- Question Answer
- Assertion Gram-negative bacterial do not retain the stain when washed with alcohol.
. Assertion Gram-negative bacterial do not retain the stain when washed with alcohol.
Reason The outer face of the outer membrane of Gram-negative bacteria contains lipopolysaccharides, a part of which is integrated into the membrane lipids.
Solution: Gram staining technique was developed by the Danish Bacteriologist Hans Christian Gram in 1884. It is a very useful procedure and on the basis of it bacteria can be lassified into :
(a) Gram positive, i.e.,m those which give (+) ve test with gram stain.
(b) Gram negative, i.e, those which give (-)ve test with gram stain. The steps involved in gram staining are summarised as :
The composition of bacterial cell wall is the basis for gram staining technique. The cell wall if gram (-) ve bacteria contain alcohol soluble lipids (lipopolysaccharides) while the cell wall of gram (+)ve bacteria lacks these lipids, therefore, retains the crystal violet-Iodine complex used.