Cross-reactivity between six Enterobacteriaceae complete lipopolysaccharide core chemotypes

To gain insight into the value of lipopolysaccharide (LPS) core determinant s for cross-protective immunisation the serological relationships between s ix complete (LPS) core types from Enterobacteriaceae were investigated. Hyp erimmune sera were raised in mice by repeated immunisation with heat-killed strains of Salmonella choleraesuis (Ra core type) or Escherichia coli (cor e types R1, R2, R3, R4 and K12) and characterised for reactivity with compl ete and incomplete core chemotypes by ELISA and immunoblotting, Three sera (anti-Ra, anti-R2 and anti-R3) reacted strongly with 3-5 different complete core types whereas the other three (anti-R1, anti-R4 and anti-K12) reacted strongly only with their homologous core types in these assays. Two approa ches were used to examine further the structural bases for cross-reactivity between these cores. By the first approach the anti-complete-core sera wer e tested for cross-reactivity with truncated forms of the Salmonella specie s core (incomplete cores) derived from core-defective mutants. By the secon d approach, antisera raised against some core-defective mutants were tested for cross-reactivity with complete cores. The results of these investigati ons revealed that several pair-wise combinations of core types can be used as immunogens to elicit immune responses that recognise all six core types and that the major determinants which mediate cross-reactivity between comp lete cores are localised in the outer core region.