The novel spherical/rod-like silica nanoparticles-encapsulated pure chlorhexidine against oral microbes

Abstract

OBJECTIVES: Our recent study shows that the pure (freebase, non-salt form) Chlorhexidine (CHX) encapsulated in commercially available mesoporous silica nanoparticles (MSNs) is effective against oral bacterial biofilms (Seneviratne et al, 2014). We further tested the loading efficiency and release profile of CHX encapsulated in our newly synthesized two forms of spherical (S-MSNs) and rod-like MSNs (R-MSNs) (Li et al, 2014). This study investigated the antimicrobial effects of S-MSNs- and R-MSNs-encapsulated pure CHX on selected common oral microbes. METHODS: The minimum inhibitory concentrations (MIC) of S-MSNs- and R-MSNs-encapsulated pure CHX on Streptococcus sobrinus, Streptococcus mutans, Porphyromonas gingivalis and Candida albicans were determined using broth dilution method. Their time-dependent anti-bacterial effects on S. sobrius was evaluated by CFU counting, and their interactions were assessed by field emission scanning electron microscopy (FE-SEM). RESULTS: Overall, both S-MSNs- and R-MSNs-encapsulated pure CHX demonstrated potent antibacterial effects on S. sobrinus, S. mutans, P. gingivalis and C. albicans. The MICs of S-MSNs-encapsulated CHX against these microbes ranged from 3.31 (S. sobrinus) to 93.75 (C. albicans) µg/mL and 3.31 (P. gingivalis) to 125 (S. mutans) µg/mL at 24 h and 48 h, respectively. R-MSNs-encapsulated CHX exhibited higher MICs (27.08-325 µg/mL at 24 h and 27.08-650 µg/mL at 48 h) with reference to the S-MSNs CHX. S-MSNs-encapsulated CHX inhibited continuously on S. sobrius growth at a low saturated concentration through consistent release, during the 72 h experiment period as compared with the R-MSNs CHX (p<0.05). Notably, both forms of MSNs CHX attached on the bacterial surface with potential merge into the cells, while S-MSNs CHX could disperse more homogeneously with reference to R-MSNs CHX. CONCLUSIONS: This pioneering study suggests that the novel S-MSNs-encapsulated pure CHX may exhibit potent and long-lasting antimicrobial effects on these common oral microbes. Further investigation on the underlying mechanisms is highly warranted.