Quorum quenching activity of pentacyclic triterpenoids leads to inhibition of biofilm formation by Acinetobacter baumannii

Abstract

The quorum quenching (QQ) potential of three pentacyclic triterpenoids, glycyrrhetinic acid (GRA), ursolic acid (UA) and betulinic acid (BA), representing distinct groups of compounds, was evaluated. Violacein production by Chromobacterium violaceum and pyocyanin production by Pseudomonas aeruginosa were severely affected by GRA, UA and BA, suggesting a perturbation of N-acyl homoserine lactone (ASL) based signaling. Molecular docking analysis revealed a possible interaction between ASL-synthase and ASL-dependent transcriptional activator homologs from P. aeruginosa and Acinetobacter baumannii with common binding pockets for GRA, UA and BA. The triterpenoids inhibited biofilm formation by A. baumannii and affected the overall structure of biofilms. When administered in combination, two of the three molecules fostered antibiotic action against A. baumannii biofilms, widening the scope for developing novel combinations against the pathogen.

Keywords:

• Pentacyclic triterpenoids
• Acinetobacter baumannii
• biofilm
• quorum sensing

Acknowledgements

The authors acknowledge Prof. Sanjay Ghosh, Department of Biochemistry, University of Calcutta for his guidance and providing laboratory facilities when needed. The authors are also grateful to Prof. Tapas Sengupta and the Scanning Electron Microscopy division of IISER-Kolkata for their support. The authors would especially like to mention the FTIR facility of IACS, Kolkata for their constant support.

Disclosure statement

The authors declare no conflict of interest. None of the authors were paid from the funding for the project.

Author contributions

AS, SPB and AB designed the experiments. SPB and AM performed the experiment. AS, SPB, AM and AB analyzed the data and prepared the manuscript. All authorized and approved the final draft.

Additional information

Funding

This work was supported by Minor Research Grants for SP and AS from University Grants Commission (UGC), India (reference no. PSW-052/14-15 dated 06.09.2016).