Final answer:
The Gram stain is used to identify bacteria with a significant amount of peptidoglycan in their cell walls, resulting in Gram-positive bacteria staining purple and Gram-negative bacteria staining red/pink.
Step-by-step explanation:
The stain used to identify bacteria with a large amount of peptidoglycan in their cell walls is the Gram stain. This differential staining technique uses a series of steps to distinguish between Gram-positive and Gram-negative bacteria based on their cell wall structure. Gram-positive bacteria have thick cell walls consisting of multiple layers of peptidoglycan, which retain the crystal violet stain, causing them to appear purple. Contrarily, Gram-negative bacteria have thinner peptidoglycan layers that do not retain the crystal violet, but instead take up the counterstain, safranin, appearing red/pink.