Urinary purine derivative (PD) excretion was estimated to examine the effect of rumen protozoa on total PD excretion in goats fed hay and a concentrate diet. The effect of increasing protozoa number in the rumen on nitrogen (N) balance and urinary PD excretion was determined after inoculation. Protozoa increased slowly until 4 days after inoculation, and on the 5th day after inoculation rapidly, finally (10 days) reaching 4·1×105/ml of rumen contents similar to that before defaunation. Urinary N excretion showed a small (non-significant) decrease. Urinary PD excretion did not change until the 7th day, and then the level decreased on the 8th day after faunation presumably due to the effect of increased protozoa in the rumen. The mean urinary total PD excretion significantly (P<0·05) decreased in the defaunated group compared with that in the faunated group. Comparable changes were not seen in plasma PD level of faunated and defaunated groups.

The interaction of salivary lysozyme with the surface protein antigen (PAc) of Streptococcus mutans and the interaction of lysozyme with the pathogen were examined by ELISA using S. mutans MT8148 (PAc+) and the PAc-defective mutant EM-2 (PAc-). The lysozyme clearly bound to the S. mutans wild type but not to the S. mutans mutant. Furthermore, lysozyme bound directly in the fluid phase to the rPAc, of which the binding kinetics were determined (Kon = 3.63 +/- 0.04 x 10(3) M-1 s-1, K(off) = 1.72 +/- 0.04 x 10-5 s-1 and Kon/K(off) = 2.11 x 10(8) M-1) using surface plasmon resonance. The kinetics of both association and dissociation were relatively slow. In addition, anti-lysozyme antibody significantly inhibited the binding of salivary components to the rPAc. The present findings indicate that lysozyme is one of the major salivary components interacting with S. mutans PAc.