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
  • $\begingroup$ It is not uncommon for bacteria to stop producing pigments when cultivated on artificial media in the lab. $\endgroup$
    – user37894
    Mar 28 '18 at 16:47
  • $\begingroup$ 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. $\endgroup$ Dec 19 '19 at 8:59

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