Gram Positive Cocci Archives • Page 6 of 6 • Microbe Online

Many gram-positive bacteria have acidic components called teichoic acids embedded in their cell wall. Teichoic acids were discovered in 1958 by Armstrong and co-authors. Gram Positive cell wall with Teichoic acid The term teichoic acid encompasses a diverse family of cell surface glycopolymers containing phosphodiester-linked polyol repeat units. Teichoic acids are fibers of glycerol phosphate (glycerol teichoic acid) or ribitol phosphate (ribitol teichoic acid). Teichoic acids are located in the outer layer of certain Gram-positive bacteria (such as Staphylococci, Streptococci, Lactobacilli, and Bacillus spp). So far teichoic acids have not been present in Gram-negative Bacteria. Types of Teichoic Acids Lipoteichoic acids (LTAs): Teichoic acids that are covalently linked to the lipid in the cytoplasmic membrane. Wall teichoic acids (WTAs): Teichoic acids that are covalently attached to muramic acid in the wall peptidoglycan. Wall Teichoic acid and Lipoteichoic acid Wall teichoic acids are intimately involved in many aspects of cell division and are essential for maintaining cell shape in rod-shaped organisms. WTAs are required for ß-lactam resistance in methicillin-resistant S. aureus (MRSA), and they modulate susceptibility to cationic antibiotics in several organisms. Functions of Teichoic Acids Teichoic acids play a role in pathogenesis by promoting adherence to host tissues. For example, S. pyogenes adhere to pharyngeal epithelium via pili composed of lipoteichoic acid and M protein. They induce septic shock through the same pathways as does endotoxin (lipopolysaccharide ) in Gram-negative bacteria. Lipoteichoic acids play a role in the induction of septic shock by inducing cytokines such as interleukin-1 (IL-1) and tumor necrosis factor (TNF) from macrophages. Teichoic acids are polymers with high negative charge so they can serve as a cation-sequestering mechanism. Teichoic acids bind Ca2+ and Mg2+ for their eventual transport into the cell. Structure of Teichoic Acid TAs are glycopolymers rich in phosphates present in the peptidoglycan layers of Gram-positive bacteria (pathogenic and nonpathogenic). The structure of teichoic acid varies based on its type. Below is a brief description of the wall- and lipo-teichoic acid structure. Structure of Wall Teichoic Acid (WTA) In WTAs, the anionic glycopolymers attach covalently to peptidoglycan by a phosphodiester linkage to the C6 hydroxyl of the N-acetyl muramic acid sugars. These form 60% of the total cell wall of Gram-positive organisms. Structure of Teichoic acid from Micrococcaceae The chemical structures of WTAs vary in different organisms. However, the typical structure comprises ManNAc (β1→4)GlcNAc disaccharide with one of the three glycerol phosphates attached to the C4 hydroxyl of the ManNAc residue. A much longer chain of glycerol- or ribitol-phosphate repeats (the main chain) follows this chain. For example, Staphylococcus aureus strains primarily have poly (ribitol phosphate), but Bacillus subtilis may have both poly(glycerol phosphate) or poly (ribitol phosphate), depending on the strains. The tailoring of hydroxyls on the glycerol- or ribitol phosphate repeats occur with cationic D-alanine esters and monosaccharides like glucose or N-acetylglucosamine. The presence of WTAs and the particular modifications found on the organisms profoundly affect the physiology of Gram-positive organisms, their interactions with hosts, and their susceptibility to antibiotics. Structure of Lipoteichoic Acid (LTA) Lipoteichoic acid LTA are the macro amphiphiles possessing alditol phosphate residues in their hydrophilic moiety. There are two types of present: poly(glycerol phosphate) and poly-(ribitol phosphate). The poly(glycerol phosphate) is the standard type. A glycolipid (in most cases) forms the hydrophobic moiety of the LTA—the hydrophilic part links to the glycolipid by a phosphodiester bridge. The glycolipid anchors all the molecules in the cytoplasmic membrane. References Madigan Michael T, Bender, Kelly S, Buckley, Daniel H, Sattley, W. Matthew, & Stahl, David A. (2018). Brock Biology of Microorganisms (15th Edition). Pearson. Swoboda, J. G., Campbell, J., Meredith, T. C., & Walker, S. (2010). Wall teichoic acid function, biosynthesis, and inhibition. Chembiochem : a European journal of chemical biology, 11(1), 35–45. https://doi.org/10.1002/cbic.200900557 Holst, O., & Müller-Loennies, S. (2007). Microbial Polysaccharide Structures. Comprehensive Glycoscience, 123–179. doi:10.1016/b978-044451967-2/00004-0