What characterizes Gram Positive bacteria?

Gram-positive bacteria are primarily characterized by having a thick peptidoglycan layer in their cell wall structure. This thick layer retains the crystal violet stain used in the Gram staining procedure, causing these bacteria to appear purple under a microscope. The peptidoglycan provides structural support and protection, making it a significant feature in the classification of Gram-positive bacteria.

The presence of a thick peptidoglycan layer differentiates them from Gram-negative bacteria, which have a comparatively thin peptidoglycan layer and an additional outer membrane that can complicate the staining process. Additionally, while some Gram-positive bacteria can form spores, this is not a universal characteristic and does not define all Gram-positive species. Therefore, the defining characteristic remains the thick peptidoglycan layer.