Arrest Bacterial Communication: Interfering with Quorum Sensing to Inhibit Biofilm Formation
Are you hesitant to enter the hospital emergency room, fearing that you may get infected with deadly bacteria? Well, this is something many of us are concerned about these days. The threat of multidrug-resistant bacteria, commonly referred to as ‘Superbugs’, is increasing day by day. A recent alarming case was reported in Nevada, USA, where a woman died due to an untreatable medical condition caused by a Klebsiella pneumoniae superbug.
This multidrug-resistant K. pneumoniae is a Gram-negative bacterium categorized as CRE: carbapenem-resistant Enterobacteriaceae. It often causes severe urinary tract infections (UTIs), which can progress into systemic bloodstream infections. What was alarming was the fact that this pathogen was resistant to 26 different antibiotics. Clinicians and scientists believe that antibiotic-resistant bacteria could cause up to 10 million deaths per year by 2050 if left unchecked. Thus, there is growing concern around the treatment and management of drug-resistant bacterial infections [1].
It is interesting to note that nearly all multidrug-resistant bacteria can form biofilms, which make them extremely difficult to eradicate. In bacterial biofilms, microbes live in cooperative communities embedded within a self-produced extracellular polymeric matrix. One key mechanism involved in this behavior is quorum sensing (QS): a phenomenon by which bacteria communicate and coordinate group behavior. Quorum sensing plays an essential role in biofilm formation and bacterial virulence.
QS regulates gene expression responsible for phenotypes that are crucial to pathogenicity and symbiosis through autoinducer signaling molecules. In Gram-negative bacteria, quorum sensing is mediated by N-acyl homoserine lactones (AHLs). QS controls the production of virulence factors such as exopolysaccharide synthesis, swarming motility, biofilm formation, and toxin and pigment production in many pathogenic organisms.
Because of the rapid emergence of antibiotic resistance and the central role of QS in bacterial pathogenesis, interfering with quorum sensing has emerged as a promising antivirulence strategy. Unlike conventional antibiotics, quorum sensing inhibitory (QSI) compounds do not kill bacteria or inhibit their growth directly. As a result, they are less likely to promote the development of resistance. Recent studies have identified several natural products, including plant extracts, that exhibit QS-modulating properties, thereby reducing bacterial virulence [2–4].
Different bacterial strains can be used to study quorum sensing, and one of the most commonly used model organisms is Chromobacterium violaceum (C. violaceum).
C. violaceum is a Gram-negative bacterium that produces a distinctive purple pigment called violacein in response to QS-regulated gene expression mediated by AHLs. It is a widely used and efficient model microorganism for quorum sensing studies. The wild-type C. violaceum strain constitutively expresses AHL and produces purple pigment on agar plates. In contrast, the biosensor strain C. violaceum CV026 (a mini-Tn5 mutant) lacks AHL synthase activity and only produces pigment when exogenous AHL is present.
Both strains are ideal for studying QS pathways and offer a convenient and visual approach for identifying quorum sensing inhibitors (QSIs) or antagonists.
At Emery Pharma, we offer quorum sensing inhibition (QSI) assays for identifying QSI activity in plant extracts and test articles using both wild-type and mutant strains of C. violaceum. When a plant extract or compound contains a QSI or antagonist, it interferes with violacein production, resulting in a zone of colorlessness around the plant material or disc on the agar — even though bacterial growth remains unaffected.
The image on the left is a representative result from a recent QSI screening study conducted at Emery Pharma. It shows clear zones of growth inhibition and zones of colorlessness, indicating suppression of QS-mediated pigment production by a plant-based test article. At sub-lethal concentrations, inhibition of violacein (without bacterial death) signifies quorum sensing inhibition.
Emery Pharma offers quorum sensing assays, QSI screening, and a range of microbiological testing services. Our team of Ph.D. and M.Sc. scientists not only performs these tests with scientific rigor but also provides expert guidance in designing your study, selecting the best mechanism of action, answering your technical questions, and delivering detailed scientific analysis of the results.
About the author:
Sridhar Arumugam holds a Ph.D. degree in Microbiology and he is the Director of Cell and Microbiology with Emery Pharma.
References
- Kostyanev, T., Bonten, M.J. and Goossens, H., 2017. Anti-infectives and the Lung: ERS Monograph 75, 75, p.289.
- McClean KH, Winson MK, Fish L, Taylor A, Chhabra SR, Camara M, Daykin M, Lamb JH, Swift S, Bycroft BW, Stewart GS. Quorum sensing and Chromobacterium violaceum: exploitation of violacein production and inhibition for the detection of N-acylhomoserine lactones. Microbiology. 1997 Dec 1;143(12):3703-11.
- Vasavi HS, Arun AB, Rekha PD. Inhibition of quorum sensing in Chromobacterium violaceum by Syzygium cumini L. and Pimenta dioica L. Asian Pacific journal of tropical biomedicine. 2013 Dec 31;3(12):954-9.
- McLean RJ, Pierson LS, Fuqua C. A simple screening protocol for the identification of quorum signal antagonists. Journal of Microbiological Methods. 2004 Sep 30;58(3):351-60.
