Modulation of quorum sensing-controlled virulence factors in Chromobacterium violaceum by selective amino acids.

Bacterial pathogenesis regulation requires N-acyl homoserine lactone (AHL)-based quorum sensing (QS). The main objective of this study was to assess the anti-QS and anti-biofilm potential of five different amino acids, namely serine, aspartic acid, lysine, leucine and tryptophan. The selected amino acids were assessed for their ability to inhibit QS activity via such mechanisms as exopolysaccharide (EPS) production, biofilm formation, pigment production in Chromobacterium violaceum and swarming motility. At 0.684 mM concentration, lysine inhibited the biofilm formation by 16% at 24 h, chitinolytic activity by 88.3% at 24 h and EPS production by 12.5% at 24 h. It also exhibited inhibition of swarming motility in C. violaceum. Confocal laser scanning microscopy revealed a decrease in the average thickness of the biofilms when treated with lysine. Modulation in the expression of cvi I and cvi A was observed when treated with all the amino acids, with the greatest reduction observed with lysine. Our results conclude that the amino acid lysine showed anti-QS and significant anti-biofilm activities; it could be further exploited as a main constituent in the synthesis of peptide/protein, and testing the same for treatment of bacterial infections, eventually reducing the utilization of conventional antibiotics.