Doxycycline-resistant bacteria in periodontally diseased individuals after systemic doxycycline therapy and in healthy individuals.
The occurrence of doxycycline-resistant bacteria was examined in subgingival plaque and on the tonsils of 12 periodontally healthy and 12 periodontally diseased individuals. The healthy group was examined 6 times at intervals of one month. The diseased group was examined before and 1, 5, 15, 26, 39, and 52 weeks after conventional periodontal therapy supplemented with systemic doxycycline for 3 weeks. The occurrence of doxycycline-resistant bacteria in the healthy group varied on average between 2.0% and 6.6% in subgingival plaque and between 3.0% and 12.4% in the tonsil samples over a 6-month period. In the diseased group the percentage of resistant bacteria increased from 10-20 times for tonsil and subgingival plaque, respectively. About half a year after therapy the values returned to the baselines. For both groups the morphological distributions of resistant bacteria were similar and unaffected by the doxycycline therapy.