Studying of bacterial shape, cell wall, size, …. & so on, need to scope the bacteria under microscope. But you can not see any cells unless stain these cells, imagine that as a glass cup (cell) in front of white board (microscope field), you cannot see this cup unless pour a stain inside it. that is the same with bacterial staining and this cups (cell) differ in staining technique according to aim of study as simple stain, gram stain, spore stain, …. and so on.

About gram stain: depending on bacterial cell wall composition, the ability of bacteria to accept crystal violet with iodine to be a gram positive or not. Dividing of bacteria to gram positive or gram negative is very important in bacterial taxonomy, also in determine the type of antibacterial treatment with diseases.

For spore stain: bacteria form spores as a preservation tool for a live when exposure to environmental harsh conditions as high temperature, radiation, acidity, salinity, drought, …. and so on. Also, spores are forming within a stationary phase during bacterial growth. So it is necessary to detect spore forming bacteria in foods & dairy products to prevent spoilage through shelf life. Not any stain technique will be suitable with spore staining because it has to treat with heating to allow to stain enter in cells as you will see in lecture.