Gram staining is primarily used to determine the __________ of bacteria.

Gram staining is a critical laboratory technique used to classify bacteria based on their cell wall composition, which ultimately determines their Gram reaction. This procedure distinguishes bacteria into two major groups: Gram-positive and Gram-negative.

In a Gram stain, certain chemicals are applied to the bacteria that react differently depending on the structure of the bacterial cell wall. For instance, Gram-positive bacteria possess a thick peptidoglycan layer that retains the crystal violet dye used in the staining process, leading to a purple appearance. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane that does not retain the crystal violet during the staining process, resulting in a pink or red color after being counterstained.

Understanding the Gram reaction is vital in microbiology as it helps guide treatment decisions since Gram-positive and Gram-negative bacteria often respond differently to antibiotics. Thus, the primary purpose of the Gram stain is to determine the Gram reaction of bacteria, which reveals essential information about their biological characteristics and potential pathogenicity.