BT102 Assignment 2 Solution 2021
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Solution
Answer: *Types of bacteria on the basis of their cell wall.*
The Gram stain characterizes bacteria based on the structural characteristics of their cell walls. By
combining morphology
and Gram-staining, most bacteria can be classified as belonging to one of 4 groups (Gram-positive cocci,
Gram-positive bacilli,
Gram-negative cocci, and Gram-negative bacilli).The gram-positive cell wallGram-positive cell walls are
thick and the Peptidoglycan (also known as murein) layer constitutes almost 95% of the cell wall in some
grampositive bacteria.
The gram-negative cell wall Gram-negative cell walls are much thinner than the gram-positive cell walls,
and they contain a second plasma membrane superficial to their thin peptidoglycan layer, in turn
adjacent to the cytoplasmic membrane. Gram-negative bacteria are stained as pink color.Staining
techniques step by step are a described as follow:1) Basic Dyes or Positive Staining in this staining
following basic dyes are used➢ Crystal violet➢ Methylene blue➢ Malachite green ➢ Safranin Acidic Dyes
or Negative Staining: in this staining following acidic dyes are used• Eosin• Acid fuchsin2) Simple
Staining • in simple staining a single stain is used. The Stain is washed off and Microbes seen under the
microscope. Methylene blue Carbolfuchsin Crystal violet, and safranin are used in this stainingand
sometimes a mordant is added.’ 3) Differential Staining: is also known as Gram Staining •Differential
stains react differently with different kinds of bacteria. . Most common is Gram staining, Developed
1884, by Hans Christian Gram Gram Staining.Gram Staining Crystal violet is added as Primary stain then
Crystal violet is washed off. After, iodine is added to enhance binding. Here iodine is act as Mordant.
And the slide is washed off with Decolorizing agent alcohol• Gram positive bacteria retain crystal violet •
Gram negative bacteria appear colorless. . Crystal violet and iodine make a complex in the cytoplasm •
Peptidoglycan layer is thicker in Gram positive bacteria and CV-I is retained. Alcohol is rinsed off and
stained withCounterstain safranin. • The smear is washed again. • Blotted dry and examined
microscopically.4) Acid-Fast Staining • Some bacteria such as Mycobacterium has a waxy material in
their cell wall known as Mycolicbacterium has a waxy material in their cell wall known as Mycolic acid •➢
Mycobacteria are lipophilic, not easy to stain Once stained, are resistant to counterstain Carbol fuchsin
as primary stain ➢ Heat is used to enhance penetration of the stain. ➢ Acid alcohol is decolorizer. ➢
Methylene blue is counterstain. 5) Special Staining: Used for coloring specific parts of an organism like
Endospore , Flagella and ,Capsule 6) Endospore Staining: Endospore: A resistant dormant structure
within a cell• Position of the Endospore varies within the cell• Appear as a clear hallo in Gram stained
smears• Heated to steaming for 5 min.• Washed with water.
• Counterstained with safranin.
