Bacterial resistance following subgingival and systemic administration of minocycline.

The aim of the present study was to compare total numbers of cultivable bacteria and prevalence of resistance to minocycline among periodontal bacteria following subgingival or systemic application of minocycline in patients suffering from periodontal disease. 10 adult patients were administered 2% minocycline ointment subgingivally into their periodontal pockets at baseline, week 2 and months 1, 3, 6 and 9. Patients had scaling/root planing at baseline and month 6. In addition, 10 patients undergoing scaling/root planing followed by a 10-day course of systemic minocycline therapy, were studied and compared with the subgingival application group. Bacterial samples were taken from the 4 deepest pockets before each subgingival application of the drug. The systemic administration group was sampled at baseline and at week 2, as well as months 1 and 3 after completing the antibiotic treatment. For each patient at each sampling, bacterial samples were pooled, diluted, seeded on parallel blood agar plates and incubated aerobically and anerobically. After incubation, 30 colonies were picked at random and transferred to blood agar plates supplemented with 10 micrograms/ml minocycline, to estimate prevalence of minocycline-resistant bacteria. The results of this study indicate that subgingival application of minocycline ointment resulted in an initial reduction in total numbers of cultivable bacteria, which then remained depressed during the full year of the study. No such observation was made in the systemic administration. Both in the subgingival and the systemic administration group, the % of cultivable aerobic and anaerobic minocycline-resistant bacterial strains increased transiently following administration of the drug, but returned to baseline levels within 3 months post-treatment.(ABSTRACT TRUNCATED AT 250 WORDS)