Comparative pathogenicity of Actinomyces species in mice.

The comparative pathogenicity of different species of Actinomyces was studied in a susceptible weanling-mouse model. After the intraperitoneal injection of strains of Actinomyces israeli, A. naeslundi, A. viscosus and Arachnia propionica, numerous abscesses developed in the intestine, mesentery, liver, and at the site of injection. Lesions were not produced by A. odontolyticus. A. naeslundi and A. viscosus produced acute lesions that resolved after a few weeks. Abscesses produced by rough strains of A. israeli and Arach. propionica persisted and led to a slowly progressive chronic infection. Viable organisms were always recovered from the lesions. Spread of the lesions by extension into other areas, including the thoracic cavity, led to the death of the animal after approximately 1 year. This study demonstrated a clear difference in the pattern of infection produced by the different species of Actinomyces as well as Arach. propionica.