Abscess induction in mice. Abscess formation was induced when 0.5 ml of bacterial cell suspension (2 × 107 CFU/ml) of Prevotella intermedia strains 17 and OD1-16 was injected into the inguinal area of a mouse. In contrast, subcutaneously injected P. intermedia ATCC 25611, Porphyromonas gingivalis ATCC 33277, 381 and W83 (0.5 ml at a concentration of 2 × 108 CFU/ml) failed to induce an abscess in the mice. When these strains were injected at a higher concentration (2 × 109 CFU/ml), abscess formation was ultimately induced. The data are representative from one of two independent experiments.