Prescott's Microbiology 8th Edition by Joanne Willey, Linda Sherwood, Christopher J. Woolverton, Lansing Prescott, John Harley, Donald Klein

Exercise 4

What other differential staining procedures can be useful in identifying a bacterium? What information do they provide?

Step 1 of 2

Other differential staining procedures include acid-fast staining, endospores staining, capsule staining, and flagella staining.

1. Acid-fast staining is used to identify Mycobacteria. The Mycobacteria have a special cell wall that does not look like a gram-negative or a gram-positive cell wall. In the acid-fast staining protocol, fixed bacteria are stained with fuchsin by using high heat and phenol. Then acidified alcohol is used to wash the stain out. Mycobacteria have a mycolic acid cell wall that retains the fuchsin stain whereas other bacteria will have the stain washed out by the acid.

2. Endospore staining uses heat to infuse the dye (malachite green) into the endospore. An endospore is a bacterial structure, which allows the bacteria to survive in very dry, harsh conditions. Only certain bacteria produce endospores. Some of these bacteria, like Bacillus anthracis or Clostridium botulinum, are medically important.

3. Capsule staining shows the presence of capsule, which is an extracellular structure. Capsule is produced by many bacteria and some fungi and is an extracellular, polysaccharide matrix. Capsule provides protection from antibiotics as well as from components of the immune system and plays a role in virulence for some pathogenic bacteria. India ink or nigrosin dye is mixed with the cells. Cells that express capsule do not stain with the dye.

4. Flagella staining allows for the visualization of flagella on a cell. The number and localization of the flagella can be determined using this stain. Flagella are extracellular organelles that allow bacteria and archaea to swim. Flagellar structures must be first thickened with a mordant and then stained with pararosaniline or basic fuchsin.