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 after and up to 1 year after metronidazole or amoxicillin therapy combined with SRP. Method: After baseline clinical and microbiological monitoring, 17 adult periodontitis subjects received full mouth SRP and 14 days systemic administration of either metronidazole (250 mg, TID, n=8) or amoxicillin (500 mg, TID n=9). Clinical measurements including % of sites with plaque, gingival redness, bleeding on probing and suppuration, pocket depth (PD) and attachment level (AL) were made at baseline, 90, 180 and 360 days. Subgingival plaque samples were taken from the mesial surface of all teeth in each subject at baseline, 90, 180 and 360 days and from 2 randomly selected posterior teeth at 3, 7, and 14 days during and after antibiotic administration. Counts of 40 subgingival species were determined using checkerboard DNA-DNA hybridization. Significance of differences over time was determined using the Quade 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. Corresponding 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 Bacteroides forsythus, Porphyromonas gingivalis and Treponema denticola were markedly reduced during antibiotic administration and were lower than baseline levels at 360 days. Counts (x10(5), +/- SEM) of B. forsythus fell from baseline 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 respectively (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, Fusobacterium nucleatum subspecies, F, periodonticum and Prevotella nigrescens were also detected at lower mean levels during and immediately after therapy, but gradually increased after withdrawal of the antibiotics. Members of the genera Actinomyces Streptococcus and Capnocytophaga were minimally affected by metronidazole. However, amoxicillin decreased the counts and proportions 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.