Gram Staining

Question 1

gram stain/differential stain

what is the differential stage in the procedure?

Answer 1

allows you to determine gram-positive bacteria or gram-negative bacteria

the acetone

Question 2

primary stain

Answer 2

crystal violet, all bacteria are stained purple by this method

Question 3

mordant

Answer 3

the iodine
combines with the crystal violet in the cell wall to form crystal-violet iodine complex
it allows the crystal violet to adhere to the cell wall and prevent it from washing away

Question 4

counterstain

Answer 4

safrainin, stains the decolorized bacteria red

Question 5

decolorizing agent

Answer 5

ethanol or ethanol aceteone used to wash out the primary stain of some bacteria while others are unaffected

Question 6

why is a gram stain best performed on a young culture (less than 24 hours old) ?

Answer 6

because older cultures give you a false negative

Question 7

what are the steps in gram-negative staining

Answer 7

1. cover the smear with crystal violet
2. wash off crystal violet with water
3. cover smear with grams iodine (mordant)
4. wash the smear with water
5. decolorize with ethanol
6. wash off the ethanol
7. cover smear with safranin
8. wash smear with water
9. blot it dry

Question 8

gram negative cell structures?

Answer 8

plasma membrae->thin peptidoglycan layer->outermebrane

Question 9

gram-positive cell structure

Answer 9

plasma membrane->thick peptidoglycan layer

Question 10

why is gram-staining done before prescribing antibiotics

Answer 10

some antibiotics works gram positive and some work on gram negative

Question 11

why might a bacteria that is gram postive stain gram negative

Answer 11

too thin of a smear or over colorization

also indicates older colony which gives a false gram-negative

Question 12

why might bacteria that is gram negative stain gram positive ?

Answer 12

too thick of smear makes it hard to wash off with acetone which will lead to under colorization