Effect of antibiotics on ex vivo biofilms from residual sites

Objectives: To characterize the microbiota of residual periodontal sites of individuals with severe periodontitis 6 months after periodontal therapy, and to test the effect of different antibiotics to change the biofilm profile of these sites, using ex vivo biofilms.
Methods: Volunteers with severe periodontitis received scaling and root planning, 400 mg of Metronizadol (MTZ) and 500 mg of Amoxicillin (AMX), TID for 14 days. Follow-up after 3 and 6 months of treatment was performed. Biofilm samples from residual sites (probing depth ≥5 mm) at 6 months were collected and grown on ex-vivo biofilms under anaerobiosis. After 10 days, biofilms were exposed to AMX + Potassium Clavulanate (AMX+CLA), MTX+AMX or MTZ. The microbial compositions of the biofilms were determined by checkerboard DNA-DNA hybridization. Significant differences were determined by Friedman and Kruskall-Wallis tests.
Results: Four volunteers were included, 16 sites analyzed and 384 ex vivo biofilms grown. Significant clinical improvements were observed in all clinical parameters after 6 months. One patient remained with high risk and three achieved a moderate risk for disease progression. Significant beneficial changes on biofilm microbial profiles were observed after six months (p< 0.05). However, the microbial profile of residual sites still showed high levels of orange and red complexes. MTZ and MTZ+AMX were more effective in increasing the mean counts of Actimonomyces sp. cells than AMX+CLA, from 5.4x10⁴ to 27x10⁴, to 27x10⁴ and to 2.4x10⁴, respectively (p<0,05). AMX+CLA reduced better the mean counts of red complex species cells than MTZ and MTZ+AMX (p<0.05).
Conclusions: Residual periodontal sites show a microbiota compatible with active periodontitis. AMX+CLA was the most effective combination to reduce periodontal pathogens species on ex vivo biofilms.