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Assistance in identifying a bacterium


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In my Systematic Bacteriology lab, my partner and I have managed to isolate a very interesting (and frustrating) bacterium from a local pond/fountain and we are absolutely baffled as to what exactly it is. Because while it does seem to grow on R2A and TSA agar, it is proving incredibly difficult to grow in anything else; including the common identification tests for Gram-negative rods. What we do know is that its colonies are a reddish colour on R2A and TSA and they are very, VERY sticky; whenever we try to get a loopful of them we end up having to try a half-dozen times because we end up peeling off all the growth in a small area whenever we try. I can only assume that it's a capsule that is responsible, but we still do not know what it could be.


We thought maybe it could be Serratia marcescens, since it's well known to form red, and I think sticky, colonies. But I'm not sure. If anyone has any suggestions as to what genus this might be I would be very grateful, because this is really starting to drive my partner and I up the wall.


What we do know:


-Catalase positive

-Gram-negative rods

-Isolated from an outdoor fountain/pond

-Tween 80 negative

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Don't try to force fit identification based on apparently limited knowledge - Serratia is not known typically to produce colonies of the type you describe and other bacteria also produce red pigmentation (including production of prodigiosin). Map out a scheme of identification and test accordingly, as I'm sure is the idea of the course. Ensuring a pure culture, initial determinations would include determining the isolate's cellular morphology, response to oxygen (as an aerobe, facultative, microaerophile etc.), motility. Pigmentation and colony consistency are still a very good criteria for narrowing the potential candidates - might look at Rugamonas (it's pigmentation is often slow to develop) but do go through the process.

Edited by JorgeLobo
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