Motility in relation to virulence of Bacteroides nodosus

Fourteen Bacteroides nodosus isolates from footrot lesions of sheep were examined microscopically and all were found to have twitching motility. The mean percentage of cells showing motility was 40% and 9% for virulent and benign strains, respectively. This corresponded with mean agar colony diameters of 17 mm and 7 mm, respectively, for these strains. Two strains of intermediate virulence had values of motility and colony diameter similar to the benign strains. However, the intermediate and the virulent strains produced relatively stable protease compared to the benign strains. All virulent, benign and intermediate strains produced abundant pili. Included for comparison in this study was an avirulent variant strain which was highly motile, formed large colonies and produced stable protease, but showed no pili on electron microscopy. It was concluded that the properties of motility and protease stability may be used to distinguish, in the laboratory, wild-type virulent, benign and intermediate strains of B. nodosus.