R.J. Gibbons

Dental caries and alveolar bone loss in gnotobiotic rats infected with capsule forming streptococci of human origin

Abstract Strains of streptococci have been isolated from each of three human carious lesions which proved cariogenic when tested in pure culture in gnotobiotic rats. The presence of two of these strains also resulted in extensive localized loss of alveolar bone. A streptococcus strain isolated from one of the human carious lesions studied was unable to induce caries in gnotobiotic rats. The biochemical and serological characteristics of these organisms indicate that the human cariogenic strains are similar to rodent cariogenic streptococci. Seven rodent and human cariogenic streptococci have been found to synthesize large quantities of extracellular non-dialysable capsule like carbohydrate from sucrose, while three strains of non-cariogenic streptococci formed lesser amounts, suggesting that capsule formation may be important in the caries process.

Synthesis of extracellular dextran by cariogenic bacteria and its presence in human dental plaque

Abstract The extracellular polysaccharide synthesized primarily from sucrose by certain human and rodent cariogenic bacteria has been found to be a dextran-like polymer. Maximum quantities of this polysaccharide were synthesized in 10% sucrose broth, and the presence of free glucose or fructose did not markedly repress synthesis of dextran from sucrose. The dextrans synthesized by rat, hamster, and human cariogenic streptococci, and by a cariogenic strain of Lactobacillus acidophilus proved immunologically similar. The extracellular dextran was found to be relatively resistant to attack by mixed oral bacterial growth; to form insoluble precipitates with serum, clarified saliva, and various protein solutions; and to adhere to powdered hydroxyapatite. Samples of pooled human dental plaque were found to contain a constituent which was immunologically similar to dextran, and which comprised almost 2% of its dry weight. It is proposed that dextran synthesis by cariogenic but not non-cariogenic bacteria, enables these organisms to form dental plaque which is required for the production of dental caries.

Bacterial Adherence and the Formation of Dental Plaques

The oral cavity contains a variety of types of surfaces which are colonized by bacteria; these include keratinized and non-keratinized mucosal surfaces and the teeth. In individuals with a healthy dentition, only the outer enamel layer covering the crowns of teeth is exposed to bacteria. However, in individuals with chronic periodontal disease, the alveolar bone which supports the teeth is progressively lost and apical migration of the gingiva occurs. This results in exposure of the cementum which covers the roots of the teeth.

Adherence as a determinant of the presence of Streptococcus salivarius and Streptococcus sanguis on the human tooth surface

The proportions of Streptococcus salivarius, and other zooglea-producing streptococci of the total facultative streptococci on Mitis-salivarius agar were determined in samples obtained from the lingual surfaces of both central upper incisors of nine subjects within 30–120 min after thorough prophylaxis. The percentages of Strep. salivarius on the tooth surfaces were much lower than those in samples of saliva or of the tongue tip obtained simultaneously. On the other hand, the percentages of other zooglea-forming streptococci, most of which were considered to be Streptococcus sanguis, were very high on the tooth surfaces but much lower in the saliva and tongue tip samples. The observed differences in proportions of these organisms in the initial phase of plaque formation are considered to be due to differences in ability to adhere to the tooth surface rather than in ability to grow on the tooth surface. These observations seem to provide an explanation for the relative proportions of Strep. salivarius and Strep. sanguis in mature dental plaque.

Adherence as an ecological determinant for streptococci in the human mouth

Abstract The adherence of Streptococcus species to dental plaque and oral epithelial surfaces was studied in vivo by introducing mixtures of streptomycin-labelled strains into the mouths of volunteers. The proportions of labelled Strep. sanguis recovered from the cleaned teeth or preformed plaques were much higher than those of Strep. salivarius after a 45 and 30 min experimental period respectively. The adherent behaviour of in vivo-grown labelled organisms for cleaned teeth was similar to that of the same species present naturally in the mouth. The data provide additional support for the concept that the low proportion of Strep. salivarius in dental plaque is due to its inability to adhere to the tooth surface or developing plaque. The proportions of labelled Strep. salivarius were higher than those of Strep. sanguis on the dorsum of the tongue but lower on the vestibular mucosa. The proportions of labelled Strep. mutans in both sites were low as compared to those of Strep. salivarius and Strep. sanguis. The relative adherence of these Streptococcus species to the tongue and vestibular mucosa correlates with their proportions found naturally in these sites. Thus, adherence seems to be an important determinant for the colonization of Strep. salivarius, Strep. sanguis and Strep. mutans on the tongue and vestibular mucosa as well as on teeth.

