Is peptidoglycan only found in bacteria?

Yes, peptidoglycan is only found in bacteria. It is a unique and essential structural component of the cell wall of many but not all species of bacteria. In bacterial species where it is present, peptidoglycan forms an inflexible cover surrounding the cytoplasmic membrane. Its main functions are to preserve the structure of the cell and act as a physical barrier against environmental stresses. 

Peptidoglycan is composed of glycosaminoglycan chains interlinked with short peptides. There are more than 100 different forms of this substance.