Change in subgingival microbial profiles in adult periodontitis subjects receiving either systemically-administered amoxicillin or metronidazole

Aim: The current investigation evaluated changes in levels and proportions of 40 bacterial species in subgingival plaque samples during, immediately a fter and up to 1 year after metronidazole or amoxicillin therapy combined w ith SRP. Method: After baseline clinical and microbiological monitoring, 17 adult pe riodontitis subjects received full mouth SRP and 14 days systemic administr ation of either metronidazole (250 mg, TID, n=8) or amoxicillin (500 mg, TI D n=9). Clinical measurements including % of sites with plaque, gingival re dness, bleeding on probing and suppuration, pocket depth (PD) and attachmen t level (AL) were made at baseline, 90, 180 and 360 days. Subgingival plaqu e samples were taken from the mesial surface of all teeth in each subject a t baseline, 90, 180 and 360 days and from 2 randomly selected posterior tee th at 3, 7, and 14 days during and after antibiotic administration. Counts of 40 subgingival species were determined using checkerboard DNA-DNA hybrid ization. Significance of differences over time was determined using the Qua de test and between groups using ANCOVA. Results: Mean PD was reduced from 3.22 +/-0.12 at baseline to 2.81 +/-0.16 (p <0.01) at 360 days and from 3.38 +/-0.23 mm to 2.80 +/-0.14 mm (p <0.01) in the amoxicillin and metronidazole treated subjects respectively. Corres ponding values for mean AL were 3.21 +/-0.30 to 2.76 +/-0.32 (p <0.05) and 3.23 +/-0.28 mm to 2.94 +/-0.23 mm (p <0.01). Levels and proportions of Bac teroides forsythus, Porphyromonas gingivalis and Treponema denticola were m arkedly reduced during antibiotic administration and were lower than baseli ne levels at 360 days. Counts (x10(5), +/- SEM) of B. forsythus fell from b aseline levels of 0.66 +/-0.16 to 0.04 +/-0.02, 0.13 +/-0.04, 0.10 +/-0.03 and 0.42 +/-0.19 in the amoxicillin group at 14, 90, 180 and 360 days respe ctively (p <0.001). Corresponding values for metronidazole treated subjects were: 1.69 +/-0.28 to 0.02 +/-0.01, 0.20 +/-0.08, 0.22 +/-0.06 and 0.22 +/ -0.08 (p <0.001). Counts of Campylobacter species, Eubacterium nodatum, Fus obacterium nucleatum subspecies, F, periodonticum and Prevotella nigrescens were also detected at lower mean levels during and immediately after thera py, but gradually increased after withdrawal of the antibiotics. Members of the genera Actinomyces Streptococcus and Capnocytophaga were minimally aff ected by metronidazole. However, amoxicillin decreased the counts and propo rtions of Actinomyces species during and after therapy. Conclusions: The data suggest that metronidazole and amoxicillin are useful in rapidly lowering counts of putative periodontal pathogens, but must be accompanied by other procedures to bring about periodontal stability.