Anti-quorum sensing activity of selected cationic amino acids against Chromobacterium violaceum and Pseudomonas aeruginosa

Antibiotic-resistant strains and superbugs have emerged as a result of unrestricted use and overuse of antibiotics. N-Acyl homoserine lactones, also known as autoinducers, are unique type of signaling molecule and passively permeate to the cells of Gram-negative bacteria. Accumulation of signaling molecules in the environment regulates the bacterial population. The organisms Pseudomonas aeruginosa and Chromobacterium violaceum are Gram-negative bacteria when exposed to humans, cause fatal infections. The selected cationic amino acids histidine, arginine, and ornithine were assessed for their anti-quorum sensing activity against the P. aeruginosa and C. violaceum. The MIC and sub-MIC concentrations of the selected amino acids have been found by the broth dilution method. Both the cultures have been treated with MIC and sub-MIC levels and the virulence factors like rhamnolipid, protease, elastase, pyoverdine, pyocyanin for P. aeruginosa and violacein, chitinase for C. violaceum is quantified. The quantification of exo-polysaccharides and the biofilm as well as visualization by confocal laser scanning microscope have been done for both organisms. The movement of the cells was assessed by swarming and swimming motility in both organisms. The genes activated for all these virulence factors were quantified by RT-qPCR and expressed in fold change. From the results, it is evident that the histidine inhibited both the organisms at concentrations of MIC and sub-MIC more than the percentage of virulence factors production by arginine and ornithine. The selected cationic amino acids prove to be an effective compound in antimicrobial therapeutics in order to reduce opportunistic bacterial infections.

Automated summary

The study evaluated the anti-quorum sensing activity of selected cationic amino acids histidine, arginine, and ornithine against P. aeruginosa and C. violaceum. Results showed that histidine had a stronger inhibitory effect on both organisms at MIC and sub-MIC concentrations.