Abstract:
BACKGROUND : Curative plants have reportedly been used to make
chewing sticks/toothbrushes intended for the treatment of oral
diseases. OBJECTIVE : The in vitro antibacterial activities of Azadirachta
indica, Pongamia pinnata, Psidium guajava, and Mangifera indica were
evaluated against Streptococcus mutans, along with the cytotoxicity
and antioxidant and synergistic potentials. The effect of M. indica on the
expression of crucial virulence genes spaP and gtfB of S. mutans was
determined. MATERIALS AND METHODS : The antibacterial activity was
determined using a modified microdilution method. The antioxidant
potential was evaluated using diphenyl picrylhydrazyl (DPPH), Griess
reagent, and nitroblue tetrazolium calorimetric assays. The synergistic
activity was investigated using a modified checkerboard method,
while the cytotoxicity was determined according to a cell proliferation
2,3‑Bis‑(2‑methoxy‑4‑nitro‑5‑sulfophenyl)‑2H‑tetrazolium‑5‑carboxanilide
salt assay. Reverse transcription was the chosen method for determining the
difference in expression of the spaP and gtfB genes after treatment with the
plant sample. RESULTS : M. indica and A. indica had the highest antibacterial
activity at concentrations of 0.3 mg/ml and 6.25 mg/ml, respectively. A. indica
had the best free radical scavenging of DPPH, exhibiting 50% inhibition
at 28.72 μg/ml; while M. indica showed better superoxide scavenging
potential than the positive control quercetin. Both M. indica and A. indica had
adequate activity against the nitric oxide‑free radical (12.87 and 18.89 μg/ml,
respectively). M. indica selectively reduced the expression of the gtfB gene,
indicating a mechanism involving Glucotranferases, specifically targeting
bacterial attachment. Conclusion: The overall good antibacterial activity
of M. indica correlated with the general good antioxidant capacity, while
showing a potentially unique mechanism of bacterial inhibition, targeting
virulence gene expression.
