Dot blot hybridization shows the specificities of the three probes hybridized with different Streptococcus reference strains as well as with S. sanguinis clinical isolates. Probe SSA-2 was specific for type strain ATCC 10556 (B) and all S. sanguinis clinical isolates (D). SSA-1 and SSA-3 showed different degrees of hybridization to other species (A and C). The bacterial strains tested were as follows: 1, S. sanguinis; 2, S. oralis; 3, S. gordonii; 4, S. cristatus; 5, S. oralis; 6, S. mitis; 7, S. parasanguinis; 8, S. pneumoniae; 9, S. mutans; 10, S. salivarius; 11, S. sobrinus; 12, S. ratti; 13, S. vestibularis; 14, A. naeslundii; 15, L. acidophilus; 16, E. coli JM109.