Anti-quorum Sensing Potential of Ethanolic Extracts of Aromatic Plants From Cyprus Flora

Quorum sensing (QS) is a form of intra- and inter-species communication system which is employed by bacteria to regulate their collective behavior in a cell population-dependent manner. QS has been implicated in the virulence of several pathogenic bacteria. This work aimed to investigate the anti-quorum sensing (anti-QS) potential of ethanolic extracts of eight aromatic plants of Cyprus namely, Origanum vulgare subsp. hirtum, Rosmarinus officinalis, Salvia officinalis, Lavendula spp., Calendula officinalis, Melissa officinalis, Sideritis cypria, and Aloysia citriodora. We initially assess the effects of the extracts on autoinducer 2 (AI-2) signaling activity, using Vibrio harveyi BB170 as a reported strain. We subsequently assess the effect of the ethanolic extracts on QS-related processes including biofilm formation and swarming and swimming motilities of Escherichia coli MG1655. Of the tested ethanolic extracts those of Origanum vulgare subsp. hirtum, Rosmarinus officinalis, and Salvia officinalis were the most potent AI-2 signaling inhibitors while the extracts from the other plants exhibited low to moderate inhibitory activity. The three ethanolic extracts also inhibited the biofilm formation (>60%) of E. coli MG1655, as well as its swimming and swarming motility in a concentration-dependent manner. These extracts may consider true anti-QS inhibitors because they disrupt QS-related activities of E. coli MG1655 without affecting bacterial growth. The results suggest that plants from the unexplored flora of Cyprus could serve as a source to identify novel anti-QS inhibitors to treat infectious diseases caused by pathogens resistant to antibiotics