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Specific immune defense against cariogenic mutans streptococci is provided largely by salivary secretory IgA antibodies, which are generated by the common mucosal immune system. This system is functional in newborn infants, who develop salivary IgA antibodies as they become colonized by oral microorganisms. The mechanisms of action of salivary IgA antibodies include interference with sucrose-independent and sucrose- dependent attachment of mutans streptococci to tooth surfaces, as well as possible inhibition of metabolic activities. The goal of protecting infants against colonization by mutans streptococci might be accomplished by applying new strategies of mucosal immunization that would induce salivary IgA antibodies without the complications of parenteral immunization. Strategies of mucosal immunization against mutans streptococci currently under development include the use of surface adhesins and glucosyltransferase as key antigens, which are being incorporated into novel mucosal vaccine delivery systems and adjuvants. The oral application of preformed, genetically engineered antibodies to mutans streptococcal antigens also offers new prospects for passive immunization against dental caries.

Previous immunofluorescence (IF) studies have indicated that Streptococcus mutans may preferentially colonise specific sub-sites within approximal plaque. The present study aimed to extend these observations to other mutans streptococci and lactobacilli in such gingival margin plaque. Two hundred and seventy approximal plaque samples were taken from 90 teeth (3 from each tooth) in 64 children; three gingival margin sub-sites in relation to the contact area: away from (A), to the side of(S) and below (B) the contact area. Samples were processed by indirect IF using high-titred polyclonal anti-S. mutans 'c', anti-S. sobrinus 'd', anti-L. casei and anti-L. acidophilus antisera. An overall positive association was found between S. mutans 'c' and S. sobrinus 'd' (p < 0.001). Significant differences (p < 0.1) were found between the proportional counts at each sub-site for S. mutans 'c': A = 39%, S = 51% and B = 70%, and for S. sobrinus 'd' 21, 33 and 49%. Mutans streptococci (MS) appeared to preferentially colonise the sub-site below the contact area (B = 81%), compared with sub-sites A and S (48 and 62%, respectively). S. mutans 'c' and S. sobrinus 'd' were detected together at subsites A = 12%, S = 22%, and B = 38%, with proportional counts at B sites being higher than those at A (B > A, p < 0.01, and B > S, p < 0.05). Lactobacillus spp. were isolated rarely, and were usually found together with MS. There was a positive relationship between the presence of lactobacilli or MS and caries (white spot lesions only), although these species could frequently be isolated from noncarious sites. The presence of both S. mutans 'c' and S. sobrinus 'd' were strongly correlated with early caries lesions. In addition, this study confirmed the variation in the microflora at different sub-sites within approximal dental plaque.

Passive immunization has been suggested as a method to prevent colonization of teeth by mutans streptococci. However, the mechanism of action of antibodies, both polyclonal and monoclonal, is not clear. In this study we investigated the effect of polyclonal antibodies (pAbs) and a monoclonal antibody (OMVU10) on the chain length and growth of Streptococcus sobrinus. During growth in broth S. sobrinus formed significantly longer chains in the presence of pAbs in comparison to pre-immune serum (p < 0.01), but pAbs did not influence the growth rate of S. sobrinus in broth. OMVU10 did not influence the growth rate nor the chain length. In order to study the effect of the antibodies on adhesion and growth on a surface, S. sobrinus was grown on hydroxyapatite discs in the presence of two other bacteria, Streptococcus oralis and Actinomyces viscosus. No effect of the antibodies was found on the total cultivable count of the three bacteria after growth on hydroxyapatite discs. However, the morphology of the S. sobrinus microcolonies was different after growth in the presence of both pAbs and OMVU10. The colonies were less dense and chains of S. sobrinus could be seen using a confocal laser microscope. After growth in the presence of the control antibodies, the colonies were dense and no long chains could be observed. It was concluded that pAbs influenced the chain length, in broth and on hydroxyapatite discs, and the colony morphology of S. sobrinus on hydroxyapatite discs, whereas OMVU10 influenced the colony morphology of S. sobrinus on hydroxyapatite discs.

Local passive immunization has been suggested as a method of preventing colonization of teeth by mutans streptococci. In this study we describe the effect of local application of monoclonal antibodies (Mabs) on the colonization of Streptococcus sobrinus. The rats, 37 days old, were divided in 4 groups: group 1 received Mab OMVU10 (Mab reactive with Antigen B of S. sobrinus, IgG2b), group 2 received Clone 24 (Mab reactive with lipid A of Escherichia coli, IgG2b), group 3 received uninoculated culture medium, and group 4 received phosphate-buffered saline (PBS). Mabs were applied 6 times on the surfaces of the molars and the labial surfaces of the incisors of the rats, on days 37, 40, 44, 46, 49 and 54 after birth. After the third application of Mabs, all rats were inoculated with S. sobrinus (day 45). Subsequently, the rats were fed a cariogenic diet containing 20% sucrose and 5% glucose. The rats were killed 34 days after inoculation and the maxillary molars were extracted and homogenized in order to determine the numbers of S. sobrinus. The proportions of S. sobrinus, expressed as a percentage of the total cultivable microflora, in rats which received OMVU10 (group 1) were 23.1 +/- 14.8%, whereas in rats which received Clone 24, culture medium or PBS the levels were 34.5 +/- 11.3%, 40.7 +/- 14.9% and 36.7 +/- 9.7%, respectively. Statistical analysis showed that the level of colonization of rats which received OMVU10 was significantly lower than that of rats which received Clone 24, culture medium or PBS (p < 0.001, p < 0.013 and p < 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

We have studied the possible relationship between indigenous salivary antimicrobial agents, indigenous mutans streptococci and the capability of added mutans streptococci to grow in saliva. Stimulated whole saliva was collected from 19 healthy donors. Saliva samples were sterilized, supplemented with glucose and inoculated with Streptococcus mutans or Streptococcus sobrinus. The mixtures were incubated for 20 h followed by counting of viable cells. Saliva samples were analysed, both before and after sterilization, for indigenous antimicrobial agents and the bacterial flora. The subjects could be divided into two groups: those (n = 9) whose saliva promoted and those (n = 10) whose saliva inhibited the growth of the inoculated streptococci. A statistically significant correlation (+0.82, p < 0.001) was found between the numbers of viable cells of S. mutans and S. sobrinus after incubation in saliva. The sterilization procedure reduced the content of all antimicrobial proteins. Salivary antimicrobial factors, or levels of indigenous mutans streptococci, did not differ between the two groups. We conclude that none of the individual salivary antimicrobial factors alone can explain the large individual differences in growth-promoting or growth-inhibiting patterns of saliva on S. mutans and S. sobrinus. Inter-individually, saliva either supports or inhibits the growth of mutans streptococci, indicating a similar response of these two species in relation to the properties of saliva.