Abstract
The discovery of quorum sensing in Proteobacteria and its function in regulating virulence determinants makes it an attractive alternative towards attenuation of bacterial pathogens. In this study, crude extracts of Phyllanthus amarus Schumach. & Thonn, a traditional Chinese herb, were screened for their anti-quorum sensing properties through a series of bioassays. Only the methanolic extract of P. amarus exhibited anti-quorum sensing activity, whereby it interrupted the ability of Chromobacterium violaceum CVO26 to response towards exogenously supplied N-hexanoylhomoserine lactone and the extract reduced bioluminescence in E. coli [pSB401] and E. coli [pSB1075]. In addition to this, methanolic extract of P. amarus significantly inhibited selected quorum sensing-regulated virulence determinants of Pseudomonas aeruginosa PA01. Increasing concentrations of the methanolic extracts of P. amarus reduced swarming motility, pyocyanin production and P. aeruginosa PA01 lecA∷lux expression. Our data suggest that P. amarus could be useful for attenuating pathogens and hence, more local traditional herbs should be screened for its anti-quorum sensing properties as their active compounds may serve as promising anti-pathogenic drugs.
Highlights
The emergence of more multidrug resistant pathogens at an alarming rate is a major concern to the public health care and policy makers in the medical industry
We report for the first time the anti-Quorum sensing (QS) properties of P. amarus and its methanolic crude extract is shown to inhibit selected virulence factors of P. aeruginosa PAO1
A bacterial growth curve (OD600) was determined over a period of 24 h to rule out any antibacterial properties of the methanolic extracts of P. amarus that may inhibit growth of C. violaceum CV026 and
Summary
The emergence of more multidrug resistant pathogens at an alarming rate is a major concern to the public health care and policy makers in the medical industry. Quorum sensing (QS) is a cell-cell signaling system whereby bacteria produce signalling molecules, termed autoinducers, that coordinate the production of cell density-dependent regulatory factors as well as the expression of virulence factors in pathogens [1,2]. One of the best characterised QS models is Pseudomonas aeruginosa, which consists of two QS systems namely lasI/R and rhl/R, which function in a hierarchal way, and regulate expression of several virulence genes [3,4,5]. Anti-QS compounds may target the QS-systems either by disrupting the AHL synthase, the signal molecule itself, or AHL target receptors [10]. We report for the first time the anti-QS properties of P. amarus and its methanolic crude extract is shown to inhibit selected virulence factors of P. aeruginosa PAO1
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