Which of the following best describes the primary purpose of using a Gram stain in a microbiology laboratory?

• A. To measure the motility of bacterial cells
• B. To identify the presence of endospores in bacterial cultures
• C. To determine the oxygen requirements of bacteria
• D. To differentiate bacteria based on differences in their cell wall structure

Answer: (D)

Verified step by step guidance

1. Understand that the Gram stain is a differential staining technique used in microbiology to classify bacteria into two major groups: Gram-positive and Gram-negative.
2. Recognize that the primary basis for this differentiation is the structural differences in the bacterial cell wall, specifically the thickness of the peptidoglycan layer.
3. Recall that Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet stain, appearing purple under a microscope, while Gram-negative bacteria have a thinner peptidoglycan layer and do not retain the crystal violet, instead taking up the counterstain (usually safranin) and appearing pink or red.
4. Note that the Gram stain does not provide information about bacterial motility, presence of endospores, or oxygen requirements, which are determined by other specific tests or stains.
5. Conclude that the primary purpose of the Gram stain is to differentiate bacteria based on differences in their cell wall structure.