Abstract
The increasing incidence of multidrug-resistant pathogens has stimulated the search for novel anti-virulence compounds. Although many phytochemicals show promising antimicrobial activity, their power lies in their anti-virulence properties. Thus the quorum sensing (QS) inhibitory activity of four crude Kigelia africana fruit extracts was assessed qualitatively and quantitatively using the Chromobacterium violaceum and Agrobacterium tumefaciens biosensor systems. Inhibition of QS-controlled violacein production in C. violaceum was assayed using the qualitative agar diffusion assay as well as by quantifying violacein inhibition using K. africana extracts ranging from 0.31–8.2 mg/mL. Qualitative modulation of QS activity was investigated using the agar diffusion double ring assay. All four extracts showed varying levels of anti-QS activity with zones of violacein inhibition ranging from 9–10 mm. The effect on violacein inhibition was significant in the following order: hexane > dichloromethane > ethyl acetate > methanol. Inhibition was concentration-dependent, with the ≥90% inhibition being obtained with ≥1.3 mg/mL of the hexane extract. Both LuxI and LuxR activity were affected by crude extracts suggesting that the phytochemicals target both QS signal and receptor. K. africana extracts with their anti-QS activity, have the potential to be novel therapeutic agents, which might be important in reducing virulence and pathogenicity of drug-resistant bacteria in vivo.
Highlights
Since plants live in environments with high microbial loads, it is not surprising that they have developed innovative protective mechanisms against bacterial infections [1]
Various species of marine algae and higher plants, including traditional medicinal plants and dietary fruits, herbs, and spices have been shown to interfere with bacterial quorum sensing (QS) and attenuate bacterial pathogenicity [3,6,7,9,18]
K. africana fruit extract phytochemical-based anti-virulence therapy strategy is that it would circumvent the problem of resistance, associated with the use of conventional antimicrobial agents, since it interferes with the expression of QS-associated virulence traits rather than being bactericidal
Summary
Since plants live in environments with high microbial loads, it is not surprising that they have developed innovative protective mechanisms against bacterial infections [1]. Many phytochemicals are not highly effective as antimicrobial agents, instead they possess anti-pathogenic or anti-virulence properties, which are neither bactericidal nor bacteriostatic and do not cause the development of resistant bacteria Instead these compounds attenuate the expression of genes responsible for pathogenesis and virulence by interfering with quorum sensing (QS) and other related properties [3]. Phytochemicals often have multiple therapeutic effects and one of their mechanisms of action might be QS inhibition or modulation, whereby they attenuate the expression of virulence genes responsible for pathogenesis and the establishment of successful infections by interfering with bacterial communication systems [1,7] This coupled with their extensive usage against infectious diseases both in traditional and modern medicines [3] makes them attractive in drug discovery. The quorum sensing (QS) inhibitory activity of K. africana fruit extracts was investigated using the Chromobacterium violaceum and Agrobacterium tumefaciens biosensor systems
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