WHAT HAVE I LEARN?
This week we will learn about the bacterial staining. A stain is an organic compound which containing benzene ring, a chromophore and an auxochrome group. Acidic stains are anionic, which means that on ionization of the stain, the chromogen ( coloured compound) portion which is negatively charged will bind to the positively charged cellular component, protein. For example, picric acid. Basic stains are cationic, which mean that on ionization of the stain, the chromogen portion which is positively charged will has strong affinity for the nucleic acids, negatively charged cellular component. For example, methylene blue, malachite green, crystal voilet and carbolfuchsin. Simple staining is use for visualization of morphological shape and arrangement which differential staining use in separation into groups and also visualization of structure.
We first start with the bacterial smears. The preparation including the heat fixation which fixed the bacterial proteins on the glass surface by rapid passing the air- dried smear few times over flame of Bunsen burner. Next we go on on simple staining. Simple staining only stained the bacterial smear with single reagent. The bacterial shapes and arrangement can be clearly seen under microscope after staining. Lastly, the negative staining. The negative staining require acidic stain which include India ink or nigrosin. These negatively charged chromogen will not penetrate the cell thus give image of unstained cells viewed against the coloured background which is darker in colour. Negative staining is more to use in determine whether an organism possesses a capsule.
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