Abstract
Background: Reduction of the microbial load within the root canal system and intraradicular dentine to an acceptable level is crucial for successful endodontic therapy. Mechanical debridement significantly reduces the bacterial load, however, the adjunctive use of antimicrobial agents can further reduce the number of viable microorganisms. Currently used irrigants and medicaments have the potential to be cytotoxic by causing local tissue irritation or hypersensitivity. Antimicrobial peptides are polypeptides which can possess a broad-spectrum of antimicrobial activity providing a host defence system to combat infections whilst being minimally toxic to host cells. BM2 is a D-decameric cationic peptide. The antimicrobial potential of BM2 in a medium suitable for use as an intracanal medicament needs to be investigated.
Aim: The aim of the present study was to assess the in vitro antimicrobial efficacy of BM2 in an injectable polymer gel matrix against common endodontic pathogens.
Materials and Methods: Strains of Candida albicans, Streptococcus gordonii, Streptococcus mutans, and Enterococcus faecalis were grown from frozen glycerol stocks and confirmed. Dilutions of BM2 were prepared in aqueous solution and the minimum inhibitory concentration (MIC) determined using the broth microdilution assay. The minimum bactericidal/fungicidal concentration (MBC/MFC) was established by subculturing the broth dilution onto culture media. Poloxamer 407 (P407) gels, at 25% (w/v) were loaded with BM2 and the gel stability evaluated. The in vitro release profile of BM2 from the P407 formulations and the gel dissolution profile were obtained. The antimicrobial efficacy of BM2 in a P407 gel formulation was assessed on planktonic cell cultures and on 24 h monospecies biofilms using a crystal violet biofilm assay over 72 h. Comparisons were made between BM2 in aqueous solution, P407 gel alone, BM2 in P407 gel formulations, and saturated calcium hydroxide.
Results: Aqueous BM2 at 128 µg/mL completely inhibited the growth of all four strains after 24 h exposure. S. mutans NG8 was the most susceptible (MIC 4 µg/mL, MBC 8 µg/mL) while E. faecalis JH2-2 was the least susceptible (MIC 64 µg/mL). P407 gels containing BM2 were prepared with no marked alteration to the stability of P407. BM2 release increased with time and demonstrated a linear correlation with P407 dissolution. BM2 retained its antimicrobial activity when incorporated into P407 gels exhibiting bacteriostatic activity. S. mutans NG8 was the most susceptible to P407 with BM2 (MIC 32 µg/mL) while E. faecalis JH2-2 was the most resistant (MIC >512 µg/mL). The MIC values of BM2 in P407 were 8-fold higher than those required for aqueous BM2 and although higher concentrations were required, it demonstrated more sustained effects on cell cultures over 72 h. BM2 incorporated into P407 gels gave dose-dependent growth impairment and significantly disrupted biofilm detachment at 512 µg/mL. Saturated calcium hydroxide inhibited growth of the S. mutans 24 h biofilm, slowed growth of S. gordonii and C. albicans biofilms, but was ineffective against the E. faecalis biofilm.
Conclusions: BM2 in a P407 gel possesses antimicrobial activity against planktonic cultures and monospecies biofilms of C. albicans, S. gordonii, S. mutans and E. faecalis at concentrations 8-fold higher than that in solution. Antimicrobial activity was greater than saturated calcium hydroxide. Within the limitations of this study, BM2 in a polymer gel has demonstrated potential for use as an antimicrobial agent in the treatment of root canal infections.