National League for Nursing (NLN PAX) Practice Exam

A gram stain is primarily used for distinguishing between different kinds of bacterial cell walls, making the choice that highlights this function the correct one. This differential staining technique is fundamental in microbiology, as it allows for the identification of two major groups of bacteria: Gram-positive and Gram-negative. The procedure works by applying a series of stains to bacterial cells, which then react differently based on the structure and composition of their cell walls. Gram-positive bacteria retain the crystal violet stain and appear purple under a microscope due to their thick peptidoglycan layer. In contrast, Gram-negative bacteria do not retain the crystal violet during the process and take up the counterstain, appearing pink due to their thinner peptidoglycan layer and additional outer membrane.

By understanding these differences, healthcare professionals can make informed decisions regarding treatment options and understand the potential virulence of the bacteria involved. The gram stain is not used for separating bacteria from viruses, identifying toxins, or measuring cell density, which makes these other options less relevant to its primary purpose.