PMID: 11504394.

Abstract. The behaviour of Streptococcus thermophilus in combination with Lactococcus lactis subsp. cremoris or subsp. lactis mesophilic starters in experimental Cheddar cheese is reported. In a standard manufacturing procedure employing a 38 degrees C cook temperature, even very low levels (0.007%) of Str. thermophilus combined with normal levels of the mesophilic starter (1.7%) resulted in increased rates of acid production, the formation of significant amounts of galactose (approximately 13 mmol/kg cheese), and populations nearly equivalent to those of the mesophilic lactic starter in the curd before salting. At a 41 degrees C cook temperature, the Str. thermophilus attained a higher maximum population (approximately log 8.2 colony forming units (cfu)/g) than the Lc. lactis subsp. cremoris (approximately log 6.8 cfu/g) and formed more galactose (approximately 28 mmol/kg). Lactobacillus rhamnosus, deliberately added to a cheese made using Str. thermophilus starter and which contained 24 mmol galactose/kg at day one, utilized all the galactose during the first 3 months of cheese ripening. Adventitious non-starter lactic acid bacteria had the potential to utilize this substrate too, and a close relationship was demonstrated between the increase in this flora and the disapearance of the galactose. Some possible consequences for cheese quality of using Str. thermophilus as a starter component are discussed.

(2) Uriot O, Kebouchi M, Lorson E, Galia W, Denis S, Chalancon S, Hafeez Z, Roux E, Genay M, Blanquet-Diot S, Dary-Mourot A. Identification of Streptococcus thermophilus Genes Specifically Expressed under Simulated Human Digestive Conditions Using R-IVET Technology. Microorganisms. 2021 May 21;9(6):1113. doi: 10.3390/microorganisms9061113. 

Abstract. Despite promising health effects, the probiotic status of Streptococcus thermophilus, a lactic acid bacterium widely used in dairy industry, requires further documentation of its physiological status during human gastrointestinal passage. This study aimed to apply recombinant-based in vivo technology (R-IVET) to identify genes triggered in a S. thermophilus LMD-9 reference strain under simulated digestive conditions. First, the R-IVET chromosomal cassette and plasmid genomic library were designed to positively select activated genes. Second, recombinant clones were introduced into complementary models mimicking the human gut, the Netherlands Organization for Applied Scientific Research (TNO) gastrointestinal model imitating the human stomach and small intestine, the Caco-2 TC7 cell line as a model of intestinal epithelium, and anaerobic batch cultures of human feces as a colon model. All inserts of activated clones displayed a promoter activity that differed from one digestive condition to another. Our results also showed that S. thermophilus adapted its metabolism to stressful conditions found in the gastric and colonic competitive environment and modified its surface proteins during adhesion to Caco-2 TC7 cells. Activated genes were investigated in a collection of S. thermophilus strains showing various resistance levels to gastrointestinal stresses, a first stage in the identification of gut resistance markers and a key step in probiotic selection.

(3) Vitetta L, Llewellyn H, Oldfield D. Gut Dysbiosis and the Intestinal Microbiome: Streptococcus thermophilus a Key Probiotic for Reducing Uremia. Microorganisms. 2019 Jul 31;7(8):228. doi: 10.3390/microorganisms7080228. 

Abstract. In the intestines, probiotics can produce antagonistic effects such as antibiotic-like compounds, bactericidal proteins such as bacteriocins, and encourage the production of metabolic end products that may assist in preventing infections from various pathobionts (capable of pathogenic activity) microbes. Metabolites produced by intestinal bacteria and the adoptions of molecular methods to cross-examine and describe the human microbiome have refreshed interest in the discipline of nephology. As such, the adjunctive administration of probiotics for the treatment of chronic kidney disease (CKD) posits that certain probiotic bacteria can reduce the intestinal burden of uremic toxins. Uremic toxins eventuate from the over manifestation of glucotoxicity and lipotoxicity, increased activity of the hexosamine and polyol biochemical and synthetic pathways. The accumulation of advanced glycation end products that have been regularly associated with a dysbiotic colonic microbiome drives the overproduction of uremic toxins in the colon and the consequent local pro-inflammatory processes. Intestinal dysbiosis associated with significant shifts in abundance and diversity of intestinal bacteria with a resultant and maintained uremia promoting an uncontrolled mucosal pro-inflammatory state. In this narrative review we further address the efficacy of probiotics and highlighted in part the probiotic bacterium Streptococcus thermophilus as an important modulator of uremic toxins in the gut of patients diagnosed with chronic kidney disease. In conjunction with prudent nutritional practices it may be possible to prevent the progression of CKD and significantly downregulate mucosal pro-inflammatory activity with the administration of probiotics that contain S. thermophilus.

(4) Tarrah A, Treu L, Giaretta S, Duarte V, Corich V, Giacomini A. Differences in Carbohydrates Utilization and Antibiotic Resistance Between Streptococcus macedonicus and Streptococcus thermophilus Strains Isolated from Dairy Products in Italy. Curr Microbiol. 2018 Oct;75(10):1334-1344. doi: 10.1007/s00284-018-1528-7. 

Abstract. Streptococcus thermophilus and S. macedonicus are the only two species of the genus related to food productions so far known. In the present study, eight S. thermophilus and seven S. macedonicus strains isolated from dairy environments in Italy were compared in order to evidence possible species-specific technological characteristics. Their capability to use lactose, galactose, fructose, and glucose, sugars commonly present in foods and two carbohydrates considered as prebiotics, xylose and inulin, along with the respective growth kinetics were studied. Results showed a luxuriant growth on lactose and different behaviors on galactose, glucose, and fructose. No growth on inulin and xylose was recorded, which is a positive feature for strains intended to be used as starter cultures. Growth parameters, namely, λ, µmax, and Nmax, were estimated by using the Gompertz model. Antibiotic resistance to 14 drugs revealed an overall similar behavior between the two species with only a marked difference regarding gentamycin. Antimicrobial activity was also tested against six deleterious bacterial strains, but none of the strains evidenced inhibitory capabilities. The results presented here could be helpful to compare technological potentialities of the two species and to choose strains of the most suitable species for selected microbiological food transformations.