1. Describe and/or draw in detail the gram positive and the gram negative bacterial envelope. Then...

1. Describe and/or draw in detail the gram positive and the gram negative bacterial envelope. Then go on to describe all the steps of a gram stain. Conclude by explaining why the gram stain is such an important technique in the microbiology lab.

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Expert Solution

Gram positive envelope- cell walls are thick and primarily composed of peptidoglycan. In addition contain large amount of teichoic acid, polymer of glycerol or rabitol joined by phosphate group. Teichoic acid covalently connect with plasma membrane called lipoteichoic acid. Periplasmic space smaller than that of gram negative bacteria.

Gram negative envelope- it is much more complex that gram positive. Thin peptidoglycan layer sandwich between inner cytoplasmic cell membrane and outer membrane.

The details structure of both gram positive and gram negative cell wall are drawn in diagram:

Gram straining: it is a type of differential staining developed by Christian Gram in 1884. In 1st step the smear is stained with crystal violet: primary stain. As both the cell wall is negatively charged so they will take up the positively charged crystal violet (basic dye).

The iodine is added, it act as mordant which increases the interaction between the cell wall of bacteria and primary stain Crystal Violet.

Then smear is decolorized by ethanol or Acetone. This step generates a differential aspects of gram staining. In gram positive bacteria, due to thick layer of peptidoglycan the CV stain get trapped in the groove gram positive cell wall. But in case of gram negative bacteria, the thin peptidoglycan layer dissolved in decolorizer and primary stain losse.

Then Safranin is added as a counter stain, in which gram negative bacteria taken up and shows pink colour when observed in microscope. And gram positive bacteria shows Violet colour.

Steps of adding reagents in gram staining:

1st- Crystal Violet for 60 sec

2nd- Iodine for 60 sec

3rd- acetone/alcohol for 10-20 sec

4th- Safranin for 60 sec.

Gram staining is important technique in microbiology lab because by determining the gram character of the bacteria we can predict the cell wall structure and composition of an unknown bacterial sample. There by accordingly can perform various experiment. After knowing cell wall structure of unknown bacteria it can easily kills.

For further queries please do comment. Thank you ?

gladiator answered 1 year ago

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