Purpose: Zedoary turmeric oil (ZTO), the steam extract of Curcuma zedoaria Rosc was researched for its chemical composition, antibacterial activity, and mechanism for countering two major food-borne pathogenic species, Listeria monocytogenes and Staphylococcus aureus.
Methodology: Gas chromatography-mass spectrometry (GC-MS) was used to analyse and characterize the chemical composition of ZTO. Its MICs for the two bacterial species and growth curves were measured. Western blot and real-time reverse-transcription (RT)-PCR assays were utilized to elaborate the mechanism of the antibacterial effect of ZTO by examining the expression levels of virulence-related extracellular proteins. ELISA was used to explore the biological relevance.
Results: GC-MS revealed high contents of curzerene, eucalyptol, germacrone and (-)-g-elemene representing 28.45, 10.94, 10.77 and 10.54 %, respectively, of the whole components. The MICs of ZTO that combatted L. monocytogenes and S. aureus were similar (1-2 mg ml-1 ). After adding ZTO at increasing concentrations, there was an evident reduction in the transcription of hly, iap, hla, sea, seb and agrA in a dose-dependent manner. Furthermore, TNF-α accumulation in RAW264.7 cells stimulated by L. monocytogenes and S. aureus supernatants was restricted by a 1/4 MIC of ZTO.
Conclusion: Overall, L. monocytogenes and S. aureus were comparably susceptible to ZTO. These data demonstrated that ZTO's antimicrobial property was mediated by the repression of the production of virulence factors involved in L. monocytogenes and S. aureus pathogenesis, a finding that can potentially further progress in the development of new anti-virulence drugs.
Keywords: Listeria monocytogenes; Staphylococcus aureus; Zedoary turmeric oil; essential oil composition; virulence factors.