Explain Basic Stains (Cationic) - Types of Stains?
These are chloride or sulfate salts of coloured bases which on ionization give positively charged chromogen. As such, these have a strong affinity for the negative constituents of the cell (or these bind strongly to negatively charged component of the cell), e.g. nucleic acid. Surface of the bacterial cells is also negatively charged, so basic dyes are most often used in bacteriology. These work better at high pH (i.e. neutral / alkaline conditions). For this reason, basic dyes are made up in alkaline solution, e.g. Loeffler's methylene blue stain is prepared in KOH solution.The pH can affect the staining effectiveness by affecting the nature and degree of charge on cell components. Whereas, in neutral or alkaline environment, microbial cells are negatively charged, in acidic environment, these stain poorly with basic dyes. Different staining techniques can be used to visualize and study the different morphological characteristics of a cell.