L-leucine shows promising antibiofilm potential against Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen capable of forming biofilms that significantly reduce the efficacy of conventional antibiotics. The present study aimed to evaluate the antibiofilm potential of L-leucine through a systematic screening of 20 naturally occurring L-amino acids. Among the tested compounds, L-leucine exhibited the highest activity, achieving 49.8 ± 2.1% biofilm inhibition at 30 µg/mL (n = 3, p < 0.001), as determined by crystal violet staining, extracellular polysaccharide quantification, and total protein analysis. Importantly, L-leucine at the tested concentrations (10-30 µg/mL) did not significantly affect bacterial growth ( p > 0.05), suggesting that the observed effect is independent of antimicrobial activity. Further analysis revealed that L-leucine reduced key factors associated with biofilm formation, including cell surface hydrophobicity, auto-aggregation, and motility, along with a measurable decrease in pyocyanin production. In addition, partial biofilm disruption (~39%) was observed within 4 h of treatment. Molecular docking suggested a weak interaction between L-leucine and the quorum sensing (QS) synthase LasI (binding affinity: -4.10 kcal/mol), which was supported by concentration-dependent downregulation of the QS-associated gene lasI . However, given the limited molecular evidence, these findings suggest a possible role in QS-associated modulation rather than definitive QS inhibition. Overall, the study demonstrates that L-leucine exhibits notable in vitro antibiofilm activity against P. aeruginosa under sub-inhibitory conditions. Further investigations, including multi-target QS analysis and in vivo validation, are required to establish its mechanistic role and potential applicability.