This week, the experiment that I have done is the gram-staining and acid-fast staining. Gram staining is a differential staining which determine whether the bacteria is gram positive or gram negative. All the bacteria is negatively charged. Gram staining differentiates the bacteria based on the cell wall which is the thickness of the peptidpoglycan. Gram positive bacteria has a thicker cell wall. Therefore, the crystal violet can be retained in the cell wall. Gram negative bacteria has a thinner cell wall. Therefore, it only retains the counterstain safranin. The procedure of gram staining is as followed. First, we gently flooded the smears with crystal violet and let stand for 1 minute. Then, we washed it with tap water. Next, we flooded the smears with Gram's iodine mordant and let stand for 1 minute. The smear is then later decolorized with 95% ethyl alcohol. The reagent was added drop by drop until the alcohol runs almost clear,showing only a blue tinge. Then, we gently washed the smear with tap water and counterstained with safranin for 45 seconds. It was gently washed again with tap water. The smear was then blotted dry with bibulous paper and examined under oil immersion. The gram staining were done for cultures of E. coli, S. aureus , B. cereus and the mixture of S.aureus and E. coli.
The next experiment which is experiment 10 is acid-fast staining. Acid-fast staining shows postive result for bacteria which has a thick, waxy wall that makes penetration by stains extremely difficult. The postive result is the smear of the bacteria will become pink in colour while negative results is the bacteria smear become blue in colour. The procedure of acid-fast stain is as followed. Smear of Mycobacterium smegmatis , Staphylococcus aureus and the mixture of both bacteria are prepared. The smears are then flooded with carbol fuchsin and placed over a beaker of water on a warm hot plate, allowing the preparation to steam for 5 minutes. Next, the smears were washed with tap water and heat slides must be cooled prior to washing. Then, decolorize the smears with acid-alcohol, adding the reagent drop by drop until the alcohol runs almost clear with a slight red tinge. The tap water was used to wash the smear. Finally, blot dry the smear with bibulous paper and the slides were examined under oil immersion.
The slides of gram-staining and acid-fast stain
The slides of Bacillus cereus under oil immersion
The slides of the mixture of S. aureus and E. coli
The slides of M. smegmastis under oil immersion
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