Abstract
Biofilms facilitate the pathogenesis of life-threatening Pseudomonas aeruginosa infections by coating mucosal surfaces or invasive devices and offer protection from antimicrobial therapy and the host immune response, thus increasing mortality rates and financial burden. Herein, new hybrid N-acylcysteines (NAC) incorporating selected acyl groups from organic acids and their derivatives, which are capable of quenching pathogen quorum sensing (QS) systems, were designed and their antibiofilm activity and anti-QS were evaluated. N-acylcysteines (4a–h) were synthesized and characterized by 1H NMR and 13C NMR, and their purity was confirmed by elemental analyses. N-(4-Hydroxy-3,5-dimethoxybenzoyl)-l-cysteine (4d) and N-(4-methoxybenzoyl)-l-cysteine (4h) showed a higher antibiofilm activity against PAO1 biofilms than the rest of the targets and the standard NAC. They showed 83 and 82% inhibition of biofilms at 5 mM and eradicated mature biofilms at 20 mM concentrations (NAC biofilm inhibition = 66% at 10 mM and minimum biofilm eradication concentration = 40 mM). This was confirmed via visualizing adherent biofilm cells on catheter pieces using scanning electron microscopy. In the same vein, both 4d and 4h showed the highest docking score with the QS signal receptor protein LasR (−7.8), which was much higher than that of NAC (−5) but less than the score of the natural agonist N-(3-oxododecanoyl)-l-homoserine (OdDHL) (−8.5). Target 4h (5 mM) decreased the expression of quorum sensing encoding genes in P. aeruginosa PAO1 strain by 53% for pslA, 47% for lasI and lasR, and 29% for filC, lowered PAO1 pyocyanin production by 76.43%, completely blocked the proteolytic activity of PAO1, and did not affect PAO1 cell viability. Targets 4d and 4h may find applications for the prevention and treatment of biofilm-mediated P. aeruginosa local infections of the skin, eye, and wounds. N-(4-Methoxybenzoyl)-l-cysteine 4h is a promising dual-acting matrix disruptive and anti-QS antibiofilm agent for further investigation and optimization.