Production of common antigen by enteric bacteria grown in a synthetic culture medium

Enterobacteriaceae share a common antigen (CA). The present investigation was carried out to determine whether this antigen is produced by representative strains of Escherichia, Salmonella, and Serratia grown in a completely synthetic medium. For comparative purposes, antigen production by the same strains grown in infusion broth was determined. CA, as assayed by indirect hemagglutination and immunogenicity studies in the rabbit, was produced by the microorganisms cultured in both media. The amount of CA produced by the strains varied according to the size of microbial population and to the length of culture. With the exception of E. coli O14, the strains studied, on day 7, produced 1.4 to 8 times more CA in infusion broth than in the synthetic medium; with E. coli O14, the ratio of CA in the respective media was 96:1. E. coli O14, but not E. coli O111 or S. typhimurium, when grown in the synthetic medium, engendered CA antibodies upon intravenous injection into rabbits. Ethanol extraction of the latter two strains yielded an immunogenic ethanol-soluble antigen preparation. The ethanol-soluble fraction of E. coli O111 also induced a secondary response in animals primed with E. coli O111 or S. typhimurium cultures grown in the synthetic medium. It is concluded that CA produced in a completely synthetic culture medium has the same attributes as CA produced in infusion broth.