What characteristic distinguishes Gram-positive bacteria from Gram-negative bacteria?

The distinguishing characteristic that sets Gram-positive bacteria apart from Gram-negative bacteria is the greater amount of peptidoglycan in their cell walls. Gram-positive bacteria have a thick, multilayered peptidoglycan layer that can constitute up to 90% of the cell wall's composition. This thick layer is crucial for maintaining the structural integrity of the bacteria and plays a key role in their ability to retain the crystal violet stain used during Gram staining, leading to their characteristic purple appearance.

In contrast, Gram-negative bacteria have a much thinner peptidoglycan layer, which is located between the inner cytoplasmic membrane and an outer membrane that contains lipopolysaccharides. While Gram-negative bacteria do have peptidoglycan, it is significantly less in quantity compared to that of Gram-positive bacteria.

The presence of teichoic acids—found in the cell walls of Gram-positive bacteria—also contributes to their unique structural and functional properties, but the most fundamental distinction in terms of cell wall composition is the thicker peptidoglycan layer. Therefore, the correct answer highlights this critical difference between Gram-positive and Gram-negative bacteria.