Experimental actinomycosis caused by Actinomyces-like bacteria in mice and a sow.

The present experiment was performed to test the pathogenicity of Actinomyces-like bacteria in experimental animals and swine. Two rough (R) strains of Actinomyces-like bacteria isolated from a site of arthritis and from the tonsil in pigs were used as inocula. To investigate their susceptibility to Actinomyces-like bacteria, BALB/c, SS and ddY mice and guinea-pigs were inoculated intraperitoneally with the strains of Actinomyces-like bacteria. The ddY mice were used for the long-term observation of Actinomyces-like bacteria lesions and the mammary tissue of a sow was inoculated with Actinomyces-like bacteria isolated from swine tonsil. Macroscopic observation revealed many abscesses on the surfaces of the abdominal and/or thoracic organs in the mice, but not on those of the guinea-pigs. The sow developed firm nodules at the inoculation site in the mammary glands. Histopathologically, the lesions in the mice were characterized as actinomycotic abscesses in the early stage and as pus-forming granuloma (PFG) in the advanced stage; the lesions were accompanied by crystalloid particles. Actinomyces-like bacteria induced granulomatous mastitis in the sow, and the lesion was characterized as PFG. The characteristic actinomycotic lesions in swine mammary glands were reproduced by experimental infection.