Soluble Antigens of Bacterium Enteritidis

Bacterium enteritidis can be cultivated in a synthetic medium free from protein. Berkef eld filtrates, free from bacteria, obtained after 6 to 14 days incubation, are extremely toxic for rabbits when given intravenously. These filtrates, when injected into rabbits, stimulate the production of agglutinins, precipitins, complement-fixing antibodies, and possibly antitoxins. The antigenic properties of these filtrates are increased when the liquids are concentrated by evaporation in vacuo. The products so obtained are better antigens than suspensions of Bact. enteritidis. Protein cannot be demonstrated even in the dry residue obtained by the evaporation of such a filtrate. An opalescent fluid and a gray precipitate are obtained when this dry residue is dialyzed. Protein cannot be demonstrated in either of these fractions. The precipitate contains carbohydrate. Further concentration of the opalescent fluid gives a liquid that gives very faintly positive reactions for tryptophane and histidine, and a faintly positive ninhydrin reaction. Protein was, therefore, possibly present. An amount of filtrate that could, at most, have contained 0.000,003 to 0.000,004 gm. of protein led to definite antibody formation. Whether or not so small an amount of protein can, in fact, be held exclusively responsible for this antibody production may be questioned. Such a possibility should, however, be borne in mind in interpreting results obtained with apparently protein-free materials.