Explanation:
Gram staining is a widely used technique designed to distinguish between the bacteria on the basis of the composition of the cell wall of the bacteria.
The basis of differentiation is the color of the bacteria they attain after staining technique is performed that is gram-positive bacteria remain deep blue in color while gram-negative bacteria appear pinkish-red in color.
If the culture of the bacteria on which the test to be performed is of more age that is more than 24 hours of age then the bacteria cells lose their ability to retain the stain mainly the gram-positive bacteria. Also, the culture gets damaged after 24 hours.
Thus, fresh cultures are used for staining.
