What type of bacteria are characterized by a thick peptidoglycan layer in their cell wall?

Bacteria characterized by a thick peptidoglycan layer in their cell wall are classified as Gram-positive bacteria. The peptidoglycan layer in these bacteria is substantial and plays a vital role in maintaining cell shape and protecting the cell from osmotic pressure. During the Gram staining process, this thick layer retains the crystal violet dye, resulting in a purple color under the microscope.

In contrast, Gram-negative bacteria have a much thinner peptidoglycan layer and possess an outer membrane, which does not retain the crystal violet during staining, leading to a pink appearance instead. Acid-fast bacteria, such as Mycobacterium species, have a unique cell wall composition that includes mycolic acids, making them different from both Gram-positive and Gram-negative classifications. Mycoplasma bacteria lack a cell wall entirely, which sets them apart from the others in this context. Hence, the defining characteristic of a thick peptidoglycan layer is distinctly linked to Gram-positive bacteria.