A reexamination of the O1 lipopolysaccharide antigen group of Escherichia coli.

A total of 64 Escherichia coli strains of the O1 serogroup were tested for the migration pattern of their lipopolysaccharides (LPS) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. O1:K1 and O1:K51 strains of the OMP5 outer membrane protein pattern possessed LPS with a doublet pattern (O1A1) or the lowermost band of the O1A1 doublet (O1A2). O1:K1 strains of the OMP9 pattern possessed LPS referred to as O1A, which corresponded to the uppermost band of the O1A1 doublet pattern. A few O1:K? strains possessed LPS of different migration patterns (O1B and O1C). O1A and O1A1 LPS were indistinguishable by chemical techniques, and both reacted with each of 10 different monoclonal antibodies tested. However, O1A1 had an additional epitope within the additional band in each doublet, as demonstrated by adsorption experiments with hyperimmune rabbit sera followed by Western blotting. Furthermore, purified polysaccharide from O1A bacteria was incapable of inhibition in enzyme-linked immunosorbent assays performed with O1A1 LPS as antigen and adsorbed, specific anti-O1A1 antibodies, whereas O1A1 polysaccharide inhibited this reaction. O1B and O1C LPS differed in all respects tested, including chemical composition, from O1A and O1A1 LPS.