Separation, Characterization, and Biological Significance of a Common Antigen in Enterobacteriaceae* by Calvin

An antigen common to members of the family Enterobacteriaceae detectable only by means of the hemagglutination test was recently described (1-3). I t was discovered during the course of a study using this test concerned with serologic interrelationships among the almost 145 known Escherickia coli 0 antigen groups (2). Good correspondence was obtained between O antigen groups and homologous rabbit antisera, and a limited number of cross-reactions among various O groups was also observed. In addition, erythrocytes coated with crude preparations of any of the E. coli 0 groups were agglutinated by rabbit antiserum to E. coli O14 and to a lesser extent by antiserum to O 56, 124, and 144. Subsequent studies revealed that the same reaction occurred with these antisera when erythrocytes were coated with crude lipopolysaccharides from other Enterobacteriaceae including Salmondla, Skigella, Proteus, and Aerobacter species, but not with similar preparations from numerous other Gram-negative or positive bacterial species. I t was postulated that the Enterobacteriaceae lipopolysaccharide possesses two types of antigenic determinants. One is the classic, specific O antigen; the other is common to all members of this family. E. coli O14 appears to differ from the others in its remarkable capacity to elicit antibody formation in rabbits to this common determinant. Antibody to the common antigen is present in significant amounts in human and other mammalian sera (2, 4), and must be removed, either by absorption or by preincubation with excess crude heterologous O antigen preparations, to permit measurement of specific antibody directed against the O antigen. If this is not done, as has been the case in almost all previously published studies, the hemagglutination test measures the sum of antibody to both the specific and the common antigen. The present report is concerned with the isolation of the common antigen by means of DEAE cellulose chromatography, with some of its physical, chem-