Certified Nurses Operating Room (CNOR) Practice Exam

What is the basis for the Gram stain procedure?

1. Color changes in proteins

2. Structural differences in nucleic acids

3. Physical and chemical properties of the cell wall

4. The shape and size of bacterial cells

The correct answer is: Physical and chemical properties of the cell wall

The Gram stain procedure is based on the physical and chemical properties of bacterial cell walls. Specifically, it relies on the differences in the composition and structure of the cell walls between Gram-positive and Gram-negative bacteria. Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet stain, making them appear purple under a microscope. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane that does not retain the crystal violet stain after the decolorization step. Instead, they take up the counterstain, such as safranin, which causes them to appear pink. This differential staining technique is crucial in microbiology for classifying and identifying bacteria, as the characteristics of the cell wall can affect not only the staining outcome but also the bacteria's susceptibility to antibiotics and other environmental factors. Therefore, understanding the chemical and physical properties of the bacterial cell wall is essential for performing the Gram stain correctly and interpreting the results accurately.