How do Gram-positive bacteria differ from Gram-negative bacteria?

Gram-positive bacteria are characterized by having thick peptidoglycan layers in their cell walls. This structure not only provides rigidity and strength to the cell, allowing it to maintain shape, but it also plays a key role in the bacteria's ability to retain the crystal violet stain during the Gram staining process. The thick peptidoglycan layer traps the dye, resulting in a purple coloration when viewed under a microscope.

In contrast, Gram-negative bacteria have a much thinner peptidoglycan layer, situated between their inner cytoplasmic membrane and an outer membrane that contains lipopolysaccharides. This structural difference is critical in distinguishing between the two types during Gram staining, where Gram-negative bacteria do not retain the crystal violet and instead take up the counterstain, usually safranin, resulting in a pink appearance.

Understanding these differences is essential for microbiologists when determining bacterial classification, susceptibility to antibiotics, and potential pathogenicity, among other factors.