Manuka honey reduces the motility of Pseudomonas aeruginosa by suppression of flagella-associated genes

Objectives: Manuka honey is a broad-spectrum antimicrobial agent that seems to affect different bacteria in many different ways. It has been shown to be bactericidal against Pseudomonas aeruginosa by destabilizing the cell wall, but we aimed to investigate whether there were further intracellular target sites. Methods: In this study inhibitory effects of manuka honey on P. aeruginosa were investigated using hydrophobicity assays, two-dimensional electrophoresis, quantitative RT-PCR, transmission electron microscopy and motility assays. Results: Exposure of P. aeruginosa to manuka honey reduced both swarming and swimming motility. Moreover, this was a consequence of de-flagellation of the bacterial cell, whichwas correlated with decreased expression of the major structural flagellin protein, FliC, and concurrent suppression of flagellin-associated genes, including fliA, fliC, flhF, fleN, fleQ and fleR. The differential expression of the flagellar regulon in the presence of manuka honey was mapped schematically. Flagella are integral to bacterial adhesion, the initiation of infection and biofilm formation, and swarming has been associated with increased virulence. Conclusions: By limiting motility in vitro, we infer that manuka honey impacts on the virulence of P. aeruginosa. This deduction must now be tested in vivo.