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The search for novel antimicrobial agents in Endodontics is constant to overcoming persistent infections. L. is a medicinal plant little explored in Endodontics. The aim of this study was to produce hydroethanolic extract of L. and to evaluate its phytochemical composition, antimicrobial and antibiofilm action against standard and clinical strains of and , and cytotoxicity and genotoxicity on human keratinocyte cultures (HaCaT cells). The findings provide new insights into the potential of as an alternative endodontic antimicrobial agent, contributing to the development of more effective and biocompatible therapeutic strategies. hydroethanolic extract was produced using young leaves of guajava and extracted using absolute ethanol and ultrapure water in a ratio (30 g:100 mL). The solid soluble, total flavonoid and total phenols content were determined. The chemical composition was determined high-performance liquid chromatography (HPLC) analysis, then the free radical suppressive activity was assessed by determining the IC value, indicating the concentration required to eliminate 50% of free radicals. Later, the minimum inhibitory concentration (MIC) and minimum microbicidal concentration (MMC) of the extract was evaluated against the strains using clinical and laboratory standards institute (CLSI) guidelines (M27-S4 and M7-A9). Then, the antibiofilm activity was evaluated MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. Finally, the cytotoxicity of the extract was evaluated Alamar Blue assay, and the genotoxicity micronucleus assay on human keratinocyte cultures (HaCaT cells). Data were analyzed using ANOVA and Tukey's test or Kruskal-Wallis and Dunn's test. The soluble solids content in the extract was 3.35%. Using the quercetin standard curve, the total flavonoid concentration was 0.130 ± 0.110 mg/mL. In addition, using standard curve for phenolic acids, the total phenolic concentration was 1.770 ± 1.540 mg/mL. HPLC analysis revealed peaks of rutin, quercetin and kaempferol as major flavonoids in the L. extract. The extract demonstrated notable antioxidant activity, with an IC value of 10.39 µg/mL. The MMC values ranged 1.04-8.37 mg/mL. The extract at 8.37 mg/mL was effective in reducing the biofilms of standard and clinical strains of and after 10 min. Cytotoxicity analysis revealed that all tested concentrations exhibited relatively low toxicity toward HaCaT cells. Genotoxicity assessment the micronucleus assay indicated minimal DNA damage at all tested concentrations. Overall, L. hydroethanolic extract at 8.37 mg/mL is the most effective concentration in reducing the biofilm of the standard and clinical strains of and , while maintaining biocompatibility with HaCaT cultures.

Enterococcus faecalis is strongly associated with secondary/persistent root canal infections, being the most prevalent bacterium in cases of apical periodontitis in previously treated teeth. This study was elaborated to evaluate the anti-planktonic, antibiofilm, and synergistic effects of Nasturtium officinale and Psidium guajava hydroethanolic extracts against standard and clinical strains of E. faecalis. Firstly, the N. officinale extract was prepared from watercress leaves, and P. guajava extract was prepared from guava tree leaf shoots. Then, the content of soluble solids was quantified in both. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the isolated N. officinale and P. guajava extracts for each bacterial strain were determined using the broth microdilution method, following the Clinical and Laboratory Standards Institute (CLSI) guideline M7-A9. The MTT assay was used to evaluate the antibiofilm activity, and the fractional bactericidal concentration index (FBCI) was utilized to evaluate the synergistic effect of the N. officinale and P. guajava extracts using the checkerboard technique. Again, the MTT assay was used to evaluate the antibiofilm activity of the combined extracts this time. The data were subjected to statistical analysis using ANOVA and Tukey’s test, with a significance level of p ≤ 0.05. It was found that the soluble solid content of N. officinale was 50 mg/mL, and of P. guajava was 33.5 mg/mL. The MBC value of N. officinale was 12.5 mg/mL, and of P. guajava was 0.52 mg/mL against all the tested strains of E. faecalis. The combined 0.1 mg/mL N. officinale + 0.1 mg/mL P. guajava, and 0.1 mg/mL N. officinale + 0.5 mg/mL P. guajava hydroethanolic extracts effectively reduced the biofilm formation of the standard and clinical strain 4 of E. faecalis. Therefore, these combined extracts may be considered as endodontic irrigants in future studies.