Chemical Composition and Disruption of Quorum Sensing Signaling in Geographically Diverse United States Propolis

Figure 1

Inhibition of AHL-dependent violacein synthesis in C. violaceum strain CV026 in the presence of United States propolis. (a) Inhibition of AHL-regulated violacein synthesis in CV026 by the selected propolis in the disc diffusion assay. Abbreviations include the following: 3OC12, positive control disc impregnated with long-chain 3-oxo-C12-HSL AHL signal. Others include the following: Hg, an internal standard, the Hungarian raw propolis to visualize violacein synthesis inhibition as a translucent zone adjacent to the disc and as previously reported by our laboratory [25]; EtOH, pure solvent of 70% ethyl alcohol (control); and Gm, antibiotic gentamycin to visualize biosensor death as a transparent zone adjacent to the disc. All experiments were performed in triplicate and (a) are a representative result of one replication. (b) Quorum sensing inhibition (QSI) by propolis samples in millimeters indicated by a translucent zone of violacein synthesis across the cellulose disc. Data presented is mean ± standard deviation. Data is also presented as percent of the Hungarian raw propolis (internal standard) (Hg). (c) Quantification of violacein pigment synthesis inhibition in CV026 after treatment with propolis. This data is presented as percent of violacein present in the soft agar plate background (positive control, full induction of violacein synthesis). Using the propolis samples, no CV026 biosensor growth inhibition (only observed in the antibiotic gentimycin containing disc) was observed as identified by transparent zone around the cellulose disc. All experiments were repeated at least three times with representative data of one experiment shown.

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