Explain the methods of staining bacteria.

1. Simple staining
- Requires only a single dye and is not a complicated procedure
- Simple stains make all cells in a smear to appear more or less the same color
- Example of stains used – Malachite green, crystal violet, basic fuchsin and safranin
- Show size, shape and arrangement of cells

2. Differential staining
- Use two differently colored dyes – primary dye and counterstain to distinguish between cell types or parts.
- The techniques are more complex and require additional chemicals to produce required reaction.

3. Acid – fast staining
Some species of bacteria e.g. genus – mycobacterium, nocardia, parasite cryptosporidium, do not readily stain with simple stains
- They are stained by healing with carbolfuschin
- They are not easily decolorized by acid –alcohol hence are termed as acid fast
- The acid – fastness is due to the high lipid content (Mycolic acid) in the cell wall
- Acid fast microorganism retain the dye (carbolfuschin) and appear red
- Non – acid fast microorganism appear blue due to the counterstaining with Methylene blue after decolorizing by acid alcohol.

4. Endospore staining – structural stain
Bacteria is genera e.g. Bacillus and Clostridium produce a resistant structure capable of serving for long periods in an unfavorable environment and then giving rise to a new bacterial cell.
- This structure is called an Endospore since it develops within the bacterial cells
- The location and size of Endospore vary with the species and are of value in identifying bacteria
- Endospore position within the cells may be central, subs terminal or terminal
- Endospore do not stain easily but once stained, they strongly resist decolonization
- The Endospore are stained with malachite green
- Heat is used to provide stain penetration
- The rest of the cell is decolorized and counterstained a light red with safranin

5. Capsule staining
Many bacteria have slimy layer surrounding the cell wall referred to as a capsule
- The capsules composition and its thickness varies with individual bacterial species
- Polysaccharides, polypeptides and glycoproteins have all been found in capsules
- A pathogenic bacterium with a thick capsule is more violent than a strain with a little or no capsule since the activity capsule process the bacterial against the phagocytic activity of the hosts’ phagocytic cells. (The capsule stain is of some importance in clinical microbiology in diagnosis of bacterial /pneumonia and fungus Cryptococcus neoformans).
- Capsule staining employs two reagents
- The primary stain crystal violet, gives the bacterial cells, the capsule a dark purple color
- The capsule is non ionic and the primary stain cannot adhere
- Copper sulphate is the decolorized agent. It removes excess primary stain as well as color from the capsule
- Copper sulphate also acts as a countersign. Its absorbed into the capsule turning it light blue

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Kavungya answered the question on March 13, 2019 at 06:02