4
$\begingroup$

For my science fair project, I did an experiment on how paracetamol and ibuprofen affected the growth of bacteria. By day 5, however, parts of the paracetamol blackened (image below). I am wondering if E. Coli can metabolize paracetamol and if so, what operon in the K-12 genome is responsible for this.

image of petri dish

EDIT: I realized it may be metabolizing other ingredients in the medicine I used. I am including a list of the ingredients in the medicine I used.

Acetaminophen 160 mg in each 5 mL (duh)

Other ingredients (33.015873 mL):

  • Anhydrous citric acid
  • FD&C red no. 40
  • glycerin
  • high fructose corn syrup
  • microcrystalline cellulose and carboxymethylcellulose sodium
  • purified water
  • sodium benzoate
  • sorbitol solution
  • sucralose
  • xanthan gum

I thought it might be the fructose, but is the byproduct really black? Still confused...

$\endgroup$
  • $\begingroup$ I thin, you are using blood agar plates, isn't it? In this case, it could also be the heme which can cause the black colour. $\endgroup$ – SeRe Nov 20 '17 at 10:34
  • $\begingroup$ No, the medicine I used colored the agar red. I used regular agar. $\endgroup$ – JavaScriptCoder Nov 20 '17 at 15:00
  • $\begingroup$ Is it possible the dye changes colour as the pH decreases? $\endgroup$ – canadianer Nov 20 '17 at 20:02
1
$\begingroup$

Sorry that my answer is not a real answer, but this would be a good starting point for some more science.

Several of the questions you might ask and could answer (with some more experiments):

  • Does this happen in plates without E.coli?
  • You have a contamination on the right side, perhaps also on the black part. Could this be the culprit? Only half the plate is black, the rest is (still?) red.
  • You used a paracetamol tablet with red dye and a lot of sweeteners, does the same thing happen if you use one without the red dye? A dye would be a likely source, because it already contains an absorbing moiety. It only needs to be slightly modified to absorb different wavelengths.
  • What kind of agar are you using exactly? There are many kinds, often selecting for certain types of micro-organisms, with indicators for pH or other colored markers to detect and identify strains.

For your metabolic question you can take a look at https://ecocyc.org/ where you can find a database with all known metabolic pathways for E.coli K12. Unfortunately I couldn't find anything for paracetamol (or synonyms) but you could try to see if it produces a colored product for any of the additives.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.