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

Sunnnary-Tooth surface plaque was removed from 11 institutional~ed individuats and cultured on agar plates in an anaerobic chamber. The recovery of organisms on a dilute trypticase yeast extract medium (MMIO), incubated anaerobically, averaged 33 & 26 per cent of the microscopic count. Growth on MMlO, under aerobicconditions averaged 8 i: 5 per cent. The anaerobe to aerobe recovery ratio on medium MM10 was about 4. Six hundred and seventy-one isoiates 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 NH3 from arginine, fermented salicin, but not inulin. These isolates possessed characteristics of Streptococcus sang& and Streptococcus mitis. Various Actinomyces species comprised about 14 per cent and Clo~tr~iam 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.