Antibiofilm and Microbiome-Modulatory Effects of Syzygium aromaticum Essential Oil in an In Vitro Dental Caries Polymicrobial Model

Abstract

Background: Dental caries is a microbiome-driven disease in which acidogenic taxa dominated by Streptococcus mutans displace commensal genera and form a glucan-rich biofilm matrix that demineralises enamel. Chlorhexidine (CHX) is the standard chemical adjunct but causes staining, dysgeusia and broad commensal suppression, motivating evaluation of botanical alternatives that may rebalance the oral ecosystem.

Objective: To determine the antibiofilm and microbiome-modulatory effects of standardised Indonesian Syzygium aromaticum L. (clove, Myrtaceae) bud essential oil (SAEO) on saliva-derived polymicrobial cariogenic biofilms in vitro.

Methods: SAEO was hydrodistilled, characterised by gas chromatography–mass spectrometry (GC-MS), and tested at SAEO 0.25%, 0.5% and 1.0% v/v against polymicrobial biofilms grown on hydroxyapatite discs from stimulated saliva of 60 caries-active adults; CHX 0.12% was the positive control (n = 6 per arm). Endpoints were biofilm biomass, colony-forming units (CFU) on selective media, extracellular polymeric substance (EPS), biofilm pH, lactate, 16S rRNA microbiome profiling and human gingival fibroblast (HGF-1) cytotoxicity.

Results: Eugenol (82.3%), β-caryophyllene (7.4%) and eugenyl acetate (4.8%) were the principal volatiles. SAEO 1.0% reduced biofilm biomass by 70.5% (95% CI 65.8–75.3; p < 0.001), S. mutans CFU by 3.22 log₁₀ and EPS by 67.9%, while raising Shannon diversity from 1.42 to 2.08 bits and restoring Neisseria and Corynebacterium relative abundance — a dysbiosis-reversal pattern absent under CHX. Cytotoxicity reached 17.6% at SAEO 1.0% versus 31.8% for CHX 0.12%.

Conclusion: Standardised SAEO is a credible complementary anticaries agent meriting clinical translation.