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The ecology and identity of IgAl protease-producing streptococci in the human oral cavity were studied in an attempt to obtain insight into the significance of IgAl proteases for host - parasite relationships. Contrary to previous observations, a detailed taxonomic analysis of oral streptococci revealed that all strains of S. sanguis and S. Oralis ("S. mitior") produced IgAl protease. In addition, IgAl protease activity was observed in some isolates of S. Mitis. Of the streptococci that initiate plaque formation on dental enamel 88% (median value) had IgAl protease activity. Low proportions of the streptococci that colonize the tongue and oro-pharyngeal mucosae produced IgAl protease, in contrast to 60% of streptococci isolated from buccal mucosa. The IgAl proteases from S. Sanguis I-III, S. Sanguis IV, S. Oralis, and S. Mitis were distinct as revealed by studies using enzyme-neutralizing antibodies.

This study describes the microflora from actively progressing root surface caries lesions, in which mineral loss had been determined by quantitative microradiography. The caries lesions were produced experimentally in root surface specimens from human molars inserted in lower partial dentures carried for 3 months by six elderly individuals. A total of 780 bacterial isolates were identified from 13 plaque samples, collected with a punch technique, and six dentin samples. The composition of the microflora showed distinct individual differences. The microflora from plaque samples associated with the highest mineral loss was dominated by either Actinomyces viscosus or a combination of mutans streptococci (serotypes c, d, and f) and Lactobacillus species (L. casei and L. brevis). Plaque from root surfaces with less pronounced mineral loss harbored a more complex microflora comprising gram-positive rods, mutans streptococci, Streptococcus mitis biovar 1, Veillonella spp., gram-negative rods, and low numbers of lactobacilli. In the latter samples, individual variations in the proportions of mutans streptococci (serotypes c, d, and g), Actinomyces species (A. viscosus and A. naeslundii), and Veillonella parvula biotypes were observed. These findings suggest that certain species or combinations of species are more cariogenic than others and that dominance of single acidogenic species in particular is conducive to high caries activity.

A collection of 144 viridans group streptococcal strains recently characterized as part of a taxonomic study was examined for the ability to bind salivary alpha-amylase. This property was found in most strains of Streptococcus gordonii and Streptococcus mitis and in occasional strains of Streptococcus anginosus and Streptococcus salivarius. In contrast, all strains of Streptococcus sanguis, Streptococcus oralis, Streptococcus vestibularis, and Streptococcus mutans lacked alpha-amylase-binding capacity. A rapid and easy assay described in this paper may be an important supplementary test for identification of oral streptococci.