21. Explanation
๏ Bacterial/fungal capsules are non-ionic, so neither acidic nor
basic stains will adhere to their surfaces. Therefore, the best way
to visualize them is to stain the background using an acidic stain
and to stain the cell itself using a basic stain. We use India ink
and Gram crystal violet.
๏ Negative staining employs the use of an acidic stain and, due to
repulsion between the negative charges of the stain and the
bacterial surface, the dye will not penetrate the cell. In negative
staining, the results yield a clear cell with a dark background.
33. Explanation
๏ To stain all microorganisms in a uniform color for
easier observation
๏ Using a single stain for the staining. So we can observe
all the organism in same color.
39. Explanation
๏ Acid-fastness is an uncommon characteristic shared by
the genera Mycobacterium and Nocardia (weakly acid-
fast). Because of this feature, this stain is extremely
helpful in identification in diseases caused by acid-fast
bacteria, particularly tuberculosis and leprosy.
๏ Nocardia is typically weakly acid-fast after traditional
carbol-fuchsin staining and positive on modified acid-
fast staining due to the presence of mycolic acid in the
cell wall. Unlike mycobacteria (also acid-fast positive),
Nocardia has a โbeadedโ appearance on acid-fast
staining.
43. Explanation
๏ Gram-variable organisms are those that cannot be
grouped as either negative or positive.
๏ This is due to the fact that these bacteria appear as a
combination of pink and purple cells when stained
with gram stain. As a result, they are categorised as
gram-variable bacteria.
๏ In cultures of Bacillus, Butyrivibrio, and Clostridium, a
decrease in peptidoglycan thickness during growth
coincides with an increase in the number of cells that
stain gram-negative. In addition, in all bacteria stained
using the Gram stain, the age of the culture may
influence the results of the stain.
45. Explanation
๏ Metachromatic granules (volutin) are the intracytoplasmic
granules which are used for storing the inorganic polyphosphate.
These large inclusion bodies can be generally seen in the
bacteria. These granules could be said as metachromatic as they
can take a colour different from that of the dye.
๏ Albert's stain test is used to stain and observe metachromatic
granules found in Corynebacterium diphtheriae. Albert stain is a
kind of differential stain used for staining and identifying
metachromatic granules. The granules appear purple-black when
exposed to Albert's stain and against the light green cytoplasm.
