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 t o respond poorly to conventional therapy. In these cases, adjunctive use of systemic antibiotics might be a reasonable therapeutic approach. The purpo se of this study was to evaluate the effects of systemic amoxicillin/clavul anate as adjunct to periodontal surgery on the predominant subgingival micr oorganisms in patients not responding to mechanical therapy. Furthermore, t he bacterial susceptibility to amoxicillin/clavulanate was analyzed before and after therapy in older to assess the clinical validity of pre-therapeut ic susceptibility testing. Methods: In 10 periodontitis subjects with no subgingival detection of Acti nobacillus actinomycetemcomitans, the predominant subgingival organisms wer e identified using the identification system Rapid ID 32 A as well as antib iotic 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 nuclea tum and Peptostreptococcus micros were present in 5/10 patients before trea tment, but could be detected in 6/10, resp. 3/10 after therapy. In 4/10 sub jects harboring F. nucleatum and in 3/10 with P. micros, those organisms we re not targeted by amoxicillin/clavulanate, although post-treatment testing revealed their alleged susceptibility (MICs varied from 0.023 to 0.032 mu g/ml, resp. from 0.125 to 2.0 mu g/ml). Conclusions: The results of this study suggest that the outcomes of convent ional methods of susceptibility testing have to be interpreted very careful ly when being used for treatment of plaque-related diseases. Furthermore, s ince the end point of systemic antibiotic treatment as adjunct to conventio nal therapy is elimination of F. nucleatum or P. micros in patients harbori ng these organisms, the use of amoxicillin/clavulanate appears not to be ju stified.