Common antigenic determinant in a rumen organism and in salmonellae containing the antigen O4

Nineteen of 28 strains of rumen organisms isolated from a cow on a high roughage diet and identified morphologically as butyrivibrios, reacted to a low agglutinin titer with salmonella antisera, forming five groups. However only one strain reacted with polyvalent O salmonella antiserum. This strain reacted with O4 factor serum and with antisera to Salmonella strains containing the antigen O4, and agglutinin absorption tests showed the presence of an antigen identical to O4. When 16 further strains of butyrivibrio-like rumen organisms isolated from three cows and one steer were examined, one possessed an antigen similar to but not identical with the antigen O9, and two strains reacted with specific O6,7 factor serum but were not examined further. These four strains were presumptively identified by physiological tests as butyrivibrios. The possible site of antigenic stimulation by such organisms is discussed.