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Need help with my unknown organism?? Confusing test results

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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Need help with my unknown organism?? Confusing test results

Postby SweetSarah » Sun Feb 26, 2012 7:22 am

I just got my TSI test result for my unknown today in lab but my results really confused me since it didn't look like any of the examples in my lab book nor could I find anything like this online. I'm not sure if I should redo it. My TSI slant has a red (alkaline) butt but has black on top, which I'm assuming is for H2S (hydrogen sulfide) production. But what confuses me is that there's no acid production in it at all, so what I though my organims was all this time (I thought it was Proteus or Salmonella since I had black coloration on all my agar plates and those both produce H2S but I guess it's not afterall).
--So, then could it be a Pseudomonas?
My test results seem to match that one actually since my organism came out glucose negative and lactose negative. I'm waiting for more test results to make sure.
--Though, I don't know what type of Pseudomonas would produce H2s?
--do u know by any type of Pseudomonas that can by any chance??

I'm really hoping I didn't do the tests wrong. I redid some just in case. Though am worried I may get the same result. It's like no matter what test I do, no matter what all the media I use come out with this black coloration and I don't know if it could be due to hydrogen sulfide (H2S) anymore since mine is glucose negative (I did several tests all came out negative and no color change at all), so that's why now I cancelled out the H2S-producing organisms on my list like Proteus. So basically what I'm trying to say is that my test results are confusing me ,especially since I got black coloration on everything (which I assume is due to H2S) but since my other test results seem to go with Pseudomonas for the most part.

Here are my test results by the way if anyone wants to see and help me out more. That's okay if not. My main questions were above but this would help out more by the way, thanks in advance:
TSI: Alkaline butt, H2S (black) slant (on top), not yellow or acidic
(in my book there are examples of TSI results but the closest has alkaline slant with H2S, none like this...)

Nitrate: Positive? (I am not sure of this one but after adding zinc , no red color formed and it was cloudy whitish-clear color tube)

Urease: negative (this helped me rule out Proteus)

Glucose and Lactose fermentation: both negative

So, My organism is a Nonfermenter

Citrate: Positive? (turned slightly blue but am not sure if that's good enough to say it's positve since still some green)

So with all these test results some seem kind of conflicting. COuld I have Pseudomonas or is it something else. I believe it may be but the H2S production confuses me as from what I read Pseudomonas I don't think would do that? does it?? :/
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Postby SweetSarah » Sun Feb 26, 2012 7:49 am

**I forgot to mention but it's GRAM NEGATIVE, in rods/bacilli. I believe it's Enterobacteriaceae by the way. (under microscope it looked like tiny, thin pink rods)
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Re: Need help with my unknown organism?? Confusing test results

Postby JorgeLobo » Sun Feb 26, 2012 2:35 pm


Please consider that not all criteria ( as test results) are equal. Start from the general and go to the specifics - for example it's very unlikely to be an enteric (Enterobacteriaceae) if it doesn't ferment glucose and, as you correctly observed, that should have tuled out Proteus more so than the hydrogen sulfide or urease result.

There is at least one pseudomonad that produces hydrogen sulfide as indcate inn TSI - Shewanella (formerly Pseudomonas) putrefaciens.
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