Streptococcus mutans major adhesion surface protein, P1 (I/II), does not contribute to attachment to valvular vegetations or to the development of endocarditis in a rat model.

Streptococcus mutans P1 antigen functions as an adhesion factor for binding to salivary pellicle on tooth surfaces. It induces increased antibody titres in patients with Strep. mutans endocarditis. A mutant of Strep. mutans deficient in the function of the gene (spa P) encoding the surface antigen P1, and its isogenic parental strain, were used in a rat endocarditis experiment. Absence of P1 did not decrease adhesion to vegetations determined l h after intravenous infection. The number of bacteria recovered from valvular vegetations after 48 h from animals with manifest endocarditis did not differ between the strains. Consequently, the Pl antigen appears to be unimportant both for adhesion and virulence in endocarditis caused by Strep. mutans.