Abstract
The quorum sensing (QS) system has been used by many opportunistic pathogenic bacteria to coordinate their virulence determinants in relation to cell-population density. As antibiotic-resistant bacteria are on the rise, interference with QS has been regarded as a novel way to control bacterial infections. As such, many plant-based natural products have been widely explored for their therapeutic roles. These natural products may contain anti-QS compounds that could block QS signals generation or transmission to combat QS pathogens. In this study, we report the anti-QS activities of four different Chinese herbal plant extracts: Poria cum Radix pini, Angelica dahurica, Rhizoma cibotii and Schizonepeta tenuifolia, on Pseudomonas aeruginosa PAO1. All the plants extracted using hexane, chloroform and methanol were tested and found to impair swarming motility and pyocyanin production in P. aeruginosa PAO1, particularly by Poria cum Radix pini. In addition, all the plant extracts also inhibited violacein production in C. violaceum CV026 up to 50% while bioluminescence activities were reduced in lux-based E. coli biosensors, pSB401 and pSB1075, up to about 57%. These anti-QS properties of the four medicinal plants are the first documentation that demonstrates a potential approach to attenuate pathogens’ virulence determinants.
Highlights
Pseudomonas aeruginosa PAO1 is a Gram-negative bacterium that is well known to cause various diseases, such as respiratory system infections, urinary tract infections, dermatitis, soft tissue infections, as well as bone and joints infections [1]
The effect of R. pini, A. dahurica and R. cibotii on pyocyanin production suggests the presence of compounds which act as inhibitors of rhl system in the plant extracts [33]
Results showed that all the plant extracts, R. pini, were able to reduce swarming in P. aeruginosa PAO1 (Figure 5)
Summary
Pseudomonas aeruginosa PAO1 is a Gram-negative bacterium that is well known to cause various diseases, such as respiratory system infections, urinary tract infections, dermatitis, soft tissue infections, as well as bone and joints infections [1]. Previous studies have shown that P. aeruginosa has the ability to produce and secrete various virulence factors such as extracellular enzymes, haemolysins, toxins, secondary metabolites, pili and alginate [8]. These virulence factors are believed to be the main contributors for both acute and chronic infections in immunocompromised patients as they can generally damage both tissues and organs as well as interfere with the human immune system defense mechanism [9]. Research have shown that plant-derived sources such as malabaricone C (from Myristica cinnamomea) [18], Melicope lunu-ankenda [19] and Phyllanthus amarus [20] could inhibit QS responses in bacteria without affecting their growth. The effect of the plant extracts on bioluminescence production by Escherichia coli [pSB401] and E. coli [pSB1075] were assessed
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