2. Staining of bacteria Bacterial staining is the process of coloring of colorless bacterial structural components using stains (dyes).The principle of staining is to identify microorganisms selectively by using dyes, fluorescence and radioisotope emission. Staining reactions are made possible because of the physical phenomena of capillary osmosis, solubility, adsorption, and absorption of stains or dyes by cells of microorganisms. Individual variation in the cell wall constituents among different groups of bacteria will consequently produce variations in colors during microscopic examination. Nucleus is acidic in character and hence, it has greater affinity for basic dyes. Whereas, cytoplasm is basic in character and has greater affinity for acidic dyes. There are many types of affinity explaining this attraction force:
1. 2. 3. 4. 5. 6 .
hydrophobic bonding reagent-cell interaction reagent-reagent interaction ionic bonding hydrogen bonding covalent bonding
Why are stains not taken up by every microorganism? Factors controlling selectivity of microbial cells are:
number and affinity of binding sites
rate of reagent uptake
rate of reaction
rate of reagent loss (differentiation or regressive staining)