Two-way cross-reactions between serotypes of Actinomyces viscosus.

Three antigen preparations were obtained from cultures of A. viscosus Serotypes 1 and 2. Ammonium sulphate (60 per cent w/v) and acetone precipitates were obtained from cellfree culture supernatants of late-log phase cultures of each organism. The third preparation consisted of the supernatant obtained after homogenization of late-log phase cells of each organism. Immunodiffusion and immunoelectrophoresis using rabbit antisera to each serotype were used to identify the soluble antigens present in each preparation. Ammonium sulphate preparations proved to be the most reproducible and contained the greatest number of identifiable antigens. Homologous and cross-reacting antigens were identified and two-way cross-reactions were observed between the serotypes.