Streptobacillus actinoides (Bacillus actinoides): isolation from pneumonic lungs of calves and pathogenicity studies in gnotobiotic calves.

Pneumonic lungs of 56 calves were examined and 12 (21 per cent) of them yielded Streptobacillus moniliformis-like organisms. These organisms resembled those previously described as Bacillus actinoides or Actinobacillus actinoides. After intratracheal inoculation of cultures of two strains of these organisms, pneumonic consolidation developed in five out of six gnotobiotic calves and involved up to 16 per cent of the lung surface. Histological lesions of interstitial pneumonia were observed in the lungs of all six calves. Swellings at the site of the infection followed intradermal and subcutaneous inoculation of cultures of all strains in calves. Mice showed no signs of illness following intraperitoneal injection of three stains. The bacteriological findings suggested that a more appropriate name for these organisms would be Streptobacillus actinoides.