Enhanced antibacterial effect against Enterococcus faecalis by silver ions plus Triton X-100 with low concentrations and cytotoxicity

Abstract

Enterococcus faecalis (E. faecalis) is commonly considered to be one of chief culprits of secondary and persistent root canal infections. As antibiotic resistance has become a global issue, in order to reduce the use of antibiotics, metal ions have recently been widely used as an alternative. Silver ions (Ag⁺) have been proved to be a strong bactericide but with high cytotoxicity and discoloration property. Triton X-100 (TX-100) and Ag⁺ were co-used for the first time as a clinical intracanal medication to obtain both enhanced antibacterial effect and low cytotoxicity. The synergistic antibacterial effect of TX-100 + Ag⁺ was tested on both planktonic and biofilm-resident E. faecalis on dentine. And the cytotoxicity was tested on MC3T3-E1 cells. Results confirmed the antibacterial activity against both planktonic and biofilm-resident E. faecalis was dramatically improved after TX-100 incorporation. TX-100 and Ag⁺ mixture demonstrated a similar inhibitory effect as the 2% chlorhexidine (CHX), while the cytotoxicity was much lower than 2% CHX (p < 0.05). In conclusion, TX-100 + Ag⁺ mixture might be developed into a new effective intracanal medication as the 2% CHX.

Keywords: Antibacterial agent; Antimicrobial drug resistance; Enterococcus faecalis; Silver; Triton X-100.

Fig. 1

Antibacterial effects of different concentrations of TX-100 + Ag⁺ mixture against planktonic E. faecalis for 24 h (a–i) representative images of CFUs of 0.02% TX-100 + 25 μg/mL AgNO₃ group, 0.02% TX-100 + 50 μg/mL AgNO₃ group, 0.02% TX-100 + 75 μg/mL AgNO₃ group, 0.02% TX-100 + 100 μg/mL AgNO₃ group, 0.04% TX-100 + 25 μg/mL AgNO₃ group, 0.04% TX-100 + 50 μg/mL AgNO₃ group, 0.04% TX-100 + 75 μg/mL AgNO₃ group, 0.04% TX-100 + 100 μg/mL AgNO₃ group, and 2% CHX group. j Antibacterial efficiencies of different groups (*: significant difference when compared with 2% CHX group. #: significant difference when compared with BLK; p < 0.05)

Fig. 2

CCK-8 test on MC3T3-E1 osteoblastic cells (BLK, blank control group. *: significant difference when compared with 2% CHX group. #: significant difference when compared with BLK; p < 0.05)

Fig. 3

The antibacterial effect of TX-100 + AgNO₃ mixture against E. faecalis biofilms on dentin. a The OD value at 600 nm within 24 h after the direct soaking of dentin slices from different groups in fresh BHI media. b Comparisons of OD value at 600 nm at 24 h. c Representative images of CFUs of 0.02% TX-100 + 100 μg/mL AgNO₃(I), 0.04% TX-100 + 75 μg/mL AgNO₃(II), 0.04% TX-100 + 100 μg/mL AgNO₃(III), and 2% CHX group(IV) (*: significant difference when compared with 2% CHX group. #: significant difference when compared with BLK; p < 0.05)

Fig. 4

Representative FE-SEM images showing the inhibition of E. faecalis biofilms on dentin (a, b) biofilm treated with PBS (a × 5000; b × 20,000) (BLK); (c, d) biofilm treated with 100 μg/mL AgNO₃ only (c × 5000; d × 20,000); (e, f) biofilm treated with 0.04% TX-100 only (e × 5000; f × 20,000); (g, h) biofilm treated with 2% CHX only (g × 5000; h × 20,000); (i, j) biofilm treated with 0.02% TX-100 + 100 μg/mL AgNO₃ (i × 5000; j × 20,000); (k, l) biofilm treated with 0.04% TX-100 + 75 μg/mL AgNO₃ (k × 5000; l × 20,000); (m, n, o) biofilm treated with 0.04% TX-100 + 100 μg/mL AgNO₃ (m × 5000; n × 20,000; o × 50,000)