Synergistic Quorum quenching activity of Cinnamaldehyde against biofilm forming Pseudomonas aeruginosa

Quorum sensing is an essential mechanism for the pathogenesis of Pseudomonas aeruginosa, which causes opportunistic infections in humans. Quorum sensing inhibition has been considered a unique strategy to treat opportunistic infections and prevent an early event of infection without killing bacterial cells. The present study has demonstrated that cinnamaldehyde is able to inhibit biofilm formation by interfering with the quorum sensing activity of P. aeruginosa and is also able to disperse biofilms if they have already formed. It was also proven that synergistic action between 2.5 μM of cinnamaldehyde and 1 μM of cephalexin was effective in controlling biofilm formation. Cephalexin combined with cinnamaldehyde repressed the virulence factors associated with biofilms in Pseudomonas aeruginosa, such as Quorum sensing mediated motility, rhamnolipid, pyocyanin, elastase and rhamnolipid activities. A combination of cinnamaldehyde and cephalexin showed better biofilm inhibition (52.80%) than individual treatments and there was a reduction in the biofilm thickness and surface coverage among P. aeruginosa strains treated with cinnamaldehyde plus cephalexin. Further, it was also reported that the N-Hexanoylhomoserine lactone concentration was lower in P. aeruginosa strains treated with cinnamaldehyde plus cephalexin, while the control set-up showed a high amount of N-Hexanoylhomoserine lactone concentration. However, cinnamaldehyde with amoxycillin, oxacillin, or streptomycin showed a comparatively weaker quorum quenching effect when tested using checkerboard assays. Combination of CAD with CEPH can be a better alternative to treat P. aeruginosa infection.