Streptococcus thermophilus characteristics, morphology

Philip Kelley

Streptococcus thermophilus It is a lactic acid bacterium of importance in the food industry. This microorganism is used as an initial culture for the production of fermented dairy products, such as yogurt and cheese..

S. thermophilus it is particularly well adapted to milk, due to its ability to use lactose, a preferential carbohydrate that is present in high and non-limiting concentrations in this product.

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It has been seen that the consumption of yogurt brings beneficial effects to humans due to the metabolic properties of S. thermophilus. Among these properties is the hydrolyzing activity of lactose present in yogurt and in the gastrointestinal tract, thus reducing the symptoms of intolerance to this carbohydrate..

Even if S. thermophilus is closely related to other pathogenic streptococci (such as S. pneumoniae Y S. pyogenes), is classified as a non-pathogenic species. This is explainable due to the characteristics of its genome. It has been studied and it is observed that 10% of the genes are inactive or are pseudogenes.

This means that many genes that are related to the virulence of pathogenic streptococci are either missing or imperfect genes..

S. thermophilus was considered a GRAS microorganism (generally recognized as safe) That is why it is currently widely used as a flavoring and texturizing agent.

Article index

  • 1 Features
  • 2 Taxonomy
  • 3 Morphology
  • 4 Health benefits
    • 4.1 Improves the condition of lactose intolerance
    • 4.2 Control of acute diarrhea
    • 4.3 Control of diarrhea caused by antibiotic therapy
    • 4.4 Control of gastritis and Helicobacter pylori infections
  • 5 References


S. thermophilus it is characterized by being facultative anaerobic. This means that it is capable of generating energy in the form of ATP, through aerobic respiration with the presence of oxygen. In the absence of oxygen they can produce ATP through fermentation.

As biochemical characteristics, it presents a positive Voges-Proskauer test and does not ferment arginine, mannitol or sorbitol. They do not support high concentrations of NaCl, which differentiates it from the Enterococcus and Lactococcus genera.

S. thermophilus it is an acidophilic, homofermentative bacterium. Therefore, when added to milk, it produces the rapid acidification of the medium by the fermentation of lactose, favoring coagulation..

One problem that yogurt and cheese producers present is that S. thermophilus is often susceptible to phage attack, which can result in slow lactic acid fermentation and loss of product quality.

Taking into account that a dairy plant can process more than 5 × 105 liters of milk per day, phage problems can be very costly.

Due to this problem, it was possible to develop a PCR method that allows the detection of phages of S. thermophilus, providing a sensitive system useful for the dairy industry.


S. thermophilus belongs to the Bacteria Domain, Phylum Firmicutes, Bacilli Class, Lactobacillales Order, Streptococaceae Family, Streptococcus Genus, Species: thermophylus.

According to the classification based on the sequence of the 16SrRNA gene, Streptococcus thermophilus It is part of the Salivarius Group together with two more closely related species, which are  S. vestibularis Y S. salivarius.

All three species are found in the human oral cavity, although S. thermophilus has as natural habitat the bovine mammary mucosa and milk.


Streptococcus thermophilus seen at the Gram, it is observed as Gram-positive cocci with a diameter of 0.7 to 0.9 µm, which are arranged in pairs or chains of variable length.

Its cell wall is composed of N-acetylglucosamine (NAG) and N-acetylmuran acid (NAM), linked by ether bonds. This structural characteristic gives it the property to withstand high temperatures, with an optimal growth rate of 45 ° C..

This is useful for many industrial dairy fermentations that require high process temperatures. On the other hand, S. thermophilus is an immobile, non-spore-forming bacterium that lacks cytochrome oxidase and catalase enzymes.

S. thermophilus It contains two unique peptidases, oligopeptidase and aminopeptidase. These enzymes catalyze the cleavage of specific amino acids from the end of a polypeptide..

Its proteolytic capacity makes it useful for the food industry by being able to hydrolyze milk protein (casein), although it does so in a very poor way, making it necessary to include other probiotics.

On the other hand, the exopolysaccharides produced by this bacterium are essential to generate the texture of fermented dairy products and the organoleptic properties..

For example, S thermophilus it has the ability to hydrolyze hydrophobic peptides. This property is essential to reduce the bitter taste in cheese..

Another characteristic provided by exopolysaccharides of the heteropolysaccharide type produced by S. thermophilus, It is the greater capacity that they have to bind to water during the maturation process of cheeses.

This ensures that water is retained by the final product, providing better performance..

Health benefits

Among the benefits obtained by consuming foods that contain the probiotic S. thermophilus is it so:

Improves lactose intolerance condition

For people suffering from lactose intolerance, it is healthy to consume S. thermophilus.

This bacterium converts lactose into lactic acid through an enzyme called β-galactosidase. This facilitates digestion and avoids the typical discomforts of this condition, such as flatulence, stomach pain and vomiting..

Control of acute diarrhea

Likewise, it is an excellent adjuvant in the treatment of acute diarrhea caused by pathogenic bacteria..

In this sense, probiotics act as antagonists of pathological processes. They do this through competition with pathogens for nutrients and binding to host cells..

In addition, probiotics can produce antioxidants and antimicrobial substances that alter the local pH, stimulate mucin production, improve the functions of the intestinal barrier and modify toxins derived from pathogens..

Control of diarrhea caused by antibiotic therapy

It is known that broad-spectrum antibiotic therapies can destroy the intestinal microbiota, causing an imbalance in it, where drug-resistant microorganisms proliferate disproportionately. This causes episodes of diarrhea, among other discomforts..

It is believed that S. thermophilus protects the small intestine, helping to restore lost gastrointestinal microbiota. 

This microorganism favors the proliferation of other probiotic bacteria, while preventing the growth of pathogenic and opportunistic microorganisms.

S. thermophilus It almost never acts alone, as it is better when it is accompanied by other similar bacteria. It works in perfect synergy with Lactobacillus and Bifidobacteria, where they all produce cofactors that the others need to proliferate..

Control of gastritis and infections by Helicobacter pylori

Another benefit that is attributable to S. thermophilus it is its power to control gastritis. Also, used alongside Lactobacillus delbrueckii helps eradicate bacteria Helicobacter pylori. 

Its contribution consists in reducing the secondary effects caused by treatment for the eradication of the H. pylori, which increases the tolerability and efficacy of the therapy.

The mechanism of action of probiotics in this regard can be attributed to their ability to stimulate the immune mechanisms of the mucosa.

These include activation of local macrophages, increased antigen presentation, and modulation of cytokine profiles..

On the other hand, it has been shown that yogurt supplemented with probiotics (L. acidophilus, L. bulgaricus, B. lactis, S. thermophilus) reduces colonization by H. pylori, TNF-α expression, gastric inflammation, and metaplasia.


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