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I recently performed a lab to test different concentrations (20-99%) of isopropyl alcohol and its inhibition of E. coli growth. My control was an antibacterial disk, and what I did was I dabbed the disk in each concentration and put it on the agar with the E. coli. I dabbed it enough so it wasn't soaking wet but it still had some liquid.

Unfortunately, I had no results at all from the alcohol-soaked disked, but I know the experiment should work because the antibacterial disks for all Petri dishes worked.

I don't know why the alcohol did not work at all though, especially since it is proven to be effective as a disinfectant at least for E. coli.

If anyone has a link with this exact lab being tested, or something similar (isopropyl alcohol and effect on zone of inhibition in bacteria labs) that would be amazing. Concentrations 20,30,40,50,60,70,80,99% -Disk diffusion, I put the bacteria by streaking across the quadrants -I dipped the disks until it was soaked then dabbed enough to make sure it wasn't dripping -Negative control:sterile disk In the middle, positive control: antibacterial disk on quadrant A -I was going to measure zone of inhibition but there was none produced for all 12 plates except for quadrant A containing the antibacterial disk.

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    $\begingroup$ At 70 - 80% EtOH should work for sure. Can you give us details of the concentrations EtOH used, the kind of plates/medium used, the method of plating (colonies or smooth surface of evenly distributed growth), the contact time of EtOH, the way EtOH was removed (evaporation/drying/etc), the strain of E.coli, and so forth, the study design (what was your negative and positive control), and last but definitely not least, the outcome measure used to determine the #cells left after treatment? $\endgroup$ – AliceD Dec 11 '19 at 21:49
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    $\begingroup$ Just a thought: isopropanol is quite volatile and might just evaporate from the disk rather then diffuse into the agar, especially at 37C. I'm not sure the disk diffusion method is appropriate for testing microbial sensitivity of volatile liquids. $\endgroup$ – canadianer Dec 11 '19 at 23:06
  • $\begingroup$ @AliceD This is all I know: -Concentrations 20,30,40,50,60,70,80,99% -Disk diffusion, I put the bacteria by streaking across the quadrants -I dipped the disks until it was soaked then dabbed enough to make sure it wasn't dripping -Negative control:sterile disk In the middle, positive control: antibacterial disk on quadrant A -I was going to measure zone of inhibition but there was none produced for all 12 plates except for quadrant A containing the antibacterial disk. Thank you for your fast reply, I didn't expect there to be an answer so I'm sorry this is late $\endgroup$ – starwberry501 Dec 20 '19 at 5:19
  • $\begingroup$ @canadianer I am thinking the same but do you know any references I can cite? I have to evaluate my procedure but I have no way to cite any of my assumptions :( $\endgroup$ – starwberry501 Dec 20 '19 at 5:21

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