Essential Oils of Five Syzygium Species Growing Wild in Vietnam: Chemical Compositions and Antimicrobial and Mosquito Larvicidal Potentials.

The essential oils of five Vietnamese Syzygium species ( Syzygium levinei , S. acuminatissimum , S. vestitum , S. cumini , and S. buxifolium ) were first hydro-distilled and analyzed using GC-FID/MS (gas chromatography-flame ionization detection/mass spectrometry). Monoterpene hydrocarbons, sesquiterpene hydrocarbons, and oxygenated sesquiterpenoids were the main chemical classes in these oils. All these essential oils showed good-excellent antimicrobial activities against Gram-positive bacteria Enterococcus faecalis , Staphylococcus aureus , and Bacillus cereus , and the yeast Candida albicans. S. levinei leaf essential oil, rich in bicyclogermacrene (25.3%), ( E )- β -elemene (12.2%), ( E )-caryophyllene (8.2%), and β -selinene (7.4%), as well as S. acuminatissimum fruit essential oil containing ( E )-caryophyllene (14.2%), α -pinene (12.1%), caryophyllene oxide (10.9%), β -selinene (10.8%), α -selinene (8.0%), and α -humulene (5.7%), established the same MIC value of 8 µg/mL against E. faecalis and B. cereus , which were much better than the positive control streptomycin (MIC 128-256 µg/mL). The studied essential oils showed the potential to defend against mosquitoes since they caused the 24 and 48 h LC 50 values of less than 50 µg/mL against the growth of Culex quinquefasciatus and Aedes aegypti larvae. Especially, S. buxifolium leaf essential oil strongly inhibited Ae. aegypti larvae with 24 and 48 h LC 50 values of 6.73 and 6.73 µg/mL, respectively, and 24 and 48 h LC 90 values of 13.37 and 10.83 µg/mL, respectively. These findings imply that Vietnamese Syzygium essential oils might have potential for use as supplemental antibacterial agents or as "green" alternatives for the control of mosquitoes.