Anti-Quorum Sensing Activity of 12 Essential Oils on chromobacterium violaceum and Specific Action of cis-cis-p-Menthenolide from Corsican Mentha suaveolens ssp. Insularis

Quorum sensing (QS) is a bacterial communication mechanism used to express various survival or virulence traits leading to enhanced resistance. <i>Chromobacterium violaceum</i> is a commonly used strain that highlights anti-QS action of bioactive substances. Here, we wanted to see if 12 selected essential oils (EO) could exert anti-QS activity. We measured the sublethal minimal QS inhibitory concentration (MQSIC) by assessing violacein production of <i>C. violaceum</i> along with bacterial growth. To confirm the QS disruption, we also proceed to surface bacterial observations using scanning electron microscopy (SEM). We showed that <i>cis-cis-p-</i>menthenolide extracted and isolated from a plant endemic to occidental Mediterranean Sea islands, <i>Mentha suaveolens</i> ssp. <i>insularis</i>, acts as an inhibitor of violacein production and biofilm formation. Measured MQSIC was much lower than the minimal inhibitory concentration (MIC): 0.10 mg·mL^-1 vs. 3.00 mg·mL^-1. Moreover, disturbance of QS-related traits was confirmed by the degradation of <i>C. violaceum</i> biofilm matrix. There is a clear structure⁻activity relationship between <i>cis-cis-p-</i>menthenolide and anti-QS activity. Indeed, its isomer molecule (mintlactone) exerts a poor anti-QS action. These results indicate that inhibition of violacein production and biofilm formation by <i>cis-cis-p-</i>menthenolide might be related to a disruption in the QS mechanism.