Lab: Gram staining, acid fast staining, spore staining

Question 1

Purple stain is gram ______

Answer 1

positive

Question 2

Pink stain is gram ______

Answer 2

negative

Question 3

gram + vs. gram - is separated based on

Answer 3

cell wall

Question 4

Describe gram + cell wall

Answer 4

thick peptidoglycan layers

Question 5

Describe gram - cell wall

Answer 5

thin peptidoglycan layers

Question 6

5 agents used in gram stain

Answer 6

1. crystal violet (primary stain)
2. gram’s iodine (complexing factor)
3. 95% ethanol (decolorizing agent)
4. safranin (secondary/counterstain
5. DI water (rinse)

Question 7

Which step separates gram + from gram - cells in the gram stain?

Answer 7

95% ethanol rinse; complex of crystal violet and gram’s iodine cannot escape thick pep. layer but can get out of thin one

Question 8

Acid fast staining

Answer 8

some bacteria have high mycolic acid conc. that resists decolorizing step giving a flase positive gram stain; Ziehl-Neelsen stain developed to deal with this, acid fast bacteria appear red against blue background

Question 9

spore staining

Answer 9

slide flooded with malachite green and placed over boiling water, heat causes formation of spore. flooded with safranin to counter stain. resulting image is a pink/red cell with green spore.