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.