[In vitro study of antimicrobial efficacy of different irrigations on Enterococcus faecalis biofilm formation in root canal].

PURPOSE: To compare the antimicrobial effect of different irrigations on Enterococcus faecalis biofilms in extracted teeth and evaluate the antimicrobial activity of irrigating solutions residual against E. faecalis biofilms formation, in order to provide a better strategy for clinician. METHODS: Extracted human premolar teeth with single root canal were clearly autoclaved. These teeth were contaminated with E. faecalis（ATCC33186） and incubated for 60 days. The samples were randomly assigned to 4 experimental groups. During biomechanical instrumentation, the root canal was irrigated with different irrigating agents. The bacteria samples were collected with sterile paper points before and after instrumentation to F2. Then, samples that had been instrumented and autoclaved again were randomly divided into 2 groups treated with normal saline and 1%NaOCl for 30 min. E. faecalis was used to contaminate these root canals. The bacteria samples were collected with sterile paper points after 2, 6, 24, 48 h. SPSS19.0 software package was used for statistical analysis. RESULTS: Group using 1% NaOCI with ultrasound devices was significantly more effective than NS alone groups. 1% NaOCI groups showed a better residual activity than NS group. CONCLUSIONS: NaOCl is still the most important irrigating solutions, and it could be a better choice after biomechanical instrumentation, because of its long time substantivity achieves residual antimicrobial activity. Ultrasound devices is recommended to coordinate with irrigation.

[Effect of different stress conditions on growth and biofilm formation capability of Enterococcus faecalis].

OBJECTIVE: To study the changes of growth and biofilm formation capability of Enterococcus faecalis (Ef) in different stress conditions. METHODS: The changes of growth of Ef in stress conditions were observed by measuring the A600 value with ultraviolet spectrophotometer. Ef was incubated on glass slide in stress conditions, biofilm formation capability of cells was investigated by colony-forming unit (CFU) counting of the culturable bacteria and fluorescence confocal laser scanning microscopy. RESULTS: Ef couldn't growth under the conditions of 2%, 5%NaClO, pH = 11 and 12, the A600 value was unchanged in 96 hours. But the growth curve changed at different levels in other stress conditions: under 1%NaClO, the A600 value peaked at 1.461 at 16 hour (the peaked level was 1.238 at 6 hours in control group) ; under 0,0.05%,0.15% glucose, it peaked at 0.645,0.890, 1.173, respectively, at 6 hour (it was maximized to 1.195 at 6 hours in control group); the A600 value peaked at 1.704 at 6 hours at pH = 9 and 1.225 at 10 hours at pH = 10 (the peak level was 1.732 at 6 hours at pH = 7) . Biofilm assay showed that Ef were able to form biofilm in these stress conditions except 5%NaClO and pH = 12. CONCLUSIONS: Ef could growth and form biofilms in energy starvation, low concentrations of sodium hypochlorite and weak alkaline stress.