Question

what is the gram stain method?
a) a staining method used to differentiate bacterial species into two groups
b) a staining method to identify bacterial dna using fluorescent staining reagents
c) a staining method used to identify acid - fast bacteria
d) a staining method used to identify the presence of endospores

Explanation:

The Gram stain method is a widely - used technique in microbiology. It is based on the differences in the cell wall structure of bacteria. Bacteria are first stained with crystal violet (a primary stain). Then, a mordant (iodine) is added. After that, a decolorizing agent (usually ethanol or acetone) is used. Finally, a counter - stain (safranin) is applied. Gram - positive bacteria retain the crystal violet - iodine complex (appear purple or violet) because they have a thick peptidoglycan layer in their cell walls. Gram - negative bacteria lose the primary stain during decolorization and take up the counter - stain (appear pink or red) as they have a thin peptidoglycan layer and an outer membrane. So, it is a staining method used to differentiate bacterial species into two groups (Gram - positive and Gram - negative).
Option b is incorrect because the Gram stain is not specifically for identifying bacterial DNA with fluorescent reagents. Option c is incorrect as the acid - fast stain (e.g., Ziehl - Neelsen stain) is used to identify acid - fast bacteria (like Mycobacterium tuberculosis). Option d is incorrect because the endospore stain (e.g., Schaeffer - Fulton stain) is used to identify the presence of endospores.

Answer:

A. A staining method used to differentiate bacterial species into two groups