1, 2

Question 1

Crystal violet

Answer 1

binds to peptidoglycan in the cell wall

Question 2

Lugol’s iodine

Answer 2

fixes the crystal violet to the peptidoglycan

Question 3

Carbol fuchsin

Answer 3

red stain applied so that gram negative cells can be visualised

Question 4

Gram positive

Answer 4

blue/purple

Question 5

gram negative

Answer 5

red/pink

Question 6

first step of gram stain

Answer 6

crystal violet, 30 seconds, then rinse

Question 7

second step of gram stain

Answer 7

lugol’s iodine, 30 seconds, then rinse

Question 8

third step gram stain

Answer 8

alcohol or acetone to decolonise, then rinse

Question 9

forth step gram stain

Answer 9

carbol fuchsin, 30 seconds then rinse

Question 10

heat fixing

Answer 10

• Slide is passed briefly through the flame of a bunsen burner
  
  • Cant get too hot or the bacteria will alter their shape
  • Ensures specimen doesn’t wash off during staining

Question 11

staph, strep and enterococcus are all

Answer 11

gram positive cocci that are facultative anaerobes - meaning they grow in air and anaerobically

Question 12

staph morphology

Answer 12

round, arranges in grape like clusters

Question 13

strep morphology

Answer 13

round arranged in chains

Question 14

enterococcus morphology

Answer 14

short chains or pairs

Question 15

the catalase test differentiates between

Answer 15

staph vs (strep/entero)

Question 16

how to staph react to the catalase test

Answer 16

• Staphylococci possess the enzyme catalase which will convert hydrogen peroxide to water and oxygen
  
  • 2H2O2 -> 2H2O + O2

Question 17

catalase test process

Answer 17

○ A portion of the bacterial colony being tested is mixed with a few drops of hydrogen peroxide on a glass slide. A positive result is indicated by the appearance of oxygen bubbles

Question 18

positive catalyse test

Answer 18

staph

Question 19

negative catalase test

Answer 19

strep or entero