The predominant cultivable subgingival flora of beagle dogs following ligature placement and metronidazole therapy

Ligature-induced periodontitis was evaluated microbiologically in 8 beagle dogs. Gingival health was established by repeated cleaning. At day 0 subgingival plaque was sampled from individual sites in two quadrants. All teeth in one quadrant were then ligated at the CEJ, and the other quadrant served as a non-ligated control which was cleaned three times each week. At day 14, four dogs were given metronidazole for seven days. Plaque was cultured anaerobically on nonselcctive media, and the predominant cultivable flora was characterized. At day 0 Gram-negative facultative rods represented 56.8 % of the flora. with motile and surface translocating organisms predominating. At day 14 Bacteroides asaccharolyticus , including catalase positive B.asaccharolyticus-like organisms, increased at ligated sites to 34.7 % of the cultivable flora. After metronidazole therapy the total bacterial count decreased, and Gram-negative anaerobic rods became non-detectable. Gram negative facultative bacteria which were motile or surface translocating represented 52.7 % of the cultivable flora after metronidazole treatment.
In the beagle dog ligature placement was associated with a shift in the flora from Gram-negative facultative rods to Gram-negative anaerobic rods. Metronidazole treatment reduced the total cultivable flora and selectively reversed the microflora shifts which followed ligature placement.