The effect of metronidazole plus amoxicillin or metronidazole plus penicillin V on a periodontal biofilm model. An in vitro study.

Background: Antibiotic resistance has become life-threatening. A combination of metronidazole and amoxicillin is commonly used as adjunct to periodontal therapy. The aim of this study was to utilize an in vitro biofilm model to test the effect of replacing the broad-spectrum amoxicillin with penicillin V in the combination with metronidazole. Methods: An in vitro biofilm model, consisting of Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis and Fusobacterium nucleatum was developed. Biofilms were exposed to chlorhexidine digluconate (CHX) 0.2%, as positive control, and either to metronidazole/amoxicillin or metronidazole/penicillin V in two different concentrations. Statistical significance was achieved if p < 0.05 with paired t-test. Results: There was no growth of any bacterial species after 2h exposure to 0.2% CHX. Together, the two combinations of antibiotics were effective against F. nucleatum and P. gingivalis, but less effective against A. actinomycetemcomitans. No significant difference was found between the two combinations of antibiotics to combat A. actinomycetemcomitans neither in high (p = 0.95) nor in low concentration (p = 0.17). Conclusion: A combination of metronidazole with penicillin V had similar inhibiting effect as metronidazole combined with amoxicillin on an in vitro three-species biofilm model. Use of a narrow spectrum antibiotic may be indicated in combination with metronidazole.