Cell-to-cell interactions are essential for the formation of dental plaque. A continuous layer of Streptococcus sanguis SA-1 cells fixed to a solid surface has been used to evaluate interactions among this bacterium, Haemophilus parainfluenzae, and Streptococcus sobrinus. S. sanguis cells were attached to a Falcon 3001 tissue culture plates or bovine enamel chips, coated with a biological adhesive. Scanning electron microscopy of the chips showed the streptococci as a contiguous surface. Radiolabeled bacteria were used to measure a second-species interbacterial adherence to the streptococcal-coated culture plates. Strains of H. parainfluenzae known to coaggregate (strain HP-28) and not to coaggregate (strains HP-42 and HP-80), in suspension with S. sanguis strain SA-1, were studied for adherence. Ten-fold-higher numbers of coaggregating strain HP-28 adhered in vitro to the streptococcal layer than did the non-coaggregating strains. S. sobrinus strain 6715 did not show appreciable adherence to the S. sanguis surface. Saliva did not affect the adherence of coaggregating or non-coaggregating H. parainfluenzae strains to S. sanguis strain SA-1. Bovine enamel chips, coated with streptococci, mounted on modified orthodontic appliances and placed in the mouths of three volunteers, facilitated the measurement of interbacterial adherence in vivo of streptomycin-resistant strains of H. parainfluenzae (HP-28R or HP-42R). Suspensions of bacteria were placed into the mouth, distributed throughout, and expectorated. After 15 or 120 minutes, the appliance with the chips was removed, the chips sonified, and colony-forming units (CFU) of streptomycin-resistant haemophili determined per chip.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuraminidase-sensitive adherence to experimental salivary pellicles was studied using eight strains of Streptococcus sanguis and five strains of Streptococcus mitis. Approximately 60% of the strains of each species showed significantly lower adherence to neuraminidase-treated versus untreated saliva-coated hydroxyapatite. In addition, the adherence of several of these streptococcal strains to saliva-coated hydroxyapatite and neuraminidase-treated saliva-coated hydroxyapatite was inhibited using galactose and N-acetyl-D-galactosamine. Results from these studies suggested that several salivary receptors mediate adherence of these species.

Eight human subjects with healthy oral conditions were examined to study developing dental plaque. Supragingival plaque, buccal mucosa, tongue dorsum and saliva were sampled prior to the pumicing and cleaning of facial surfaces of the four upper premolars and two first molars. Samples were processed anaerobically on media that were selective for the oral Streptococcus spp., Haemophilus spp., and Actinomyces spp., as well as supplemented blood agar for identification of gram-negative bacterial groups and total cultivable flora. NAD-requiring Haemophilus spp., Streptococcus sanguis, Streptococcus mitis, Streptococcus mutans and Streptococcus salivarius were found in most oral samples. Analysis of the distribution of the Actinomyces spp., Actinomyces viscosus, Actinomyces naeslundii and Actinomyces odontolyticus in oral samples prior to teeth cleaning, found no significant differences between proportions or prevalence of these species in saliva, buccal mucosa, tongue, or pooled plaque samples. All three species were found on most surfaces in all subjects. Following cleaning, plaque was allowed to develop for 48 h. Proportions of a species in 2-hour plaque, when higher than proportions in the same individual’s saliva samples, were interpreted to be due to a species promotion by salivary pellicle (as 2-hour plaque from cleaned teeth). A median ratio of 1:3 of saliva versus 2-hour plaque was seen for A. odontolyticus suggesting some promotion by pellicle. A. viscosus and S. sanguis showed median ratios of saliva:2-hour plaque of 1:6 or higher, suggesting that salivary pellicle strongly promoted these species’ adherence. Developing plaques contained high proportions of streptococci, especially S. sanguis and S. mitis, as well as Haemophilus parainfluenzae. Significant increases were seen in proportions of S. sanguis in 48-hour versus 24-hour, and 2-hour plaques. A. viscosus, A. naeslundii and A. odontolyticus were found in most developing plaque samples and in similar proportions to each other. A significant twofold increase in proportions of A. odontolyticus, and fourfold increase of S. sanguis, was seen in 48- versus 2-hour plaques suggesting growth of these species. Forty-eight-hour plaque was composed primarily of Facklam type 1 S. sanguis and this species was found in significantly higher proportions than S. salivarius or S. mutans. NAD-requiring haemophili were found in high proportions and comprised 99% of the haemophili in 48-hour plaque. Although A. naeslundii was not dectected in as many 48-hour samples as A. viscosus or A. odontolyticus, these three species were found in similar proportions in 48-hour developing plaque samples.