Staining (DR)

Question 1

Process of staining a sample

Answer 1

1) place the sample onto the slide and allow to dry or fix it via a pass through a flame
2)stain the sample using a +vely or -vely charged dye, this applies contrast

Question 2

Positively charged dyes

Answer 2

Methylene Blue
Crystal Violet

These are attracted to the -ve areas of the cell like the cytoplasm and nucleus

Question 3

negatively charged dyes

Answer 3

Nigrosin
Congo Red

These are attracted to the +ve areas of the cell like the outside of the cell

Question 4

Gram Negative Bacteria
-ve

Answer 4

-have a thin peptidoglycan layer sandwiched between 2 membranes
-has an outer membrane made of LPS proteins
-stains PINK as there is not enough peptidoglycan to retain the purple Crystal violet dye.
-Less susceptible to penicillin and more resistant to antibiotics due to the protective outer membrane.

Question 5

Gram Positive Bacteria
+ve

Answer 5

-Thick peptidoglycan layer
-NO outer membrane
-stains PURPLE as the thick peptidoglycan retains the crystal violet dye
-More susceptible to penicillin, which targets the cell wall (has no extra outer membrane like Gram -ve)
-less prone to resistance compared to Gram -ve bacteria

Question 6

DEFINITION
Differential staining

Answer 6

allows you to distinguish 2 types of organisms
-used to distinguish gram -ve and gram +ve bacteria

Question 7

Differential staining of bacteria (gram staining)

Answer 7

Step 1) fix bacteria with a quick pass through flame

Step 2) Crystal Violet dye

Step 3) Iodine this fixes Crystal violet, Gram +ve bacteria
retain the purple dye in their thicker peptidoglycan layer

Step 4) Wash away dye with alcohol (Gram -ve bacteria lose the purple dye due to their too thin peptidoglycan layer)

Step 5) Safranin stains Gram -ve bacteria
PINK (It stains all bacteria but the -ve are MORE clearly pink)