Hi Roman,

Remember that inhibition or otherwise is a function of concentration. Low diffused concentration was responsible for the reduction in the inhibition of the bacteria in second zone. At the same time, like you also have said, violacein expression wasn't deep in that same zone, because of low bacterial density. The higher the bacterial population the easier the possibility to form quorum. This is why invasion often precedes quorum sensing, though more rapid invasion would be experienced after successful quorum formations

In my opinion this is caused by the inhibition of quorum sensing. I also had made some similar experiments few years ago. You can try to make some others screening studies e.g. add this compound to agar plates, during prepatation of them, and then when the agar plates will be solid seed bacteria on them. If this compond have a quorum qenching activity, bacteria growing on plates will be white/ translucent.

I performed a similar experiment but in a different way. It consisted on mixturing melted agar with bacterial culture. Once dried, I did wells in it and put 40 ul of extract. I think that Pawel's suggestion sounds great. I wish I would've had enough extract to carry out that, too. I recommend you to try other screenings like testing C. violaceum growth in broth with your compound to realize how bacterium behaves in compound's presence. Also, you can do the extraction and quantification of violacein to see if there is a decrease of the pigment when grown with the compound. In my case, the results from these last two assays were different to the agar diffusion results. From my experience, I consider that one assay is not enough to conclude if a compound inhibits QS. It is necessary to include bacterial growth assays with the compound. Also, I am not sure but all that green-yellow zone remainds me when Pseudomonas aeruginosa used to "invade" my assays, specially the most external halo that looks like swarming motility.

You cannot say for certain simply by conducting AST. To have a confirmatory result do MIC, MBC test. It will give you a definite result (which will clear all doubt regarding this matter).

I am in consensus with Anthony Ayodeji Adegoke. However, in my experience studies with CV is not enough to conform quorum sensing inhibitory property. In our lab we have identified compounds with significant anti-QS property who exhibited no reduction in violacein production and vice versa.

That is a nice shot. Inner ring with no bacterial cell shows anti-microbial activity while the outer one with no violacein but bacterial growth highlights anti-QS. Good luck!

I think this paper will be useful for you,

https://www.cell.com/biophysj/fulltext/S0006-3495(17)30105-4

I agree with Milad, clear differentiation of Antibiotic and Anti-QS activity I hope.

Growth curve and violacein quantification are must to confirm this further.

The following article may be helpful.

https://www.mdpi.com/1660-3397/11/1/253/htm

Best wishes !

Hi Roman,

I need your help , i am working on inhibition of quorum sensing in Chromobacterium violaceum MTCC 2656culture. but my culture doesnt produce the purple pigment which i see in your plate and read in articles. my question is addition of commercially available long chain AHL will induce the pigment production ?how can i go about it