Chemical Compostion of Capsular Layer from Some Bacteria

Chemical Compostion of Capsular Layer from Some Bacteria

Chemical Compostion of Capsular Layer from Some Bacteria.

Bacteria	Capsular material	Structural subunit(s)
Bacillus anthracis	Polypeptide	D-glutamic acid
B. megaterium	Polypeptide and Polysaccharide	D-glutamic acid, amino sugars and sugars
B.circulans	Polysaccharide	Sugar and uronic acid
Pneumococcus sps.	Polysaccharide	Sugar, amino sugars, uronic acid
S.salivarius	Polysaccharide (Levan)	Sugars, amino sugars and uronic acid
Leuconostoc sps.	Polysaccharide (Dextran)	Glucose
Acetobacter xylinum	Polysaccharide (Cellulose)	Glucose
A.capsulatum	Polysaccharide (Dextrin)	Glucose
Enterobacter sps.	Polysaccharide	Glucose, fucose and glucuronic acid
Escherichia coli	Polysaccharide	Glucose, fucose and uronic acid

The capsules of bacteria present in animal tissues, blood, serous fluid and pus are often clearly stained when these materials are treated with one of the common stains such as carbol fuchsin, polychrome methylene blue, gram stain etc. Special capsule stain may be of little advantage in such cases. On the other hand, when laboratory cultures of bacteria are being examined the capsules are not stained by the ordinary method and special techniques, therefore, must be employed for their demonstration.
Bacterial tapsules are more easily confused with the artifact than any other structure pertaining to bacteria. Many times capsules are very thin and using negative or relief staining technique, they represent nearly as an unstained area around each cell.

They are many times mistaken with the slightly stained cell surrounding to retract from the cells on drying. For this reason, the best demonstration of capsule is achieved by using positive staining technique, which clearly differentiates capsule from cell.

However, capsules are best demonstrated using phase contrast microscope, where they appear as halo or clear ring around each cell. Preparation of smear in capsule staining technique is an important step. For better results, suspension of cells in 6% glucose or 1 % glucose in 10% serum is recommended for smear preparation.

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