Question

What is the principle, purpose of the gram stain and the applications of the acid-fast, spore, and negative stains? Explain!

Answer 1

Gram staining first discovered by the Hans Christian Gram in 1884 and it differentiates the bacteria into gram +ve and gram –ve based on the cell wall composition. When the bacteria (immobilized on the clear slide) stained with the crystal violet (primary stain) & fixed with the iodine (mordant). Due to the thick peptidoglycan in the cell wall the gram +ve resist to discoloration and do not take counterstain safranin, appear as purple or blue in color but due to thin peptidoglycan and outer membrane the gram –ve bacteria decolorized with the alcohol, take the counterstain safranin, appear in pink color.

Acid-fast staining also called Ziehl–Neelsen staining. It differentiates the bacteria into acid-fast and nonacid-fast based on the presence of complex lipids in the cell wall. the Acid-fast bacteria have complex micolipids in the cell wall but nonacid-fast bacteria do not have the complex micolipids. Acid-fast staining used to identify the bacteria like Mycobacterium tuberculosis & Mycobacterium avium and many protozoan pathogens which infect the fish can be identified.

Endospore staining also called Schaeffer–Fulton stain which is used to identify the vegetative cells and endospores. In Endospore staining, carbolfuchsin and nigrosin solutions are used.

Negative staining used for study the shape, size and morphological arrangement of bacteria