In the analysis of an unknown bacterial broth I observed a gram negative rod genus. Upon plating I observed small, dark purple and convex colonies; corresponding presumably to Chromobactierum. After then replating the purple colonies I then observed white fillamentous colonies that were gram negative and was subsequently able to make an identification that suggested the organism was either of genus aeromonas, vibrio or Chromobactierum. I found an article showing that Chromobactierum colonies dont have to be purple and can have a range of morphologies (see link). My question is: upon replating, can the morphology of the two colonies change so drastically?( assuming I had two different strains of Chromobacterium present)


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    $\begingroup$ This different Gram reaction suggests you have a contaminant. $\endgroup$ – canadianer Mar 10 '18 at 16:30
  • $\begingroup$ Sorry error on my part. The purple bacteria observed on the first plate were gram negative $\endgroup$ – THN Mar 10 '18 at 21:06
  • $\begingroup$ Did you PCR the 16S?? Most phyla are Gram negative and several skin flora bacteria are negative and unpigmented —yes, there will be many bright yellow staphs (+) and red Serratia marcensis (-), but not all. So I agree with the contamination hypothesis. $\endgroup$ – Matteo Ferla Dec 19 '19 at 8:59

It is not uncommon for bacteria to stop producing pigments when cultivated on artificial media in the lab.

  • $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review $\endgroup$ – fileunderwater Mar 28 '18 at 17:40
  • $\begingroup$ My answer is neither a critique nor a request for clarification from the author of the question. My answer is an answer. $\endgroup$ – user37894 Mar 29 '18 at 15:10
  • $\begingroup$ Sorry, the specific comment is autogenerated by the review queue. My point is that it has the character of a brief suggestion or comment, without explanation, background or references. Therefore, I think it is most suitable as a comment. $\endgroup$ – fileunderwater Mar 29 '18 at 15:25

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