Strains of Streptococcus mutans of four genetic groups and five serotypes, and strains of S. sanguis, S. mitis, S. salivarius, Actinomyces naeslundii , and A. viscosus , were found to bind blood group-reactive (BGR) mucin isolated from whole human saliva. The bacteria studied bound mucins with blood type A or B reactivity to a similar extent, suggesting that the carbohydrate moieties responsible for the A and B antigenic determinants were not involved. The organisms studied appeared to bind different fractions of BGR mucin molecules because preparations absorbed with cells of a given oral species no longer contained BGR molecules which bound to homologous organisms but still possessed BGR components which bound to varying degrees to other bacteria. Differences were even noted among S. mutans strains belonging to different genetic groups and serological types. Immunoglobulins could not be detected in the mucin preparations, and addition of anti-human immunoglobulin A (IgA), IgG, or IgM serum to reaction mixtures did not affect binding. Mucin pretreated with periodate or iodoacetate no longer bound to S. mutans H12 cells, suggesting that carbohydrate moieties and sulfhydryl groups played an essential role. Active cell metabolism was not required for BGR mucin binding; however, pretreatment of H12 cells with periodate or heat (100°C for 15 min) reduced binding. Mucin labeled with [ 14 C]phenyl isothiocyanate appeared to bind to S. mutans H12 cells comparably to untreated mucin; the binding also appeared to be specific because less than 15% of the labeled material became bound when incubated with an excess of streptococci. Binding of [ 14 C]phenyl isothiocyanate-labeled mucin was not affected by neutral sugars tested or by preparations of c antigen, glycerol teichoic acid, dextran, or crude glucosyltransferase. However, binding was inhibited by several amines. BGR salivary mucins are present in the acquired pellicle covering teeth; the ability of bacteria to selectively bind such components suggest that they may serve as receptor molecules involved in the attachment of bacteria to teeth.

Adsorption of all of eight strains of Streptococcus mutans to saliva-treated hydroxyapatite (S-HA) surfaces was inhibited by galactose and melibiose, but not by other neutral sugars tested. This observation supports the hypothesis that lectin-like components participate in the attachment of these streptococci to salivary glycoproteins on saliva-treated hydroxyapatite surfaces. Adsorption of all strains was also inhibited by iodoacetate and spermine; other amines tested reduced adsorption of some strains, but not others.

The frequency of five Streptococcus mutans serotypes (a, b, c, d and e) was investigated in relation to tooth surface and its caries status in young schoolchildren. In the first study, plaque from the five surfaces of a second deciduous molar in 104 five-year-olds was examined for the presence of S. mutans. In the second study, isolations were made from the occlusals and approximal surfaces of a second deciduous and a first permanent molar in five- to eight-year-olds. The isolates were characterized biochemically, and then serotyped with antigen extracts against whole cell and ‘purified’ cell wall antisera using comparative immunoelectrophoresis. Of the 348 plaque isolates, type c was the prevalent serotype (91.1%). In the first study, a significant relation was found between the occurrence of type c and caries on the occlusal surfaces. However, the second study showed type c to be evenly distributed on the occlusals and approximal surfaces irrespective of caries status. This leaves open the possibility that certain types may be commensals.

Human strains of Actinomyces viscosus and A. naeslundii differ in the time of their appearance and in their patterns of colonization in the mouth. Strains of these organisms were found to differ in their abilities to adsorb to saliva-treated hydroxyapatite (S-HA) surfaces, thought to mimic the teeth, and these differences parallel their patterns of colonizing the dentition. Thus, strains of A. viscosus tended to adsorb in higher numbers to hydroxyapatite (HA) treated with saliva of older children and adults than with saliva of younger children (ages 6 to 11). These salivary changes may account for the increased frequency with which this organism can be isolated from the mouths of children as they grow older. In contrast, strains of A. naeslundii and Streptococcus mutans did not show a preference for attaching to either type of S-HA. Strains of A. viscosus also generally adsorbed in higher numbers than A. naeslundii to HA treated with adult saliva; this may explain why higher proportions of A. viscosus are usually recoverable from the teeth of adults, even though A. naeslundii is generally present in higher proportions in saliva. Significant variation was noted between strains and between saliva samples collected from different donors. The differences in adsorptive behavior of strains of these species suggests that they are binding to different receptors in the salivary glycoprotein coating on HA surfaces. Adsorption of A. naeslundii ATCC 12104 was enhanced when S-HA was pretreated with neuraminidase, but this had little effect upon the adsorption of other Actinomyces strains tested. Adsorption of strain ATCC 12104 to S-HA was also strongly inhibited by fructose and sucrose and weakly inhibited by glucose, maltose, galactose, and lactose. However, other strains of A. naeslundii tested were affected less, or not at all, by these sugars. Adsorption of two strains of A. viscosus was not affected by any of the sugars or amines tested.

The purpose of this study was to determine if populations of Streptococcus mutans which were undergoing antigenic variation while colonizing gnotobiotic rats concomitantly became altered in physiological characteristics which affected their virulence. S. mutans strain JBP (serotype c), which was freshly isolated from a carious lesion in a 6-year old child, was used to inoculate gnotobiotic rats; uninfected animals served as controls. Substrains were isolated from animals 1, 2, 3, 4, and 12 weeks after infection; samples of pilocarpine-stimulated saliva were also obtained from representative animals for antibody analyses. Isolates derived from stock cultures of strain JBP proved to be homogeneous with respect to all of the physiological characteristics monitored. However, substrains isolated from the animals within 4 weeks after infection were altered with respect to their ability to agglutinate in the presence of sucrose, their ability to form adherent growth in sucrose broth, and the terminal pH attained in glucose broth. Some isolates obtained 12 weeks after infection no longer synthesized detectable levels of c antigen or intracellular glycogen, and they formed atypical smooth colonies on mitis salivarius agar. With an enzyme-linked immunosorbent assay, low levels of immunoglobulin A (IgA) antibodies reactive with whole JBP cells were detected in saliva samples of uninfected control animals at each sampling period; these evidently were induced to antigens contained in the diet of the animals. Significantly higher levels of IgA antibodies were present in saliva samples from animals infected with strain JBP for 3 weeks or longer. Thus, the emergence of antigenic and physiological variants of S. mutans in the animals was paralleled by increased levels of salivary IgA antibodies. The reactivity of salivary IgG with JBP cells was low, and it fluctuated in both groups of animals. No antibodies of the IgM class were detected. When tested in gnotobiotic rats, several variants, including strains which no longer formed typical rough colonies or adherent growth in sucrose broth, proved much less virulent than parental strain JBP in inducing carious lesions. Prior oral immunization, which resulted in higher levels of salivary and serum IgA antibodies reactive with strain JBP, was found to accelerate the emergence of smooth-colony variants in the animals; it was also associated with decreased streptococcal population levels on the teeth and in feces of the rats. It is suggested that part of the mechanism by which artificial immunization leads to a reduction in dental caries development in experimental animals is due to the earlier selection of less virulent streptococcal populations.