What connects layers of peptidoglycan to each other?

Peptidoglycan layers are connected by teichoic acids. Teichoic acids are linear polymers made up of polyglycerol or polyribitol substituted with phosphates and a few amino acids and sugars. These teichoic acid polymers run perpendicular to the peptidoglycan layers connecting them to each other.

The presence of teichoic acid is unique to Gram-positive bacteria, which have multiple layers of peptidoglycan in their cell wall. Gram-negative bacteria have only one layer of peptidoglycan in their cell wall