Antibiofilm activity of Equisetum hyemale: interference with quorum sensing

Introduction: Biofilm formation results from successive stages of adhesion and coaggregation/auto aggregation, bacterial motility, and quorum sensing (QS), mediated by chemical signals that determine group microbial behaviour. Thus, it is important to look for alternatives that are capable of interfering with these parameters and, consequently, inhibit the formation of biofilms. Plants are a rich source of research, as they produce secondary metabolites that have important biological activities. In this study, we aimed to evaluate the antimicrobial, antibiofilm, and antiquorum sensing activities of a crude extract, fractions, and major substances produced by Equisetum hyemale against P.Pseudomonas aeruginosa.Methods and results: The extracts and the fractions inhibited the bacterial growth of P. aeruginosa PA01 (MIC ranging from 26.2 to 13.1 mu g/mL), as did the major substances (minimal inhibitory concentration (MIC) between 0.75 and 0.37 mu g/mL). Using the biofilm inhibition technique on polystyrene plates, we observed that the crude extract and fractions were able to inhibit biofilm formation by 29-64%, while the major substances inhibited biofilm formation by 67-79%. Atomic force microscopy allowed us to visualise the decrease in microbial mass. Colony counting also showed that there was a significant difference in the colony counts, in relation to the positive control. Moreover, all extracts and compounds were shown to influence motility (swimming, swarming, and twitching). To evaluate QS inhibition, we assessed violacein, a mediator of QS induced by the CviI autoinducer synthase; the plant extract and the major compounds were able to significantly reduce the production of violacein at subinhibitory concentrations.Conclusions: In view of this, we have shown that this plant has relevant antibiofilm activity and interferes with biofilm formation factors and QS.