Characterization of Streptococcus gordonii (S. sanguis) PK488 adhesin-mediated coaggregation with Actinomyces naeslundii PK606

Characterization of Veillonella atypica PK1910 adhesin-mediated coaggregation with oral Streptococcus spp

The gram-negative human oral bacterium Veillonella atypica PK1910 exhibits both lactose-inhibitable and lactose-noninhibitable coaggregations with certain human oral streptococci. A mild sonication procedure was used to obtain a veillonella surface protein preparation against which antisera were prepared. To characterize the lactose-inhibitable coaggregation, coaggregation-defective (COG-) mutants unable to exhibit this kind of coaggregation (class 1 mutants) were used to absorb the antisera. Only the lactose-inhibitable coaggregations were blocked by these absorbed antisera. The absorbed antiserum also reacted with a 45-kDa protein found in the parent and in class 2 COG- mutants that exhibited lactose-inhibitable coaggregation. This protein was not detected in surface protein preparations of class 1 COG- mutants. Two affinity protocols, involving agarose-lactose beads and the streptococcal coaggregation partner cells, were used to bind surface proteins from V. atypica PK1910. In each protocol, the 45-kDa protein was eluted by a solution containing 100 mM lactose. Antiserum was prepared against agarose-lactose beads with bound 45-kDa protein. When absorbed with class 1 COG- mutants, the antiserum blocked lactose-inhibitable coaggregation and reacted with the 45-kDa protein in immunoblots. When the same antiserum was absorbed with class 2 COG- mutant cells, it lost both properties, suggesting that the 45-kDa protein is an adhesin that mediates coaggregation with streptococci. The proposed adhesin does not seem to be the structural subunit of veillonella fimbriae, since no differences in fimbriae were observed by electron microscopy of the parent and all three classes of mutants.

Nucleotide sequence of a gene coding for a saliva-binding protein (SsaB) from Streptococcus sanguis 12 and possible role of the protein in coaggregation with actinomyces

The nucleotide sequence of a 2.9-kb streptococcal DNA fragment which codes for two proteins with MrS of 36,000 (Streptococcus sanguis adhesin B [SsaB]) and 20,000 has been determined. The ssaB gene is 927 bp and codes for a 34,684-Da protein. The open reading frame coding for the 20-kDa protein is 489 bp and codes for a protein of 17,885 Da. The SsaB protein has a putative hydrophobic 19-amino-acid signal sequence resulting in a 32,620-Mr secreted protein, whereas the 20-kDa protein has no signal sequence. Both proteins are hydrophilic, and neither appears to have a hydrophobic membrane anchor sequence in the carboxy-terminal region. A DNA sequence homology of 73% exists between the cloned fragment containing the ssaB gene from S. sanguis 12 and the cloned fragment containing the type 1 fimbrial gene of S. sanguis FW213 (J.C. Fenno, D.J. LeBlanc, and P. Fives-Taylor, Infect. Immun. 57:3527-3533, 1989). Amino acid comparisons of the SsaB and type 1 fimbrial proteins show 87% homology, indicating a close similarity of the two proteins. Antiserum raised against the cloned SsaB protein cross-reacts with a 38-kDa protein identified from Streptococcus gordonii (S. sanguis) PK488 which was proposed to mediate coaggregation with Actinomyces naeslundii PK606 (P.E. Kolenbrander and R.N. Andersen, Infect. Immun. 58:3064-3072, 1990). The SsaB adhesion may play a role in oral colonization by binding either to a receptor on saliva or to a receptor on actinomyces.

Intrageneric coaggregation among strains of human oral bacteria: potential role in primary colonization of the tooth surface

Of the 122 human oral bacterial strains tested from 11 genera, only streptococci and a few actinomyces exhibited coaggregation among the strains within their respective genera. Eight of the ten streptococci showed multiple intrageneric coaggregations, all of which were inhibited by galactosides. The widespread intrageneric coaggregation among the streptococci and the less extensive coaggregation among the actinomyces offers an explanation for their accretion on cleaned tooth surfaces and their dominance as primary colonizers.