Investigating Some Culinary Herbs as Potential Anti Quorum Sensing Agents in the Environment

Abstract

Bacteria communicate via quorum-sensing (QS) before exhibiting detrimental or beneficial effects to man and the environment. This QS is indispensable for biofilm formation, which results to medical and environmental consequences. Interrupting QS using culinary herbs may address membrane biofouling and prevent biofilm-related diseases, while reducing the risks of bacterial resistance. In this study, Leaves of Cymbopogon citratus, Rosmarinus officinalis and Ocimum basilicum were extracted in organic solvents of varying polarity. Anti-quorum sensing (AQS) activities of the extracts were investigated at both qualitative and quantitative levels against a locally isolated Chromobacterium violaceum, using solid and liquid media bioassays. Plant extracts with peak AQS activities were characterized using chromatographic techniques. The extracts were fractionated and the promising fractions were re-isolated and delineated by Fourier transform infrared spectroscopy (FTIR) as well as Gas chromatography-mass spectrometry (GC-MS) profiling. Solvents of higher polarity (aqueous and methanol) gave a bumper yield (5.96%, 4.77% and 4.67%) of the recovered extracts. Only two species (R. officinalis and O. basilicum) exhibited a noteworthy AQS activity in the agar well diffusion assay. However, all the extracts inhibited violacein production (3.70–60.49%) in the quantitative AQS bioassay. The FTIR and GC-MS analyses revealed the presence of alcohols and p-Cymene as the commonest functional group and most abundant compound respectively in the most active fraction (R2) of R. officinalis. The aqueous and methanol extracts (especially of R. officinalis) in both crude and isolated forms appreciably inhibited bacterial biofilms and indicated good features of AQS activities.