Effect of the Combinatorial Use of Naringin and Silver Nanoparticles on Enterococcus Faecalis

The combination of flavanones with silver nanoparticles (AgNPs) may combat Enterococcus faecalis (E. faecalis), hence mitigating damage to periapical tissues during endodontic procedures.

The aim of this research was to evaluate the antibacterial activity of naringin and its aglycone derivatives, both alone and in combination with silver nanoparticles, against E. faecalis, as well as the effects on bacterial morphology and genes associated with virulence.

We examined the antimicrobial activities of naringin and its derivatives individually and in combination with silver nanoparticles by measuring the minimal inhibitory concentration (MIC) and combinatorial effect using a checkerboard assay. We assessed the efficacy of irrigation in an ex vivo model using human teeth. We conducted gene expression analysis of virulence-associated genes using the qPCR technique. A scanning electron microscope (SEM) was used to examine morphological changes in Enterococcus faecalis following exposure to the tested compounds.

Naringin and its derivatives (prunin and naringenin) demonstrated 50% growth inhibition of E. faecalis at concentrations exceeding 21,500 μg/mL. Combining naringin with AgNPs failed to improve its antimicrobial properties but disrupted the typical pairs (diplococci) and the organizational structure, showing greater bacterial aggregation. This study is the first to report indicating that antimicrobial concentrations of naringin and its derivatives upregulate the expression of genes related to stress protection mechanisms and biofilm formation.

The results suggest that naringin could enhance the tolerance of E. faecalis to stressful conditions, impacting the potentiated antibacterial effect of conjugated AgNPs. The impact on biofilm warrants further investigation.