Hordenine: A Novel Quorum Sensing Inhibitor and Antibiofilm Agent against Pseudomonas aeruginosa

The quorum sensing (QS) inhibitory activity of hordenine from sprouting barley against foodborne pathogen Pseudomonas aeruginosa was evaluated for the first time here. At concentrations ranging from 0.5 to 1.0 mg mL-1, hordenine inhibited the levels of acyl-homoserine lactones. The enhanced susceptibility of hordenine with netilmicin on P. aeruginosa PAO1 biofilm formation as well as their efficiency in disrupting preformed biofilms was also evaluated using scanning electron microscopy and confocal laser scanning microscopy (CLSM). Hordenine treatment inhibited the production of QS-related extracellular virulence factors of P. aeruginosa PAO1. Additionally, quantitative real-time polymerase chain reaction analysis demonstrated that the expressions of QS-related genes, lasI, lasR, rhlI, and rhlR, were significantly suppressed. Our results indicated that hordenine can serve as a competitive inhibitor for signaling molecules and act as a novel QS-based agent to defend against foodborne pathogens.