Final answer:
Methylene blue is a secondary counterstain used in microbiological staining techniques to increase specimen contrast and does not sterilize equipment or stain only prokaryotic cells. It's essential for identifying bacteria, such as in the Ziehl-Neelsen and Kinyoun staining methods for acid-fast bacteria.
Step-by-step explanation:
Methylene blue is a stain used in microbiology to aid in the observation of cells under a microscope. It functions as a secondary counterstain in procedures like the Ziehl-Neelsen and the Kinyoun methods, which are specific for identifying acid-fast bacteria (AFB). In these, non-acid-fast cells are rendered blue, providing a visual contrast to the red or pink acid-fast bacteria. This contrast is crucial for the diagnosis of diseases caused by AFB.
In a simple stain setup, methylene blue, which is a cationic dye, binds to bacterial cells due to attraction by charge, making them easier to observe against a bright background. It increases the contrast in specimens, helping to differentiate bacteria from their surroundings. It does not sterilize the tool used for sample collection, such as a toothpick, nor does it exclusively stain prokaryotic cells, as it can also be used for staining eukaryotic cells.
In summary, methylene blue is a versatile dye used in various staining techniques in microbiology to enhance visibility and distinguish between different microorganisms and cellular structures.