The β-lactamase Inhibitor Boronic Acid SM23 Inhibits Pseudomonas aeruginosa Biofilm Formation and Virulence Factor Production

Introduction: Pseudomonas aeruginosa is a Gram-negative nosocomial pathogen, often responsible of severe device-related infections, given its great ability to produce biofilm. P. aeruginosa finely regulates the expression of different virulence factors, including biofilm production, by Quorum Sensing (QS), an intercellular communication mechanism used by many bacteria. Biofilm formation enhances bacterial resistance to antimicrobial agents due to a decreased penetration of antibiotics and a reduced rate of growth of embedded bacteria. Thus, novel agents capable of selective inhibiting biofilm formation may represent a promising strategy to overcome the well-known and widespread drug-resistance of P. aeruginosa. Material and Methods: by using the bioluminescent P. aeruginosa strain P1242, we investigated the effects of SM23, a boronic acid derivative specifically designed as beta-lactamase inhibitor, on biofilm formation and virulence factor production by P. aeruginosa. Results: we found that SM23: a) inhibited both biofilm formation and production of the virulence factors, pyoverdine, elastase and pyocyanin, without affecting bacterial growth; b) decreased the levels of QS-related autoinducers molecules, namely 3-oxo-C12-HSL and C4-HSL, by reducing lasR/lasI system gene expression in the biofilm; c) failed to bind to bacterial cells that had been preincubated with P. aeruginosa-conditioned medium; d) reduced significantly P. aeruginosa biofilm and pyoverdine production on endotracheal tubes, an in vitro condition closely mimicking clinical settings. Discussion and Conclusions: taken together, our results indicate that, besides inhibiting beta-lactamase, the boronic acid SM23, can also act as potent inhibitor of P. aeruginosa virulence, by profoundly affecting biofilm and QS-related signals. These findings highlight potential application of this compound in the prevention and treatment of biofilm-associated P. aeruginosa infections.