Essential Oil Compositions and Antimicrobial Activities of <i>Syzygium fluviatile</i> (Hemsl.) Merr. &amp; L.M.Perry: A Comparative Study on Collection Regions

Objective Essential oils extracted from Syzygium species are known for various pharmacological purposes. Syzygium fluviatile (Hemsl.) Merr. &amp; L.M.Perry is a flowering plant found in China and Vietnam. The current study aims to offer a comparison of chemical compositions in essential oils of S. fluviatile fruits and leaves, collected from five regions of Vietnam. The obtained oils were also taken into antimicrobial consideration, which was further aided by in silico approaches. Methods Phytochemical analysis of essential oils was carried out using GC-FID/MS (gas chromatography-flame ionization detection/mass spectrometry) analysis. An antimicrobial assay was performed using broth micro-dilution for in vitro screening. In silico considerations are mainly based on docking studies and toxicity assessments using the AutoDock Vina v1.2.3 program and the ProTox 3.0 web server, respectively. Results Hydro-distillation of S. fluviatile fresh fruits and leaves can lead to the production of yellow essential oil with yields of 0.21–0.32% v/w. In general, the obtained oils were dominated by monoterpene and sesquiterpene derivatives, as well as ( E)-caryophyllene (8.40-47.12%) being the principal compound. The oil samples showed strong antimicrobial activity against the Gram (+) bacteria Enterococcus faecalis ATCC51299, Staphylococcus aureus ATCC29213, and Bacillus cereus ATCC11778, and the yeast Candida albicans ATCC 60193 with the MIC and IC 50 values 16–64 µg/mL and 5.12–24.68 µg/mL. Docking results indicated that ( E)-caryophyllene exhibited binding affinities from −6.728 kcal/mol to −5.729 kcal/mol with important amino acid residues in the DNA gyrase, PBP3, and SAP2 targets. The toxicity profile of ( E)-caryophyllene is also discussed. Conclusion The isolation of ( E)-caryophyllene from Vietnamese Syzygium essential oils as a purified compound is necessary. In vivo antimicrobial studies and molecular mechanisms of action are needed.