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

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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

Postby chrissy0022 » Sat Apr 21, 2012 12:47 pm

Did enterotube on Gram - and it is E. coli.
gram negative 3.jpg
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 cocci.jpg
Gram positive


Any ideas?
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Re: narrowed down 1 of my unknowns help with other...

Postby JorgeLobo » Mon Apr 23, 2012 9:50 pm

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

Postby chrissy0022 » Tue Apr 24, 2012 12:46 am

I am following the flow chart we have been given and the next step is a VP test...
Untitled1.png
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Postby JorgeLobo » Tue Apr 24, 2012 1:57 am

Thanks - not seen VP used so prominently in this context.
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Postby canalon » Tue Apr 24, 2012 10:42 am

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.
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Postby JorgeLobo » Tue Apr 24, 2012 11:02 am

Good point
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Re: narrowed down 1 of my unknowns help with other...

Postby chrissy0022 » Thu Apr 26, 2012 4:43 am

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?
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Re: narrowed down 1 of my unknowns help with other...

Postby JorgeLobo » Thu Apr 26, 2012 8:30 pm

Why what would happen?
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Re: narrowed down 1 of my unknowns help with other...

Postby chrissy0022 » Fri Apr 27, 2012 2:24 am

Why I got a negative result on my VP test
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Re: narrowed down 1 of my unknowns help with other...

Postby JorgeLobo » Fri Apr 27, 2012 10:16 am

"Should have been S. epidermidis" -why do you say this? Is this what your instructor said?
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Re: narrowed down 1 of my unknowns help with other...

Postby chrissy0022 » Sat Apr 28, 2012 2:46 am

yes that is what she said that is was S. epidermis...
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Re: narrowed down 1 of my unknowns help with other...

Postby JorgeLobo » Sun Apr 29, 2012 12:09 pm

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