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

Gram-positive bacteria are distinguished from Gram-negative bacteria primarily by their cell wall structure. One of the key characteristics of Gram-positive bacteria is their thick peptidoglycan layer. This layer retains the crystal violet stain used during the Gram staining procedure, which results in Gram-positive bacteria appearing purple under a microscope.

The crystal violet stain binds tightly to the thick peptidoglycan, and upon the addition of iodine, forms a complex that is not easily washed out during the decolorization step. As a result, Gram-positive bacteria remain stained, making it easy to identify them in a laboratory setting.

In contrast, Gram-negative bacteria have a much thinner peptidoglycan layer, which does not retain the stain after decolorization, leading them to appear pink or red due to the counterstain used in the Gram staining process. Additionally, while Gram-positive bacteria generally do have a cell wall, Gram-negative bacteria possess an outer membrane that Gram-positive bacteria lack. The notion that all Gram-positive bacteria are resistant to all antibiotics is also incorrect, as susceptibility varies widely among different species and strains.