Abstract
Many essential oils (EOs) regulate the quorum-sensing (QS) system of pathogens and inhibit the virulence expression. Interference with QS can potentially reduce bacterial multidrug resistance and aid the biological control of bacterial disease. In the present work, the antibacterial and anti-QS activities of Cinnamomum camphora leaf EO were investigated. A total of 23 chemical components with relative levels ≥0.11%, including a large number of terpene compounds, were identified in C. camphora leaf EO by gas chromatography–mass spectrometry (GC-MS). The principal component was linalool, followed by eucalyptol, with relative levels of 51.57% and 22.07%, respectively. The minimum inhibitory concentration (MIC) and antibacterial activity of C. camphora EO were examined, and P. aeruginosa and E. coli ATCC25922 showed the highest and lowest sensitivity to C. camphora EO, respectively. Tests of QS inhibitory activity revealed that C. camphora EO significantly decreased the production of violacein and biofilm biomass in C. violaceum, with the maximum inhibition rates of 63% and 77.64%, respectively, and inhibited the biofilm formation and swarming movement, independent of affecting the growth of C. violaceum. Addition of C. camphora EO also resulted in downregulation of the expression of the acyl-homoserine lactones (AHL) synthesis gene (cviI) and transcription regulator (cviR), and inhibited the expression of QS-regulated virulence genes, including vioA, vioB, vioC, vioD, vioE, lasA, lasB, pilE3, and hmsHNFR. Collectively, the prominent antibacterial activity and anti-QS activities clearly support that C. camphora EO acts as a potential antibacterial agent and QS inhibitor in the prevention of bacterial contamination.
Highlights
In recent years, antibiotics and antimicrobial agents have been widely used for the prevention and control of bacterial diseases
A total ion flow chromatogram of the C. camphora essential oils (EOs) analyzed by gas chromatography–mass spectrometry (GC-MS)
Our results showed that C. camphora EO inhibited stage of quorum sensing (QS)-regulated bacterial biofilm formation
Summary
Antibiotics and antimicrobial agents have been widely used for the prevention and control of bacterial diseases. Traditional antimicrobial agents inhibit and kill bacteria by interfering with their biochemical metabolism as well as by affecting their structure and functions [1]. Bacteria rapidly mutate under selective pressure, which results in rapid increases in drug-resistant bacteria and leads to many difficulties in the prevention and treatment of bacterial diseases. The discovery of different novel therapies to treat or decrease cases of bacterial infections is urgently required. Inhibition of quorum sensing (QS) may be a suitable solution.
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