unknown: s. aureus vs s. epidermidis

[thuydeebird]

I'm currently taking Microbiology and I am working on my unknown. I have narrowed down my unknown to S. Aureus and S. Epidermidis. I suspect that it is S. Aureus because my MSA plate turn yellow after incubation. However, when I did a coagulase test, it resulted in a gelatin like substance (not solid or liquid). Since it is not completely solid, I can't say that it is positive. This contradict my MSA plate because S. Aureus is coagulase positive. I'm not sure what test to believe. I have only done the coagulase test once and I have done the MSA test multiple time. I have picture of my MSA and TSA plate.

Is there anyone who can help me clear this up?

I also have picture of my MSA plate and TSA plate.

[JorgeLobo]

Repeat coagulase and use + and - controls.

[KIJRA]

Any clotting, even if it looks like gel, will be a positive result.

[JorgeLobo]

Repeat the test with controls. You should expect the appropriate reaction.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC187014/