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We are trying to determine unknown microorganisms in intro to microbiology course. I first did gram stain and they were all cocci morphology, purple color and clumped together (actually I'm not so sure if clumped is right word, but they definitely were not in chains and I didn't see any isolated coccus, so if that's qualifies as clumped then they were clumped. So I have a gram+ here.

Next I did catalase test and got bubbles on slide; I put thick chunk of the unknown on slide and dropped 2-3 drops of ${H}_{2}{O}_2$; instant bubbling.

Next test.

So now I will test for coagulase but I'm uncertain what a positive or negative result will tell me about he organism and whether this is the terminal test (for ID-ing organism I mean)

My notes say that positive for coagulase indicates S. aureus. But does that mean that it is unnecessary to do the Mannitol test at that point then? Or is Mannitol used as a confirmation test?

Further, if unknown tests negative for coagulase, my notes say that if its also novobiocin sensitive (pos) then it is S. epidermidis.

But my same question then is, is it necessary to still do the mannitol test?

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    – James
    Commented Dec 2, 2016 at 7:29

1 Answer 1


At this point you have staph, you can use this flow chart (from here) to figure out what staph exactly.

If the test comes back as coagulase positive be very careful as Staph aureus is pathogenic.

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