Sub-MICs of Mentha piperita essential oil and menthol inhibits AHL mediated quorum sensing and biofilm of Gram-negative bacteria.

Fohad M Husain,Iqbal Ahmad,Ejaz Ahmad,Nasser A Alshabib,Mohd Shahnawaz Khan,Qudisa Tahseen,Mohammad S Khan

doi:10.3389/fmicb.2015.00420

Abstract

Bacterial quorum sensing (QS) is a density dependent communication system that regulates the expression of certain genes including production of virulence factors in many pathogens. Bioactive plant extract/compounds inhibiting QS regulated gene expression may be a potential candidate as antipathogenic drug. In this study anti-QS activity of peppermint (Mentha piperita) oil was first tested using the Chromobacterium violaceum CVO26 biosensor. Further, the findings of the present investigation revealed that peppermint oil (PMO) at sub-Minimum Inhibitory Concentrations (sub-MICs) strongly interfered with acyl homoserine lactone (AHL) regulated virulence factors and biofilm formation in Pseudomonas aeruginosa and Aeromonas hydrophila. The result of molecular docking analysis attributed the QS inhibitory activity exhibited by PMO to menthol. Assessment of ability of menthol to interfere with QS systems of various Gram-negative pathogens comprising diverse AHL molecules revealed that it reduced the AHL dependent production of violacein, virulence factors, and biofilm formation indicating broad-spectrum anti-QS activity. Using two Escherichia coli biosensors, MG4/pKDT17 and pEAL08-2, we also confirmed that menthol inhibited both the las and pqs QS systems. Further, findings of the in vivo studies with menthol on nematode model Caenorhabditis elegans showed significantly enhanced survival of the nematode. Our data identified menthol as a novel broad spectrum QS inhibitor.

Highlights

Emergence and spread of antibiotic resistance among pathogenic bacteria represents a major obstacle in treatment of infectious diseases
Effect of Peppermint Oil on Violacein Production Anti-quorum sensing (QS) property of M. piperita oil was firstly assessed for pigment inhibition in CVO26
Viable plate count performed on MHA plates at 24 h incubation showed no significant difference in the number of colony-forming units (CFUs) between untreated C. violaceum CVO26 and C. violaceum CVO26 treated with sub-Minimum Inhibitory Concentration (sub-MIC) of the oil (Figure 1)

Summary

Introduction

Emergence and spread of antibiotic resistance among pathogenic bacteria represents a major obstacle in treatment of infectious diseases. Bacterial quorum sensing (QS) has been identified as a promising anti-infective drug target (Hentzer et al, 2002). It would be possible to repress the expression of QS regulated phenotypes through which the development of biofilm and virulence are being accomplished in many Gram-negative bacterial pathogens; such interference is expected to be useful in the treatment of bacterial infections (Hentzer and Givskov, 2003; March and Bentley, 2004). The QS mechanism enables bacteria to detect their population density through the production, release, and perception of small diffusible molecules called autoinducers and to coordinate gene expression (Williams et al, 2007; Rumbaugh et al, 2012).A wide array of functions in bacteria ranging from bacterial cell motility to complex behaviors such as biofilm formation and production of virulence factors are regulated by QS in pathogenic bacteria (Atkinson et al, 2006; Rumbaugh and Armstrong, 2014). Several Gram-negative pathogens employ N-acyl homoserine lactones (AHLs)-mediated QS systems to coordinate and synchronize specific gene expression of particular phenotypic features between the individual cells (Fuqua et al, 1994)

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Conclusion