9 julio, 2024

Streptococcus thermophilus: what it is, characteristics, morphology

what is the Streptococcus thermophilus?

Streptococcus thermophilus 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 utilize lactose, a preferential carbohydrate that is present in high and non-limiting concentrations in this product.

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.

Although S. thermophilus is closely related to other pathogenic streptococci (such as S. pneumoniae and 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 not present, or are present as imperfect genes.

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

Characteristics of S. thermophilus

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 in the presence of oxygen. In the absence of oxygen it can produce ATP through fermentation.

As a biochemical characteristic, it presents a positive Voges-Proskauer test and does not ferment arginine, mannitol or sorbitol. It does not support high concentrations of NaCl, which differentiates it from other genera enterococcus and Lactococcus.

S. thermophilus It is an acidophilic, homofermenting bacterium. For this reason, when added to milk, it produces rapid acidification of the medium due to lactose fermentation, favoring coagulation.

One problem faced by yogurt and cheese producers is that S. thermophilus it 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 expensive.

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

taxonomy of S. thermophilus

S. thermophilus belongs to the domain Bacteria, phylum Firmicutes, class Bacilli, order Lactobacillales, family Streptococaceae, genus streptococcusspecies thermophilus.

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

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

Morphology of the S. thermophilus

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

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

This is useful for many industrial dairy fermentations that require high temperatures in their processes. Besides, S. thermophilus it is an immobile, non-spore-forming bacterium that lacks the enzymes cytochrome oxidase and catalase.

S. thermophilus 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 as it is able to hydrolyze milk protein (casein), although it does so poorly, 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 milk products and the organoleptic properties.

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

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

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

Health benefits

Among the benefits obtained by consuming foods that contain the probiotic S. thermophilus are:

Improves the condition of lactose intolerance

For people who suffer 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 discomfort 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 attachment to host cells.

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

Control of diarrhea caused by antibiotic therapy

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

It is believed that S. thermophilus protects the small intestine, helping to restore the 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. youworks in perfect synergy with Lactobacillus and Bifidobacteria, where all produce cofactors that the others need to proliferate.

Control of gastritis and infections Helicobacter pylori

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

Its contribution consists in reducing the side effects caused by the treatment for the eradication of H pyloriwhich 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 mucosal immune mechanisms.

Among them is 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 pyloriTNF-α expression, gastric inflammation and metaplasia.

References

Montes M, García J. Streptococcus genus: a practical review for the microbiology laboratory Sick Infectious Microbiol Clin 2007;25 Suppl 3:14-20
Wikipedia contributors. Streptococcus thermophilus. Wikipedia, The Free Encyclopedia. August 25, 2018, 09:14 UTC. Available at: en.wikipedia.org/ Accessed September 7, 2018.
Ruggiero P. Use of probiotics in the fight against Helicobacter pylori. World J Gastrointest Pathophysiol. 2014; 5(4):384-391.

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