Antibacterial Property of Synsepalum dulcificum Leaves Aqueous Extract against Oral Pathogens and its Chemical Compounds

@#Synsepalum dulcificum (S. dulcificum) commonly known as “miracle fruit” because its berries have the capability to modify sour taste to the sweet taste when eaten. Beside the berries, S. dulcificum leaves were also known to possess biological properties such as antioxidant, antimutagenic and antidiabetic activities. However, the study of its antimicrobial activity against oral pathogen is still lacking. Thus, this study aimed to evaluate the antibacterial activity of its leaves against cariogenic bacteria and to analyse its phytochemical compounds. The samples of S. dulcificum leaves were collected in Kelantan, the east coast region of Peninsular Malaysia and extracted with distilled water using a Soxhlet technique. The antibacterial activity of the S. dulcificum leaves aqueous extract against Streptococcus mutans (S. mutans), Streptococcus sobrinus (S. sobrinus) and Lactobacillus salivarius (L. salivarius) was evaluated using the broth microdilution assay. The identification of the phytochemical compounds was performed using gas chromatography-mass spectrometry (GC-MS). The antibacterial study showed the minimum inhibitory concentration of S. dulcificum leaves aqueous extract against S. mutans and S. sobrinus were 16 mg/mL and 8 mg/mL, respectively. Interestingly, there was no inhibitory effect of S. dulcificum leaves aqueous extract against L. salivarius. A total of 42 chemical compounds were identified and major identified bioactive compounds groups were heterocyclic and phenolic compounds. Our results suggested S. dulcificum leaves aqueous extract has antimicrobial properties against S. mutans and S. sobrinus, but no inhibitory activity against oral normal flora, with the presence of bioactive compounds has potential in oral care products application.

Antifungal activity and mechanism of action of monoterpenes against dermatophytes and yeasts

Dermatomycosis causes highly frequent dermal lesions, and volatile oils have been proven to be promising as antifungal agents. The antifungal activity of geraniol, nerol, citral, neral and geranial (monoterpenes), and terbinafine and anidulafungin (control drugs) against seven opportunistic pathogenic yeasts and four dermatophyte species was evaluated by the Clinical and Laboratory Standards Institute microdilution tests. Monoterpenes were more active against dermatophytes than yeasts (geometric mean of minimal inhibitory concentration (GMIC) of 34.5 and 100.4 µg.ml-1, respectively). Trichophyton rubrum was the fungal species most sensitive to monoterpenes (GMIC of 22.9 µg.ml-1). The trans isomers showed higher antifungal activity than the cis. The mechanism of action was investigated evaluating damage in the fungal cell wall (Sorbitol Protection Assay) and in the cell membrane (Ergosterol Affinity Assay). No changes were observed in the MIC of monoterpenes in the sorbitol protection assay.The MIC of citral and geraniol was increased from 32 to 160 µg.ml-1 when the exogenous ergosterol concentrations was zero and 250 µg.ml-1, respectively. The monoterpenes showed an affinity for ergosterol relating their mechanism of action to cell membrane destabilization.