Monoclonal antibodies against the capsular K antigen of Escherichia coli (O9:K30(A):H12): characterisation and use in analysis of K antigen organisation on the cell surface.

Monoclonal antibodies were produced against the capsular antigen of Escherichia coli serotype K(A)30, using a mouse hybridoma system. The antibodies also recognised the chemically identical capsular polysaccharide produced by Klebsiella K20. Chemical modification of the K30 polysaccharide indicated that the glucuronic acid residues found in the E. coli K30 capsular antigen were important in the epitope recognised by these antibodies. Use of the antibodies as molecular probes revealed the presence of two discrete forms of the K30 antigen. One form was comprised of high molecular weight polysaccharide, present as a surface capsular layer. The second form of the antigen was of low molecular weight and was associated with lipopolysaccharide fractions from cell surface polysaccharide extracts. Separation of lipopolysaccharide fractions using gel chromatography in the presence of detergent showed that the low molecular weight K-antigenic fraction comigrated with a lipopolysaccharide lipid A core fraction present in encapsulated E. coli K30 bacteria but absent in acapsular mutants.

Transfer and expression of the genetic determinants for O and K antigen synthesis in Escherichia coli O9:K(A)30 and Klebsiella sp. O1:K20, in Escherichia coli K12.

Escherichia coli serotype O9:K(A)30 and Klebsiella O1:K20 produce thermostable capsular polysaccharides or K antigens, which are chemically and serologically indistinguishable. Plasmid pULB113 (RP4::mini-Mu) has been used to mediate chromosomal transfer from E. coli O9:K30 and Klebsiella O1:K20 to a multiply marked, unencapsulated, E. coli K12 recipient. Analysis of the cell surface antigens of the transconjugants confirmed previous reports that the genetic determinants for the E. coli K(A) antigens are located near the his and rfb (O antigen) loci on the E. coli linkage map. The Klebsiella K20 capsule genes were also found to be in close proximity to the his and rfb loci. Electron microscopy revealed significant differences in the structural organization of capsular polysaccharides in these two microorganisms and the morphological differences were also readily apparent in transconjugants expressing the respective K antigens. These results are consistent with the interpretation that at least some of the organizational properties of capsular polysaccharides may be genetically determined, rather than being a function of the outer membrane to which the capsular polysaccharides are ultimately attached.