Carvone - a quorum sensing inhibitor blocks biofilm formation in Chromobacterium violaceum

Carvone is a natural monoterpenoid and in this study it was tested for its role in attenuating quorum sensing (QS) controlled biofilm formation in Chromobacterium violaceum. It showed significant QS inhibition in terms of reduction in violacein at a concentration range of 60 to 70 µg/mL against C. violaceum ATCC 12472. At the same concentration, carvone also inhibited biofilm formation by more than 80%. The biofilm morphology of C. violaceum is unique with a well organised pattern of cell arrangement in a tight matrix. The same was evident in Scanning electron microscopy, however, carvone treatment not only showed reduction in biofilm density but also disruption of biofilm matrix. Interruption of biofilm formation was attributed to reduction in the exopolysaccharide production and swarming motility. Molecular investigations (RT-PCR) showed that the important genes involved in biofilm regulation such as pilS, pilR, pilB and pilT were downregulated significantly in the treatment groups.