Bacterial susceptibility to amoxicillin and potassium clavulanate in advanced periodontitis patients not responding to mechanical therapy.

Background, Aims: Between 4 and 8% of periodontitis patients are reported to respond poorly to conventional therapy. In these cases, adjunctive use of systemic antibiotics might be a reasonable therapeutic approach. The purpose of this study was to evaluate the effects of systemic amoxicillin/clavulanate as adjunct to periodontal surgery on the predominant subgingival microorganisms in patients not responding to mechanical therapy. Furthermore, the bacterial susceptibility to amoxicillin/clavulanate was analyzed before and after therapy in order to assess the clinical validity of pre-therapeutic susceptibility testing.
Methods: In 10 periodontitis subjects with no subgingival detection of Actinobacillus actinomycetemcomitans, the predominant subgingival organisms were identified using the identification system Rapid ID 32 A as well as antibiotic susceptibility was tested utilizing the E test.
Results: Porphyromonas gingivalis and Prevotella oralis were detected in 7/10 subjects and could no more recovered after therapy. Fusobacterium nucleatum and Peptostreptococcus micros were present in 5/10 patients before treatment, but could be detected in 6/10, resp. 3/10 after therapy. In 4/10 subjects harboring F. nucleatum and in 3/10 with P. micros, those organisms were not targeted by amoxicillin/clavulanate, although post-treatment testing revealed their alleged susceptibility (MICs varied from 0.023 to 0.032 microg/ml, resp. from 0.125 to 2.0 microg/ ml).
Conclusions: The results of this study suggest that the outcomes of conventional methods of susceptibility testing have to be interpreted very carefully when being used for treatment of plaque-related diseases. Furthermore, since the endpoint of systemic antibiotic treatment as adjunct to conventional therapy is elimination of F. nucleatum or P. micros in patients harboring these organisms, the use of amoxicillin/clavulanate appears not to be justified.