Studies of the predominant cultivable microbiota of dental plaque

Abstract All of the cultivable bacteria present in high dilutions of dental plaque have been isolated, partially characterized, and their relative proportions determined. The predominant cultivable microbiota of dental plaque was found to be comprised of the following groups of organisms: facultative streptococci, 27%; facultative diphtheroids, 23%; anaerobic diphtheroids, 18%; peptostreptococci, 13%; Veillonella , 6%; Bacteroides , 4%; fusobacteria, 4%; Neisseria , 3%; and vibrios, 2%. Total microscopic counts of dental plaque averaged 2·5 × 10 11 bacteria/g. Total cultivable counts performed anaerobically and aerobically averaged 4·6 and 2·5 × 10 10 /g respectively.

Studies of the predominant cultivable micro-organisms from the human tongue

Abstract The most numerous cultivable bacteria present on the dorsum of the tongues of six individuals were isolated and partially characterized. On the basis of 409 isolates examined, the tongue was found to contain a relatively constant microflora which was composed of the following microbial groups: facultative streptococci, 38.3 per cent; Veillonella, 14.5 per cent; facultative and anaerobic diphtheroids, 13.0 per cent and 7.4 per cent respectively; micrococci-staphylococci, 6.5 per cent; Bacteroides, 5.3 per cent; Peptostreptococcus-Peptococcus, 4.2 per cent; Neisseria, 2.3 per cent; vibrios, 2.1 per cent; Fusobacterium, 0.8 per cent; unidentified gram negative rods and cocci, 3.2 per cent and 2.6 per cent respectively. The recovery of total facultative streptococci, other than Streptococcus salivarius, was favoured by anaerobic incubation. The recovery of S. salivarius was either indifferent or slightly favoured by aerobic incubation.

Parameters that Effect the Adherence of Streptococcus salivarius to Oral Epithelial Surfaces

Different bacterial species are recognized to be localized within sites in the oral cavity,1q and several studies have shown that the ability of oral Streptococcus, Veillonella, and Neisseria species to adhere to various surfaces within the mouth correlates with their proportions found indigenously.4-7 Consequently, it appears that the relative ability of bacteria to become attached to oral surfaces influences the extent to which they colonize. Bacteria that are not attached to a surface are simply washed away by saliva and other fluids and swallowed. The adhesion between bacteria and either teeth or oral epithelial surfaces is surprisingly specific and evidently entails specific interactions among components present on the bacterial cell and components of the surface. The present study was initiated to determine whether the surfaces of oral epithelial cells and of bacteria could be modified in vitro by certain enzymes or bacterial polymers so as to alter their adherent interactions. Streptococcus salivarius was selected for study, since this organism is known to attach well to oral epithelial surfaces.6

Studies of the cultivable flora of normal human feces

Highly diluted feces, obtained from healthy adult individuals, was plated on blood-agar plates which were incubated both aerobically and anaerobically. From the anaerobic plates containing 30 to 60 colonies, every colony was subcultured. Nearly all isolates were obtained in pure culture and partially characterized. It was found thatBacteroides species were the most predominant organisms, being present in numbers approximating 1010 per gram wet weight. Selected bacteria present in lower numbers were determined by plating appropriate dilutions of feces on selective media. It was found that coliforms, streptococci and lactobacilli were regularly present in concentrations of 106 − 108 organisms per gram wet weight material, whileVeillonella, Streptococcus salivarius, Bacteroides melaninogenicus and staphylococci were present in lower numbers. Fusobacteria were only found in one sample, whileNeisseria were not detected in any of the samples. Wet mounts of fecal material, inspected by darkfield microscopy, did not reveal the presence of spirochetes.Anaerobes outnumbered facultative bacteria by a factor of 40, indicating that the human adult fecal flora is predominantly anaerobic. Total microscopic counts indicate that bacteria comprise approximately 30% of the mass of human feces.

Biochemical and immunological heterogeneity of Bacteroides melaninogenicus

Abstract A collection of fifty-one strains of Bacteroides melaninogenicus, representing isolates from the oral cavity, faeces, and pathologic lesions of humans, and strains from hamsters and a sheep, were compared in regard to carbohydrate fermentations and whole cell agglutination. The organisms were found to represent a heterogeneous group, both biochemically and serologically and no meaningful eco or serotypes could be delineated. Sheep erythrocytes sensitized with either lipopolysaccharides or soluble antigen extracts of the organism were used in haemagglu tination tests to detect the presence of circulating antibodies to B. melaninogenicus in normal human sera.