Why Teichoic acid present only in gram positive bacteria and not gram negative bacteria?

Teichoic acids aren’t found in Gram-negative bacteria because they lack it or in other word it how there structures are . They are a major constituent of the Gram-positive cell wall and they contribute to wall stability in those organisms. Gram negative bacteria have a completely different structure, with an outer membrane that almost always contains lipopolysaccharide. Alterations in the structure and properties of either LPS (in Gram-negatives) or teichoic acid (in Gram-positives) can increase the resistance of those microbes to environmental stresses. You can easily Google these differences for yourself, but there are lots of subtle differences that can have major effects, depending on the specific bacterium you are talking