Breaking the biofilm barrier: herbomineral nanocomposites to control Staphylococcus epidermidis through oxidative response and biofilm disruption.

The growing prevalence of antibiotic resistance and biofilm-forming dental pathogens necessitates the development of alternative antimicrobial strategies. Staphylococcus epidermidis is an opportunistic pathogen associated with dental biofilms, oral microbial colonization, and implant-related infections, contributing to persistent infections and treatment challenges. In this study, a herbomineral nanocomposite (HMNCs) was fabricated using the traditional Siddha formulation Kalnar Parpam and silver nitrate, and its antibacterial and antibiofilm activities were evaluated against S. epidermidis isolates obtained from dental caries-associated samples. Physicochemical characterization supported the formation of HMNCs. UV-Vis spectroscopy showed a characteristic surface plasmon resonance peak around 400 nm, while FTIR analysis revealed functional groups associated with the mineral matrix and synthesized HMNCs. XRD confirmed the crystalline nature of the material, and FESEM showed clustered nanostructures with particle sizes ranging from 52.8 to 117.9 nm, with an average particle size of 70.15 nm. DLS showed a hydrodynamic diameter of 400.4 nm with a polydispersity index of 0.197, while the zeta potential was -3.7 mV. XPS confirmed the presence of silver on the HMNCs surface, and ICP-OES quantified the total silver content as 0.040 mg/g (40 μg/g). TGA showed an approximately 18% mass loss up to 800 °C, with substantial inorganic residue. HMNCs exhibited antibacterial activity, with MIC values ranging from 0.325 to 1.5 μg/mL and MBC values ranging from 0.325 to 3.125 μg/mL. The MBC/MIC ratios ranged from 1.00 to 2.15 based on the operational MBC endpoint used in this study. Resazurin assays demonstrated concentration-dependent suppression of bacterial metabolic activity. HMNCs exposure was associated with increased DCFDA fluorescence and MDA levels, together with changes in GSH, SOD, and CAT parameters and leakage of intracellular sugars, proteins and nucleic acids. Furthermore, HMNCs inhibited biofilm formation and reduced preformed biofilm biomass, as demonstrated by crystal violet staining, with complementary FESEM and CLSM analyses using the SE4 isolate. Overall, the findings provide preliminary in vitro evidence of the antibacterial and antibiofilm activity of HMNCs and support further investigation of this Siddha-inspired nanomaterial for potential oral healthcare applications.