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Background <p><i>Enterococcus faecalis</i> is a major cause of persistent endodontic infections due to its strong biofilm-forming ability and resistance to conventional disinfectants. Cinnamon (<i>Cinnamomum zeylanicum</i>) essential oil (EO) has been recognized for its antimicrobial properties; however, its poor solubility and stability limit its clinical application. This study evaluated the antibacterial efficacy of cinnamon EO and its nanoemulsion (EM) against multidrug-resistant <i>E. faecalis</i> and its biofilm-associated gene expression.</p> Methods <p>Cinnamon EO was extracted via Soxhlet and emulsified using combined low- and high-energy methods. The physicochemical properties were characterized by GC–MS, FTIR, dynamic light scattering, and zeta potential. Antimicrobial activity was assessed by agar well diffusion, MIC/MBC determination, growth curve analysis, and crystal violet biofilm assay. Gene expression changes (<i>fsrB</i>,<i> luxS</i>,<i> ebpR</i>,<i> ace</i>,<i> esp</i>,<i> epaA</i>, and <i>bopD</i>) were quantified by RT-qPCR.</p> Results <p>GC–MS identified trans-cinnamaldehyde (70.5%) as the main component of the essential oil. EM showed a mean droplet size of 231.4&#xa0;nm and a zeta potential of − 39.2 mV, indicating high stability. EM had MIC/MBC of 0.049% (v/v) relative to the 20% stock solution, and significantly reduced bacterial growth and biofilm biomass. RT-qPCR showed significant downregulation of quorum-sensing genes (<i>fsrB</i>,<i> luxS</i>), adhesion genes (<i>ebpR</i>,<i> ace</i>), and other biofilm-related genes (<i>esp</i>,<i> epaA</i>,<i> bopD</i>) after EM treatment.</p> Conclusion <p>Cinnamon EO nanoemulsion demonstrated better antibiofilm activity than native EO, likely due to improved solubility, stability, and bioavailability of trans-cinnamaldehyde. Its capacity to inhibit growth, disrupt quorum-sensing, and reduce adhesion-related gene expression supports its potential as a natural adjunct for treating biofilm-related endodontic infections.</p>

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Enhanced antibiofilm and gene-suppressive effects of cinnamon nanoemulsion against multidrug-resistant Enterococcus faecalis

  • 期刊论文

  • 发表日期：

    2026年2月24日

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  • Pourya Gholizadeh,
  • Reyhaneh Rahimzadeh,
  • Behnam Mohammadi-Ghalehbin,
  • Mohesn Arzanlou,
  • Narges Soozangar,
  • Hadi Feizi

摘要

Background

Enterococcus faecalis is a major cause of persistent endodontic infections due to its strong biofilm-forming ability and resistance to conventional disinfectants. Cinnamon (Cinnamomum zeylanicum) essential oil (EO) has been recognized for its antimicrobial properties; however, its poor solubility and stability limit its clinical application. This study evaluated the antibacterial efficacy of cinnamon EO and its nanoemulsion (EM) against multidrug-resistant E. faecalis and its biofilm-associated gene expression.

Methods

Cinnamon EO was extracted via Soxhlet and emulsified using combined low- and high-energy methods. The physicochemical properties were characterized by GC–MS, FTIR, dynamic light scattering, and zeta potential. Antimicrobial activity was assessed by agar well diffusion, MIC/MBC determination, growth curve analysis, and crystal violet biofilm assay. Gene expression changes (fsrB, luxS, ebpR, ace, esp, epaA, and bopD) were quantified by RT-qPCR.

Results

GC–MS identified trans-cinnamaldehyde (70.5%) as the main component of the essential oil. EM showed a mean droplet size of 231.4 nm and a zeta potential of − 39.2 mV, indicating high stability. EM had MIC/MBC of 0.049% (v/v) relative to the 20% stock solution, and significantly reduced bacterial growth and biofilm biomass. RT-qPCR showed significant downregulation of quorum-sensing genes (fsrB, luxS), adhesion genes (ebpR, ace), and other biofilm-related genes (esp, epaA, bopD) after EM treatment.

Conclusion

Cinnamon EO nanoemulsion demonstrated better antibiofilm activity than native EO, likely due to improved solubility, stability, and bioavailability of trans-cinnamaldehyde. Its capacity to inhibit growth, disrupt quorum-sensing, and reduce adhesion-related gene expression supports its potential as a natural adjunct for treating biofilm-related endodontic infections.