Abstract
In this study, the essential oils of Orthosiphon stamineus Benth and Ficus deltoidea Jack were evaluated for their antibacterial activity against invasive oral pathogens, namely Enterococcus faecalis, Streptococcus mutans, Streptococcus mitis, Streptococcus salivarius, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis and Fusobacterium nucleatum. 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). O. stamineus and F. deltoidea 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 O. stamineus were α-humulene (5.1%) and eugenol (8.1%), while α-humulene (5.5%) and germacrene D (7.7%) were dominant in F. deltoidea. 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 O. stamineus and F. deltoidea 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.
Highlights
Oral health problems, periodontal diseases, dental caries and endodontic infections, are the most significant destructive processes in the oral cavity and are a costly burden to the public globally
This study focused on assessing the antibacterial properties as well as profiling the bioactive compounds of O. stamineus and F. deltoidea essential oils, with a high expectation to create and develop a highly effective intervention against invasive oral infections caused by different types of oral pathogens
The gas chromatography (GC) analysis of the oils resulted in identification of 30 and 40 compounds for O. stamineus and F. deltoidea, respectively
Summary
Periodontal diseases, dental caries and endodontic infections, are the most significant destructive processes in the oral cavity and are a costly burden to the public globally. Molecules 2017, 22, 2135; doi:10.3390/molecules22122135 www.mdpi.com/journal/molecules (tooth decay or cavities) are the most common and widespread chronic oral diseases that affect children and adults. They are irreversible infectious diseases of the teeth leading to cavities in the teeth structure, compromising the structure and function of the teeth [1,2]. Oral diseases are initiated by bacterial infection in the oral cavity and trigger inflammatory responses that will continue until the source of infection is removed through dental treatment of choice [3,4]. The combined ill effects of these major oral diseases weaken bodily defense and may serve as portal of entry to other more chronic and opportunistic infections
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