The teichoic acids are polyanionic glycopolymers that are part of the cell wall of Gram negative bacteria. The constituent monomers of these acids are the polyalcholes glycerol and ribitol, which are linked through phosphodiester bonds..
They have been classified into teichoic acids and lipolyteichoic acids based on their composition and location in the bacterial cell. The former interact with the peptidoglycan present in the cell wall, while the latter anchor to the lipid bilayer thanks to its association with lipids..
Many functions are those that have been attributed to these polymers, among which are those of providing rigidity to the wall and providing a high density of negative charge. The latter can help speed up many physiological processes such as increased mobilization of divalent ions such as magnesium..
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Teichoic acids are polymers of a polyol, which may well be glycerol or rubitol.
These types of polymers are called polyanionic glycopolymers because of their richness in negatively charged groups. In them, the monomers of the polyol are linked through phosphodiester bonds and associated with alanine esters and glycosyl groups..
These acids have been described as important constituents of the cell wall of gram positive bacteria, characterized by having a thick layer of peptidoglycan.
Peptidoglycan is a polymer made up of N-acetyl muramic acid and N-acetylglucosamine molecules. Teichoic acids bind covalently to each residue of N-acetyl muramic acid, giving the wall a high density of negative charge..
Additionally, it has been found that certain teichoic acids can bind to some lipids present in the plasma membranes in bacteria. The product of this union has been called lipoteichoic acid.
At this point, it is important to mention that the different genera and existing species of great positive bacteria differ in the type of teichoic acids that are associated with their walls and membranes..
Therefore, the latter have been used as useful markers for the serological classification and identification of genera and species of Gram positive bacteria..
Studies on the function of the polyalcohols cytidine diphosphate-glycerol and cytidine diphosphatoribitol (constituents of teichoic acids) made it possible to detect these acids for the first time in the membrane of Gram positive bacteria in 1958..
In fact, the isolation of these polyalcohols made it possible to show that both ribitol phosphate and glycerol-phosphate are forming polymers. These were called teichoic acids by the Greek "teichos" which means wall.
This general designation of teichoic acids has undergone modifications as structural variations have been discovered in these polymers and different subcellular locations..
In the first instance, the terms polyribitholphosphate teichoic acids and polyglycerolphosphate teichoic acids were used to refer to the type of alcohol that made up the polymer..
However, as polyglycerolphosphate polymers were found to be associated with membranes of bacteria without cell walls, they were called membrane teichoic acids..
Several years later, when amphiphilic complexes of teichoic acids were detected covalently bound to membrane glycolipids, the name of lipoteichoic acids arose..
Now, at present, two final names persist: teichoic acids and lipoteichoic acids. The first refers to those that interact with the peptidoglycan present in the bacterial walls and the second refers to those that anchor to the plasma membrane through hydrophobic interactions..
Teichoic acids that have been described as important constituents of the cell wall of Gram positive bacteria perform numerous functions at this level..
In addition to giving the wall greater structural support, they provide it with a high negative charge density. This last feature gives these bacteria the ability to:
- Increase the ability to adhere to substrates. This thanks to the establishment of electrostatic interactions between the negatively charged groups of polyalcoles and the positively charged residues present in extracellular molecules..
- Facilitate and control the mobilization of divalent cations such as magnesium, which, due to their positive charge, are attracted more strongly towards the wall.
Another function attributed to teichoic acids is to provide tolerance to thermal stress and osmotic stress. This is due to the fact that it has been seen that bacteria lacking teichoic acids cannot withstand high temperatures or grow in very saline environments..
Furthermore, it appears that teichoic acids alone or in combination with peptidoglycan function as activators of the immune response. That is, they act as immunogens.
Staphylococcus aureus is a Gram positive bacterium distributed throughout the world, responsible for causing a wide variety of skin, respiratory and blood diseases.
The teichoic acids associated with the wall of this bacterium give it properties that allow it to increase its pathogenicity..
Some of these properties are:
- The high adhesion capacity to epithelial and mucosal cells of the organism that they infect, allowing a rapid and effective invasion.
- Resistance to the action of β-lactam antibiotics such as penicillin.
- Increase in the acquisition of resistance genes by horizontal transfer.
On the other hand, it is important to emphasize that in the same way that they enhance pathogenicity, they are highly immunogenic. That is, they are capable of rapidly activating the immune response of the host to which they infect.
In this sense:
- They stimulate the rapid production of antibodies.
- They activate the complement and favor the rapid migration of the cells of the immune system to the site of infection.
Finally, it is relevant to mention that the glycosylation of these teichoic acids also constitutes a determining factor of pathogen-host interactions..
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