**6.1 Pigment inhibition assays**

Formation of violacein, a purple pigment in the reporter strain Chromobacterium violaceum is controlled by quorum sensing [132]. Quantifying the inhibition of violacein synthesis, by paper disc diffusion as well as flask incubation assay is thus used as a method for screening AQS activity of a given compound. Presence of a zone of inhibition in paper disk diffusion plates and significant reduction in violacein content in flasks, are considered as positive results. This method was efficiently used to test the AQS activity of Vanilla extract [133], pigments extracted from Auricularia auricular [134], essential oils [135], fruit extracts of Passiflora edulis [136], and a few compounds isolated from plant endophytic bacteria [137]. Similarly, inhibition of pigment production in Serratia marcescens is also a coherent test to determine the quorum quenching activity of a compound [138].
