Chitosan encapsulation modulates the effect of trans-cinnamaldehyde on AHL-regulated quorum sensing activity

Quorum sensing (QS) is a chemical communication process involved in the regulation of cooperative and communal activities in bacteria such as virulence production, bioluminescence and biofilm formation. Hence, the inhibition of QS processes has been examined as a promising alternative to deal with bacterial pathogens using antibiotic-free-based therapies. Trans-cinnamaldehyde (CA) is an intensively studied compound that proved to inhibit QS activity by decreasing the DNA-binding ability of LuxR while inhibiting acylhomoserine lactone production. In this work, chitosan based nanocapsules laden with a high concentration of CA were applied to a transformed E. coli Top 10 strain fluorescence-based reporter. Colloidal stability was assessed in M9 medium. The encapsulation efficiency of hydrophobic compound CA (20 mM; >37%) was greater than hydrophilic compounds vanillin (20 mM; ∼20%) and caffeine (20 mM; ∼10%). Biosensor assay shows us that CA-laden nanocapsules exhibit higher QS inhibition activity than free CA and CA-laden nanoemulsions. This result indicated that nanocapsules can interact with E. coli via electrostatic interaction, while thus effectively deliver CA to the bacteria. We reasoned that electrostatic adsorption of the chitosan-coated nanocapsules to the bacterial cell envelope, is the mechanism that underpins the observed enhancement of the QS inhibition activity.