Question

1- Supposed when you are performing a gram stain procedure, you have reversed the the order of crystal violet and safranin , you stained with safranin first then, iodine , then wash with alcohol and then with crystals violet. What colors would (a) Escherichia Colin and (b) staphylococcus epidermids be? Provide a shorth explanation for your expected outcome

2- Suppose you performed a gram stain from a pure culture of bacteria and observed a field of red and purple bacilli. Adjacent cells were not always the same color. Provide an explanation for this observation

3- “Discuss why you should incubate bacterial plat upside down with the lid at the bottom”

Answer 1

1.

Gram staining technique is the procedure which is used to differentiate between Gram Negative and Gram Positive Bacteria on the basis of their cell wall composition.

Gram positive bacteria which appears purple is having thick layer of peptidoglycan where as Gram Negative bacteria which appears red is having a thin layer of peptidoglycan and the outermost covering is made up of lipopolysaccharide.

Crystal Violet stain imparts purple colour to Gram positive bacteria and imparts red colour to Gram Negative bacteria.

If the order of these two stains is Reversed, then Gram Positive Bacteria will appear red and Gram Negative bacteria will appear purple. Initially both of them will be red but after the addition of alcohol, Gram Negative bacteria will turn colourless. After the addition of cyrstal violet stain, Gram Negative bacteria will appear purple.

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