BT102 assignment no2 solution 2021

BT102 assignment no2 solution 2021

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Question No. 1
What are different types of bacteria on the basis of cell wall and explain their staining techniques? (5×1=5)
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 wall
Gram-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 fuchsin
2) 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 staining and sometimes a
mordant is added.’
3) Differential Staining: is also known as Gram Staining •
Differential stains react differently we know that 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 with
Counterstain 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 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.


BT102 assignment no2 solution 2021

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