since improvement of the periodontal condition is clearly associated with the subgingival elimination of a actinomycetemcomitans minocycline was found to be inactive in eliminating a actinomycetemcomitans from the subgingival area the above results are also in agreement with previous studies in which it was shown that tetracyclines were not successful in suppressing a actinomycetemcomitans in ljp patients and that further periodontal destruction is associated with continued presence of a actinomycetemcomitans in patient c a significant reduction in the number of a actinomycetemcomitans was obtained with the surgical treatment however the improved clinical situation of patient c appeared to be not stable after the surgery this was strongly associated with the outgrowth of a actinomycetemcomitans from these data one may conclude that even 37 cfu colony forming units recovered of this microorganism in the subgingival area is too many and may lead to further periodontal inflammation and periodontal breakdown the combination of metronidazole plus amoxicillin appeared to be very active against subgingivally occurring a actinomycetemcomitans since eradication below detection level of this bacterium was achieved in all four patients repeated microbiological examinations in the patients of the present study has revealed no reinfection of the subgingival area as control to the claims of synergistic action for amoxicillin and metronidazole data were obtained for 10 a actinomycetemcomitans positive adult periodontitis.