Gram Staining

Question 1

Steps of gram stain and fx and example of each

Answer 1

Primary stain: crystal violet
Stain all cell equally 60sec

Mordant: sear the crystal violet in the cell, retain color. Ex: iodine 60sec. Form cv-i2 complex

Decolorizing agent: washes off priary stain. Very important 10-12 sec.
For gram positive, the thick cell wall collapse and the cv-i2 gets trapped in, thus gram positive retain color and is purple.
For gram negative, the thin cell wall is destroyed and cv-i2 escape and thus gram neg loses color

Counter stain: dye to contrast primary stain. For gram negative who loss primary color, it pocks THIS dye up and is stain red pink. Ex. Safarain. 60sec

Question 2

Gram positive vs gram negative (thick or thin cell wall)

Answer 2

Gram positive has thick cell wall (peptidoglycan) covering plasma membrans (delicate)

Gram negative has thin cell wall (peptidoglycan)
Order outside in: outermembrane, thin peptidoglycan, plasma membrane (delicate)

Question 3

Function of decolorization (alcohol/acetone)

Answer 3

Dehydrate and denature agent

For gram positive; sucks water out of thick peptidoglycan layer and cell layer collapse, trapping the cv-i2 complex and color in the ce.
Thus gram positive is purple.

For gram negative, due to thin peptidoglycan wall, the dehydration and denaturing destroy the thin cell wall and the plasma membrane cant hold back the cv-i2 thus it comes out of cell and gram negative loses its primary stain

(It turn red bc it picked up the secondary stain safarain later)

Question 4

Iodine /mordant function

Answer 4

Form crystal violet iodine complex (cv-i2) which is bigger in size than crystal violet or iodine as such.

This seat the dye in the cell.

Question 5

Iodine /mordant function

Answer 5

Form crystal violet iodine complex (cv-i2) which is bigger in size than crystal violet or iodine as such.

This seat the dye in the cell.

Question 6

Advantage of gram staining

Disadvantage

Answer 6

Advantage:
Rapid and useful tool
Provide suggestive clues to what disease/bacteria
Valueble info to initiate course of antimicrobial treatment

Disadvantage:
often, disease causing bacteria do not have dkstinct stain characteristic (we can identify specific bacteria)

Not specific enough to diagnose

Question 6

Advantage of gram staining

Disadvantage

Answer 6

Advantage:
Rapid and useful tool
Provide suggestive clues to what disease/bacteria
Valueble info to initiate course of antimicrobial treatment

Disadvantage:
often, disease causing bacteria do not have dkstinct stain characteristic (we can identify specific bacteria)

Not specific enough to diagnose

Question 7

Examples of gram positive

Examples of gram negative

Answer 7

Positive:
staphyloccus aureus

Negative:
E coli