Abstract
Essential oils (EOs) or their components are widely used by inhalation or nebulization to fight mild respiratory bacterial infections. However, their interaction with antibiotics is poorly known. In this study we evaluated the effects of citral, the main component of lemongrass oil, on in vitro susceptibility of Pseudomonas aeruginosa to antibiotics. Exposure of strain PA14 to subinhibitory concentrations of citral increased expression of operons encoding the multidrug efflux systems MexEF-OprN and MexXY/OprM, and bacterial resistance to anti-pseudomonal antibiotics including imipenem (twofold), gentamicin (eightfold), tobramycin (eightfold), ciprofloxacin (twofold), and colistin (≥128-fold). Use of pump deletion mutants showed that in addition to efflux other mechanisms were involved in this citral-induced phenotype. Determination of Zeta potential suggested that citral impairs the cell surface binding of aminoglycosides and colistin used at low concentrations (≤10 μg/mL). Moreover, experiments based on Raman spectroscopy and high-resolution mass spectrometry demonstrated formation of a Schiff base between the aldehyde group of citral and amino-groups of tobramycin and colistin. Chemical synthesis of tobracitryl, the imine compound resulting from condensation of citral and tobramycin, confirmed the loss of antibiotic activity due to adduct formation. Altogether these data point to the potential risk concern of self-medication with EOs containing citral in patients suffering from P. aeruginosa chronic lung infections and being treated with aerosols of aminoglycoside or colistin.
Highlights
Essential oils (EOs) are complex mixtures of volatile compounds, produced by plants
We studied the impact of the acyclic aldehyde citral on the susceptibility of P. aeruginosa to several antibiotics commonly prescribed to treat cystic fibrosis (CF) lung infections
As no inhibition zone appeared around disks loaded with 5 μL (4.44 mg) citral, we monitored the growth of PA14 exposed to increasing concentrations of the compound
Summary
Essential oils (EOs) are complex mixtures of volatile compounds, produced by plants. Some possess antimicrobial activities, and are commonly used as self-medication to treat mild respiratory infections (Inouye et al, 2001). In the foodborne pathogen Cronobacter sakasakii, this aldehyde triggers pleiotropic effects including a shift in ATP concentration, acidification of the cytosol, cell membrane hyperpolarization, and damages to the cell wall, that would result in or contribute to cell death (Shi et al, 2016). Beside these alterations, citral is able to lower the production of virulence factors in Vibrio parahaemolyticus (Sun et al, 2019) and C. sakazakii (Shi et al, 2017), as well as to prevent the synthesis of quorum sensing auto-inducer N-dodecanoyl-L-homoserine lactone in Pseudomonas putida (Jaramillo-Colorado et al, 2012). Because of these different properties, citral might have potential applications in the treatment of some bacterial infections (Shah et al, 2011)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
