title: Isoprenyl caffeate, a major compound in manuka propolis, is a quorum-sensing inhibitor in Chromobacterium violaceum.
abstract: The emergence of antibiotic-resistant bacterial pathogens, especially Gram-negative bacteria, has driven investigations into suppressing bacterial virulence via quorum sensing (QS) inhibition strategies instead of bactericidal and bacteriostatic approaches. Here, we investigated several bee products for potential compound(s) that exhibit significant QS inhibitory (QSI) properties at the phenotypic and molecular levels in Chromobacterium violaceum ATCC 12472 as a model organism. Manuka propolis produced the strongest violacein inhibition on C. violaceum lawn agar, while bee pollen had no detectable QSI activity and honey had bactericidal activity. Fractionated manuka propolis (pooled fraction 5 or PF5) exhibited the largest violacein inhibition zone (24.5 ± 2.5 mm) at 1 mg dry weight per disc. In C. violaceum liquid cultures, at least 450 µg/ml of manuka propolis PF5 completely inhibited violacein production. Gene expression studies of the vioABCDE operon, involved in violacein biosynthesis, showed significant (≥two-fold) down-regulation of vioA, vioD and vioE in response to manuka propolis PF5. A potential QSI compound identified in manuka propolis PF5 is a hydroxycinnamic acid-derivative, isoprenyl caffeate, with a [M-H] of 247. Complete violacein inhibition in C. violaceum liquid cultures was achieved with at least 50 µg/ml of commercial isoprenyl caffeate. In silico docking experiments suggest that isoprenyl caffeate may act as an inhibitor of the violacein biosynthetic pathway by acting as a competitor for the FAD-binding pockets of VioD and VioA. Further studies on these compounds are warranted toward the development of anti-pathogenic drugs as adjuvants to conventional antibiotic treatments, especially in antibiotic-resistant bacterial infections.
authors.affiliation: Department of Biotechnology, Faculty of Applied Sciences, UCSI University, No 1, Jalan Menara Gading, UCSI Heights, 56000, Cheras, Kuala Lumpur, Malaysia.
authors.forename: Adrian Tandhyka
authors.initials: AT
authors.lastname: Gemiarto
authors.forename: Nathaniel Nyakaat
authors.initials: NN
authors.lastname: Ninyio
authors.forename: Siew Wei
authors.initials: SW
authors.lastname: Lee
authors.forename: Joko
authors.initials: J
authors.lastname: Logis
authors.forename: Ayesha
authors.initials: A
authors.lastname: Fatima
authors.forename: Eric Wei Chiang
authors.initials: EW
authors.lastname: Chan
authors.forename: Crystale Siew Ying
authors.initials: CS
authors.lastname: Lim
mesh_terms: D053898:Biosynthetic Pathways / Q000187:drug effects; D002109:Caffeic Acids / Q000378:metabolism*; D002861:Chromobacterium / Q000187:drug effects* / Q000502:physiology*; D020869:Gene Expression Profiling; D007211:Indoles / Q000037:antagonists & inhibitors*; D050296:Microbial Viability / Q000187:drug effects; D062105:Molecular Docking Simulation; D011429:Propolis / Q000737:chemistry*; D053038:Quorum Sensing / Q000187:drug effects*; D014774:Virulence / Q000187:drug effects
chemical_list: D002109:Caffeic Acids; D007211:Indoles; C054126:1,1-dimethylallyl caffeic acid ester; D011429:Propolis; C063155:violacein