Phospholipid substitution of capsular (K) polysaccharide antigens fromEscherichia colicausing extraintestinal infections

The capsular antigens of Escherichia coli causing extraintestinal infections have been analyzed extensively. The K1 antigen which is identical with the capsular antigen of Neisseria meningitidis B [1] has been described by McGuire and Binkley [2] and by Orskov et al. [3]. We have recently reported the structures of the K2, K5, K12, K62 and K82 antigens ([4-7]; Schmidt, M.A. and Jann, K., in preparation). During our study we have found that these K antigens, which are all acidic polysaccharides, tend to aggregate in aqueous solutions. The aggregation could be abolished with Triton X-100, by very mild acid hydrolysis and by treatment with alkali. These results indicated that the polysaccharides contain a lipid moiety in a labile linkage. We report here the characterization of the capsular polysaccharide antigens and the analysis of the lipid moiety of the K I2 and K82 antigens. The lipid was shown to be a phosphatidic acid. During the preparation of this manuscript similar studies were reported by Gotschlich et al. [8] concerning the polyneuraminic acid antigens of Neisseria and also the K92 antigens E. coli. Our results are in agreement with those of Gotschlich et al. and show that termination of these E. coli K antigens with a phospholipid seems to be a general structural feature. 2.1. Bacteria and cultivation