Lactobacilli have previously been used to deliver vaccine components for active immunization in vivo. Vectors encoding a single-chain Fv (scFv) antibody fragment, which recognizes the streptococcal antigen I/II (SAI/II) adhesion molecule of Streptococcus mutans, were constructed and expressed in Lactobacillus zeae (American Type Culture Collection (ATCC) 393). The scFv antibody fragments secreted into the supernatant or expressed on the surface of the bacteria showed binding activity against SAI/II in enzyme-linked immunosorbent assay (ELISA), and surface scFv-expressing lactobacilli agglutinated SAI/II-expressing S. mutans in vitro without affecting the corresponding SAI/II knockout strain. Lactobacilli expressing the scFv fragment fused to an E-tag were visualized by scanning electron microscopy (SEM) using beads coated with a monoclonal anti-E-tag antibody, and they bound directly to beads coated with SAI/II. After administration of scFv-expressing bacteria to a rat model of dental caries development, S. mutans bacteria counts and caries scores were markedly reduced. As lactobacilli are generally regarded as safe (GRAS) microorganisms, this approach may be of considerable commercial interest for in vivo immunotherapy.

The role of Streptococcus mutans in the development of dental caries is well recognized. Important virulence factors include the glucosyltransferases (gtf), essential for production of glucans. We evaluated the anticariogenic effects of orally administered chicken anti-cell-associated (CA) Gtf antibodies in desalivated rats. The animals were infected with S. mutans MT8148R and treated with chicken anti-CA-Gtf egg yolk antibodies (IgY) or nonimmune egg yolk powder. Smooth surface lesions were significantly lower in the anti-CA-Gtf-treated group in comparison to the control groups. Sulcal surface caries was also decreased and of less severity. Our study suggests that chicken anti-CA-Gtf antibodies may have promise as a prophylaxis for high caries risk patients.

We compared the anticariogenic effect of lactobacilli expressing a single-chain antibody (scFv) against the SA I/II adhesin of Streptococcus mutans under the control of an inducible or a constitutive promoter. Both lactobacilli expressed equal amounts of scFv and agglutinated S. mutans bacteria expressing SA I/II to a similar level. In a rat caries model, transformed lactobacilli could be detected in the oral cavity throughout the duration of the study. Transformants containing the constitutive promoter were slightly more protective than those containing the inducible promoter suggesting that continuous in situ production of scFv in the oral cavity may be therapeutically superior to intermittent production.

Streptococcus mutans is the main cause of dental caries. We evaluated the therapeutic effect of variable regions of a llama heavy chain antibody fragments directed against S. mutans named S36-VHH (S for Streptococcus) alone or fused with glucose oxidase (GOx) from Aspergillus niger. Western blot analysis and ELISA revealed binding of the S36-VHH to the streptococcal antigen I/II adhesin molecule of S. mutans serotype C. In a rat-desalivated caries model, daily administration of S36-VHH significantly reduced the development of smooth surface caries. No additional therapeutic effect of GOx was observed. Our results suggest that llama VHH antibodies may be a potential benefit as prophylaxis against dental caries.

Salivary proline-rich proteins (PRPs) attach commensal Actinomyces and Streptococcus species to teeth. Here, gel filtration, mass spectrometry and Edman degradation were applied to show the release of a pentapeptide, RGRPQ, from PRP-1 upon proteolysis by Streptococcus gordonii. Moreover, synthetic RGRPQ and derivatives were used to investigate associated innate properties and responsible motifs. The RGRPQ peptide increased 2.5-fold the growth rate of S. gordonii via a Q-dependent sequence motif and selectively stimulated oral colonization of this organism in a rat model in vivo. In contrast, the growth of Streptococcus mutans, implicated in caries, was not affected. While the entire RGRPQ sequence was required to block sucrose-induced pHdecrease by S. gordonii and S. mutans, the N-terminal Arg residue mediated the pH increase (i.e., ammonia production) by S. gordonii alone (which exhibits Arg catabolism to ammonia). Strains of commensal viridans streptococci exhibited PRP degradation and Arg catabolism, whereas cariogenic species did not. The RGRPQ peptide mediated via a differential Q-dependent sequence motif, adhesion inhibition, and desorption of PRP-1-binding strains of A. naeslundii genospecies 2 (5 of 10 strains) but not of S. gordonii (n ‫؍‬ 5). The inhibitable A. naeslundii strains alone displayed the same binding profile as S. gordonii to hybrid peptides terminating in RGRPQ or GQSPQ, derived from the middle or C-terminal segments of PRP-1. The present findings indicate the presence of a host-bacterium interaction in which a host peptide released by bacterial proteolysis affects key properties in biofilm formation.

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