Effects of azithromycin, metronidazole, amoxicillin, and metronidazole plus amoxicillin on an in vitro polymicrobial subgingival biofilm model.

Chronic periodontitis is one of the most prevalent human diseases and is caused by dysbiosis of the subgingival microbiota. Treatment involves primarily mechanical disruption of subgingival biofilms and, in certain cases, adjunctive use of systemic antibiotic therapy. In vitro biofilm models have been developed to study antimicrobial agents targeting subgingival species. However, these models accommodate a limited number of taxa, lack reproducibility, and have low throughput. We aimed to develop an in vitro multispecies biofilm model that mimics subgingival plaque, to test antimicrobial agents. Biofilms were cultivated using the Calgary Biofilm Device and were exposed to amoxicillin (AMX), metronidazole (MTZ), azithromycin (AZM), and AMX-MTZ at four different concentrations for 12, 24, or 36 h. Chlorhexidine (CHX) (0.12%) was used as the positive control. The compositions of the biofilms were analyzed by checkerboard DNA-DNA hybridization, and the percent reduction in biofilm metabolic activity was determined using 2,3,5-triphenyltetrazolium chloride and spectrophotometry. Thirty-five of the 40 species used in the inoculum were consistently recovered from the resulting in vitro biofilms. After 36 h of exposure at the 1:27 dilution, AMX-MTZ reduced metabolic activity 11% less than CHX (q = 0.0207) but 54% more than AMX (q = 0.0031), 72% more than MTZ (q = 0.0031), and 67% more than AZM (q = 0.0008). Preliminary evidence of a synergistic interaction between AMX and MTZ was also observed. In summary, we developed reproducible biofilms with 35 subgingival bacterial species, and our results suggested that the combination of AMX and MTZ had greater antimicrobial effects on these in vitro multispecies biofilms than expected on the basis of the independent effects of the drugs.

Metronidazole alone or with amoxicillin as adjuncts to non-surgical treatment of chronic periodontitis: a secondary analysis of microbiological results from a randomized clinical trial.

AIM: To evaluate the changes occurring in the subgingival microbial profile of subjects with generalized chronic periodontitis (ChP) treated by scaling and root planing (SRP) alone or with metronidazole (MTZ) or MTZ + amoxicillin(AMX). A secondary aim was to examine a possible added effect of chlorhexidine(CHX) to these therapies. METHODS: One hundred and eighteen subjects were randomly assigned to receive SRP-only or with MTZ [400 mg/thrice a day (TID)] or MTZ + AMX (500 mg/TID) for 14 days. Half of the subjects in each group rinsed with 0.12% CHX twice a day (BID) for 2 months. Nine subgingival plaque samples/subject were analysed by checkerboard DNA­DNA hybridization for 40 bacterial species at baseline, 3, 6 and 12 months post-therapy. RESULTS: At 12 months, the antibiotic-treated groups harboured lower mean counts and proportions of key periodontal pathogens than the SRP group (p < 0.05). These benefits were observed at initially deep and shallow sites. Initial reductions in periodontal pathogens obtained with SRP partially rebound after 12 months. CHX rinsing enhanced the microbiological effects of the MTZ + AMX treatment in shallow sites. CONCLUSION: The adjunctive use of MTZ and MTZ + AMX results in a greater reduction in the levels of periodontal pathogens in generalized ChP subjects compared to SRP alone.