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Gram Staining. Differential Stain. Differential Stain Distinguishes between different groups of bacteria based on their staining ability. How can you tell a bacterial cell from normal body cells when a possible infection has taken place?.

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Gram staining

Gram Staining

Differential Stain


  • Differential Stain

    • Distinguishes between different groups of bacteria based on their staining ability


How can you tell a bacterial cell from normal body cells when a possible infection has taken place
How can you tell a bacterial cell from normal body cells when a possible infection has taken place?

Problem presented to Hans Christian Gram (1884) while studying origins and causes (Ethiology) of pneumonia.

Couldn’t tell lung tissue from Streptococcus pneumoniae.

Developed Gram staining technique which is unique to bacterial cells due to their cell wall construction


How it works
How it works when a possible infection has taken place?

  • Gram positive bacteria have a thick layer ofPeptidoglycan(up to 90%)in their cell wall

  • Gram negative bacteria have a thinner layer (5- 20%)of this glycoprotein.

  • **Most cells are Gram -, except for Gram + bacteria, yeast and a few molds

Two derivatives of glucose

N-acetylglucosamine (NAG)

N-acetlymuramic acid (NAM).


Gram Positive when a possible infection has taken place?Gram Negative

Peptidoglycan

Porin

Lipids + LSP

Bilipid


How to do it
How to do it when a possible infection has taken place?

  • To a properly prepared, heat fixed smear, add 1 drop of the PRIMARY STAIN – Crystal Violet.

    Wait 1 minute and then rinse.

  • Add the MORDANT (intensifier) – Gram’sIodine.

    Wait 1 minute and rinse

  • DECOLORIZEwith Alcohol. Alcohol will remove stain from thin layers of peptidoglycan. Gram + hang onto stain while Gram – stain is washed away.

    1 second, rinse then 3 – 5 seconds and rinse SECONDARY STAIN or COUNTERSTAIN is then applied give decolorized stain a stain. Use Safranin.

    Wait 1 minute and rinse


The results
The results when a possible infection has taken place?

  • Gram Positive stains get colored by crystal violet and safranin so they will be purple.

  • Gram Negatives will only be stained now with Safranin and be pink.


Problems with the procedure
Problems with the procedure? when a possible infection has taken place?

  • Leaving the alcohol on too long. Will decolorize even Gram + cells

  • Too much of a rinse after the Crystal violet. Washes away all the stain

  • Not enough Mordant (Iodine) to intensify primary stain.

  • Old cultures. Cells break down due to not enough nutrients present.


Bacteria for lab
Bacteria for lab when a possible infection has taken place?

  • Bacillus subtilis

  • Aquaspirillum serpens

  • Branhamella catarrhalis

  • Sarcina aurantiaca

  • Serratia marcescans


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