Question

3. Name 3 biochemical tests that confirm that the bacteria isolated is Staphylococcus aureus.

4. Describe the test that you would use to determine whether the S. aureus that you identified above, is a MRSA.

5. Outline the procedure for Gram stain and negative stain. What would these stains determine?

Answer 1

3)

1. Gram staining : S. aureus is gram positive coci.
2. Growth on MSA : S. aureus can utilize Mannitol thus produce acid which results in yellow colored colonies
3. Growth on blood agar : it is beta-hemolysis positive, so there will be clear zone around colonies.

4)

If there is growth of S. aureus on media containing methicillin antibiotic, you can sa that the isolated S. aureus is methicillin resistance S. aureus (MRSA)

5)

Gram stain

1. primary staining by crystel violet (3-5 min.)
2. Washing
3. Grams iodine as mordant (30 seconds)
4. Washind with alcohol until blue color disappeares
5. Counter stain by safranin (5 min)

negative staining

• Spread acidic stain like nigrosin on smear with another slide, allow it to dry and observe under oil immersion.

​​​​​​​negative staining gives you information about morphology of bacteria and Gram staining give you information about morphology as well as gram character of the bacteria.