narrowed down 1 of my unknowns help with other...

[chrissy0022]

Did enterotube on Gram - and it is E. coli.

Gram negative Stain- E. coli

Down to 2 possibilities for Gram + S. epidermis or M. luteus

Growth on MSA plate and no yellow so now waiting to do a VP test to figure out which of these bacterias it is

Gram positive

Any ideas?

[JorgeLobo]

Think I'd run an oxidase before Voges Proskauer is the test to seprrate Stpahylococcus spp. from Micrococcus spp. Staph can be neg on VP so only a + test is differentiating. I understand nNegative or weak oxidase with Microccocus spp. have been reported so here too a + test is most conclusive.

[chrissy0022]

I am following the flow chart we have been given and the next step is a VP test...

[JorgeLobo]

Thanks - not seen VP used so prominently in this context.

[canalon]

I imagine that in a case where students are given a number of unknown derived from a limited set that can be grown in the teaching lab, the chart that they are given is not one that is a realistic representation of how any given species would be identified in the wild. It is more like a dichotomous key (not really if you look at hemolysis here ) carefully crafted to separate the different candidates from one another in a minimum number of steps and at minimal cost. Usually this kind of lab is used to give students a feel for the different kind of tests that can be done and some practice with lab techniques rather than teach them a rational diagnosis tool that would be used in medical microbiology.

[JorgeLobo]

Good point

[chrissy0022]

My second Unknown should have been S. Epidermis but I had a negative result on My VP Test....leading me to conclude that it was M. Luteus...
and ideas why that would happen?

[JorgeLobo]

Why what would happen?

[chrissy0022]

Why I got a negative result on my VP test

[JorgeLobo]

"Should have been S. epidermidis" -why do you say this? Is this what your instructor said?

[chrissy0022]

yes that is what she said that is was S. epidermis...

[JorgeLobo]

Suppose youncould defend that this is a nonroutine test in this context. You might run it again with controls.