Microbiology Practice Exam

Gram-positive bacteria are characterized by having a thicker peptidoglycan layer in their cell wall compared to Gram-negative bacteria. This thicker peptidoglycan layer is crucial because it provides structural strength and rigidity, allowing the bacteria to maintain their shape and protect against environmental stress.

In addition to the thicker peptidoglycan layer, Gram-positive bacteria also lack an outer membrane, which is present in Gram-negative bacteria. This absence of an outer membrane allows the peptidoglycan to be more prominent and visible during the Gram staining process, resulting in a purple coloration due to the crystal violet dye being retained.

Mycoplasmas are unique in that they do not have a cell wall at all, and thus they do not possess peptidoglycan. Bacteria with capsules may have additional protective layers, but this does not necessarily pertain to the thickness of the peptidoglycan layer specifically. Therefore, the distinction lies in the fundamental structure of Gram-positive bacteria, making them the correct answer.