The predominant cultivable flora of tooth surface plaque removed from institutionalized subjects

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Tooth surface plaque was removed from 11 institutionalized individuals and cultured on agar plates in an anaerobic chamber. The recovery of organisms on a dilute trypticase yeast extract medium (MM10), incubated anaerobically, averaged 33 ± 26 per cent of the microscopic count. Growth on MM10, under aerobic conditions averaged 8 ± 5 per cent. The anaerobe to aerobe recovery ratio on medium MM10 was about 4. Six hundred and seventy-one isolates grew on subculture and were partially characterized. About half the isolates were not capable of lowering the pH in glucose broth below 5·5. Streptococci accounted for about 38 per cent of the isolates and were found in each subject. A sub-group of 15 strains grew in 40 per cent bile, formed NH 3 from arginine, fermented salicin, but not inulin. These isolates possessed characteristics of Streptococcus sanguis and Streptococcus mitis. Various Actinomyces species comprised about 14 per cent and Clostridium species accounted for 8 per cent of the cultivable flora. Bacteroides melaninogenicus, Fusobacterium species, and Veillonella species each were about 6 per cent of the isolates. The overall character of these plaque isolates suggested that a gingival crevice microflora containing several amino-acid fermenting species had colonized the tooth surfaces. These organisms would not be expected to produce a plaque capable of decalcifying enamel, which might explain why these subjects had a low caries experience.