Study of humoral immunity to commensal oral bacteria in human infants demonstrates the presence of secretory immunoglobulin A antibodies reactive with Actinomyces naeslundii genospecies 1 and 2 ribotypes.

The mouths of three human infants were examined from birth to age 2 years to detect colonization of Actinomyces naeslundii genospecies 1 and 2. These bacteria did not colonize until after tooth eruption. The diversity of posteruption isolates was determined by ribotyping. Using immunoblotting and enzyme-linked immunosorbent assay, we determined the reactivity of secretory immunoglobulin A (SIgA) antibodies in saliva samples collected from each infant before and after colonization against cell wall proteins from their own A. naeslundii strains and carbohydrates from standard A. naeslundii genospecies 1 and 2 strains. A. naeslundii genospecies 1 and 2 carbohydrate-reactive SIgA antibodies were not detected in any saliva sample. However, SIgA antibodies reactive with cell wall proteins were present in saliva before these bacteria colonized the mouth. These antibodies could be almost completely removed by absorption with A. odontolyticus, a species known to colonize the human mouth shortly after birth. However, after colonization by A. naeslundii genospecies 1 and 2, specific antibodies were induced that could not be removed by absorption with A. odontolyticus. Cluster analysis of the patterns of reactivity of postcolonization salivary antibodies from each infant with antigens from their own strains showed that not only could these antibodies discriminate among strains but antibodies in saliva samples collected at different times showed different reactivity patterns. Overall, these data suggest that, although much of the salivary SIgA antibodies reactive with A. naeslundii genospecies 1 and 2 are directed against genus-specific or more broadly cross-reactive antigens, species, genospecies, and possibly strain-specific antibodies are induced in response to colonization.

The acid-tolerant microbiota associated with plaque from initial caries and healthy tooth surfaces.

The intent of this study was to compare the inherent acid tolerance of bacteria in samples of dental plaque from tooth sites in subjects with and without initial caries. Plaque was collected from approximal surfaces showing early enamel caries and from healthy tooth surfaces in the same subjects, as well as from enamel surfaces of caries-free individuals. In addition to plating on blood agar, the plaque samples were plated directly on non-selective solid agar medium buffered to pH 7.0, 6.0, 5.5, 5.0, 4.5 and 4.0 to avoid any loss of adaptation to acid during primary isolation of plaque bacteria. The results showed that approximately 50% of the total cultivable plaque microbiota from caries, as well as healthy tooth sites, was able to grow at pH 5.5 and 1% at pH 5.0, pH values regarded as critical for the demineralization of tooth enamel. At pH 5.0, members of the genus Streptococcus were the dominant group, but mutans streptococci accounted for less than half of the streptococcal viable count. The other acid-tolerant streptococcal isolates included Streptococcus anginosus, Streptococcus constellatus, Streptococcus gordinii, Streptococcus intermedius, Streptococcus mitis, Streptococcus oralis, Streptococcus salivarius and SStreptococcus sanguis. Analysis of the results indicated that the mutans streptococci in dental plaque were highly variable with respect to acid tolerance, and that both caries and healthy sites harboured significant numbers of mutans streptococci that were not acid-tolerant.

Identification of mouse submaxillary gland protein in mouse saliva and its binding to mouse oral bacteria.

The mouse submaxillary gland protein (mSMGP) is highly expressed in the submandibular gland of the adult mouse and rat. It shares 51% identity at the amino-acid level with a human protein, the prolactin-inducible protein (PIP)/gross cystic disease fluid protein 15 (GCDFP-15), which has been found in saliva, tears, sweat, seminal plasma, submucosal glands of the lung and amniotic fluid. More recently, the human PIP has been reported to bind to bacterial strains normally found in the mouth, ear canal and human skin. Sequence analysis of mSMGP/PIP earlier identified the presence of a signal peptide, suggesting that it is a secreted protein. Here, by Western blotting, mSMGP/PIP has been identified in mouse saliva. To investigate further the role of this secreted protein, its ability to bind specifically to oral bacteria was examined; the hypothesis was that mSMGP/PIP is involved in non-immune host defence by binding to bacteria. Several bacterial strains, found to belong to the genera Streptococcus, Aerococcus, Pseudomonas, Staphylococcus, Sphingomonas, Vibrio and Aeromonas, were isolated from the mouse oral cavity. Following incubation of these bacteria with (35)S-labeled, in vitro-translated mSMGP/PIP, the protein was found to bind specifically and selectively to several but not all strains tested, showing the highest affinity for the streptococci. The protein also bound specifically to an Aerococcus sp., and a low binding interaction with the Pseudomonas and Staphylococcus spp. was observed. The conservation of SMGP sequences among several animal species suggests that this protein may play an important part in the biology of the submandibular gland. As the function of the mSMGP/PIP is still undetermined, these findings provide insight into a possible involvement of this protein in host defence.