DECIPHERING STREPTOCOCCUS MUTANS FROM DENTAL CARIES: INTEGRATED EVALUATION OF PLANT-DERIVED COMPOUNDS, ESSENTIAL OILS AND BISMUTH OXIDE NANOPARTICLE AS ANTIVIRULENCE AGENTS

Srutilaya Harikrishnan, Krithika Sundaramoorthy, Dr. Mahalakshmi Krishnan, Dr. Sasikala Shanmugam*

ABSTRACT

Dental caries is a chronic biofilm-mediated oral disease in which Streptococcus mutans play a major role in disease
progression through acid production and biofilm formation. Increasing antimicrobial resistance and the limitations
of conventional antimicrobial agents have encouraged the exploration of plant-derived therapeutics and
nanotechnology-based alternatives for oral healthcare applications. Methods: Streptococcus mutans was isolated
from pediatric dental caries samples and evaluated for biofilm formation, antimicrobial susceptibility, and
sensitivity toward selected medicinal plant extracts, essential oils, and phyto-fabricated bismuth oxide
nanoparticles using standard microbiological methods, agar well diffusion, and MIC assays. Nanoparticles were
characterized using UV–Visible spectroscopy, FTIR, and DLS analysis. Results: Among 60 dental caries samples,
42 (70%) were positive for S. mutans, of which 76.1% were biofilm producers. Antimicrobial susceptibility testing
revealed higher resistance to methicillin (47.9%), ciprofloxacin (41.9%), gentamycin (32.6%), and penicillin
(32.4%), while clindamycin showed the highest sensitivity (86.86%). Antibacterial activity was evaluated at
concentrations of 100–400 μg/μL. Among the plant extracts, Piper betle (24.50 ± 2.64 mm) and Nigella sativa
(24.25 ± 1.70 mm) showed the highest inhibition zones. Clove oil demonstrated the highest antibacterial activity
among essential oils (25.75 ± 1.50 mm). Among the nanoparticles, aqueous-mediated Piper betle nanoparticles
exhibited the highest activity (24.50 ± 1.29 mm). UV–Visible spectroscopy showed absorption peaks at 220–240
nm, while FTIR and DLS confirmed nanoparticle stabilization and nanoscale distribution. Conclusion: Essential
oils, medicinal plant extracts, and phyto-mediated bismuth nanoparticles demonstrated significant antibacterial and
antibiofilm activity against S. mutans and may serve as promising plant-based nanotherapeutic agents for pediatric
dental caries management.

Keywords: Dental caries, Streptococcus mutans, Biofilm, Nigella sativa, Piper betle, Bismuth oxide nanoparticles.