Differential Stains Flashcards
What is the purpose of differential stains in microbiology?
Differential stains are used to gather additional information about bacteria based on their chemical or structural properties.
Who developed the Gram stain, and when?
Christian Gram in 1884.
What are the two major groups of bacteria identified by the Gram stain?
Gram-positive and Gram-negative bacteria.
How do Gram-positive cell walls differ from Gram-negative cell walls?
Gram-positive walls have thick layers of peptidoglycan and teichoic acids, while Gram-negative walls have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides (LPS).
What are Gram-variable bacteria?
Bacteria that show both Gram-positive and Gram-negative reactions on a slide.
What is the sequence of reagents used in the Gram stain procedure?
Crystal violet, Gram’s iodine, ethanol, and safranin.
What is the first reagent used in the Gram stain procedure, and what is its effect?
Crystal violet; it turns all cells purple.
What is the purpose of Gram’s iodine in the Gram stain procedure?
It helps crystal violet adhere firmly to Gram-positive cell walls.
What happens during the ethanol step of the Gram stain?
Ethanol decolorizes Gram-negative cells, making them transparent, while Gram-positive cells remain purple.
What is the role of safranin in the Gram stain procedure?
Safranin stains transparent (Gram-negative) cells pink, while Gram-positive cells remain purple.
