[jess17]

Hello! My professor gave each of us an "unknown" bacteria that we have to identify by following certain staining methods. Does anyone know how to tell the difference between staph aureus and staph epidermidis? I know that what I have is between those two, but under the microscope they look the same. The next thing I would need to do to figure it out would be to see if it has yellow colonies or white colonies....but I'm not sure how to figure that out since we used Gram staining...and the colonies were purple from that. If anyone has any idea I would GREATLY appreciate it. Thank you so much.

[Asherah]

Well if you are sure you can tell the difference from colony color all you should have to do is transfer your original sample to a fresh petri dish with regular agar nutrient. Be sure to transfer the pure culture (no contamination) and then heat or cool at optimal growth temperature for the designated time frame. (I'm not sure how much time you have to do this however, so that would depend on when this is due.)

[Slimlady727]

You only observe colonies on plates. So you would have to innoculate a plate and then see what color they are after there is growth.


But I can check my notes and get back to you. PM me with questions.

[♪♫ in my ♥]

The distinguishing features between S. aureus and S. epidermidis are:

1) S. aureus can ferment manitol while S. epidermidis cannot

2) S. aureus is pigmented a golden yellow color (hence, the name) while S. epidermidis is no.

Streak on mannitol salt agar and see what you get.



The fermentation of mannitol lowers the pH and the phenol red indicator turns yellow.

[jess17]

thank you all so much