Free tryptophan residues inhibit quorum sensing of Pseudomonas aeruginosa: a potential approach to inhibit the development of microbial biofilm.

Microbial biofilm reveals a cluster of microbial population aggregated on a surface. Pseudomonas aeruginosa, a strong biofilm forming organism, often causes several human diseases. Microorganism-based diseases become more difficult to manage when the causative organism develops biofilm during the course of disease progression as the organism attains alarming drug resistance in biofilm form. Agents inhibiting microbial biofilm formation could be considered as a potential tool to weaken the extent of microbial pathogenesis. Tryptophan has already been reported as a promising agent against the biofilm development by P. aeruginosa. In the current study, we had focused on the underlying mechanism of microbial biofilm inhibition of P. aeruginosa under the influence of tryptophan. The expression level of the mRNA of the genes (lasR, lasB and lasI) associated with quorum sensing was compared between tryptophan treated and untreated cells under similar conditions using real time polymerase chain reaction (RT-PCR). The results showed that the tested concentrations of tryptophan considerably reduced the expression of those genes (lasR, lasB and lasI) that are required during the occurrence of quorum sensing in P. aeruginosa. Molecular docking also revealed that tryptophan can interact with the proteins responsible for the occurrence of quorum sensing in P. aeruginosa. The cytotoxicity assay was carried out wherein we observed that the tested concentration of tryptophan did not show any considerable cytotoxicity against the RAW 264.7 macrophage cell line. From this study, it may be concluded that the tryptophan-mediated inhibition of biofilm formation is associated with interference of quorum sensing in P. aeruginosa. Hence, tryptophan could be used as a potential agent against the microbial biofilm mediated pathogenesis.