Assessment of shikonin and acetyl-shikonin for mitigating quorum sensing potential of C. violaceum

Shikonins (SK) and acetyl-shikonins (acetyl-SK) are known to possess great pharmaceutical potentials however, their ability to disrupt infectious bacterial communication system viz. quorum sensing (QS) remains unexplored. Therefore, the rationale behind this research was to investigate the QS-quenching potential of SK and acetyl-SK against C. violaceum through biofilm formation and violacein production assays. The quantitative evaluation was followed by the investigation of transcript abundance of violacein-regulating genes using RT-qPCR. Quantitative analysis indicated marked inhibition of QS-related traits with more obvious inhibition (87.5% biofilm, and 58% violacein inhibition) with 0.4 mM SK-treatment. Our RT-qPCR results displayed a substantially significant decrease in the expression level of CviR in SK-treated cells. Furthermore, SK treatment resulted in reduced transcript abundance of violacein biosynthetic genes such as vioB, vioC , and vioD . It was found that SK-induced QS inhibition in C. violaceum occurred through CviR down-regulation, which might further potentially disrupt the AHL-CviR receptor interaction. Both SK and acetyl-SK treatments were found to be ineffective against pre-mature biofilms, implying that SK-mediated biofilm attenuation is caused by interference with the expression of genes involved in biofilm attachment. In our study, SK strongly interfered with AHL-regulated physiological attributes while acetyl-SK was effective in inhibiting biofilm formation only. Collectively we found SK as anti-QS agents that mediate C. violaceum QS inhibition and bring new hope in combating C. violaceum infections. In addition, our findings can help prevent drug resistance in microbial pathogens in the future. Graphic abstract