Composition and Antibacterial Activity of the Essential Oils of Orthosiphon stamineus Benth and Ficus deltoidea Jack against Pathogenic Oral Bacteria

Abstract

In this study, the essential oils of <i>Orthosiphon stamineus</i> Benth and <i>Ficus deltoidea</i> Jack were evaluated for their antibacterial activity against invasive oral pathogens, namely <i>Enterococcus faecalis</i>, <i>Streptococcus mutans</i>, <i>Streptococcus mitis</i>, <i>Streptococcus salivarius</i>, <i>Aggregatibacter actinomycetemcomitans</i>, <i>Porphyromonas gingivalis</i> and <i>Fusobacterium nucleatum</i>. Chemical composition of the oils was analyzed using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The antibacterial activity of the oils and their major constituents were investigated using the broth microdilution method (minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC)). Susceptibility test, anti-adhesion, anti-biofilm, checkerboard and time-kill assays were also carried out. Physiological changes of the bacterial cells after exposure to the oils were observed under the field emission scanning electron microscope (FESEM). <i>O. stamineus</i> and <i>F. deltoidea</i> oils mainly consisted of sesquiterpenoids (44.6% and 60.9%, respectively), and β-caryophyllene was the most abundant compound in both oils (26.3% and 36.3%, respectively). Other compounds present in <i>O. stamineus</i> were α-humulene (5.1%) and eugenol (8.1%), while α-humulene (5.5%) and germacrene D (7.7%) were dominant in <i>F. deltoidea</i>. The oils of both plants showed moderate to strong inhibition against all tested bacteria with MIC and MBC values ranging 0.63-2.5 mg/mL. However, none showed any inhibition on monospecies biofilms. The time-kill assay showed that combination of both oils with amoxicillin at concentrations of 1× and 2× MIC values demonstrated additive antibacterial effect. The FESEM study showed that both oils produced significant alterations on the cells of Gram-negative bacteria as they became pleomorphic and lysed. In conclusion, the study indicated that the oils of <i>O. stamineus</i> and <i>F. deltoidea</i> possessed moderate to strong antibacterial properties against the seven strains pathogenic oral bacteria and may have caused disturbances of membrane structure or cell wall of the bacteria.