Abstract: The specificity of monoclonal antibodies for E. coli LPS-core type was comfirmed ,but monoclonal antibodies specific for R₄ or K₁₂ core types were not available. Polyclonal antiseria (Pabs) which made by immunization with rought mutants of E. coli to the rabbits were made monospecific for a given E. coli LPS-core type by absorbtion. We decided that a tentative core type would be assigned to a bacterial strain if the ODobtained with one of the five absorbed Pabs (anti-R₁-R₄ and anti-K₁₂) was at least twice that of the others. According to the standard, Pabs and monoclonal antibodies yielded identical outcomes concering the core type assigned (only R₁, R₂ and R₃ core types). We discovered a novel core type, expressing both the R₁ and R₄ immunospecificity in the E. coli strains isolated from bacteremic patients (13strains/138 strains). They were resistant to proteolytic digestion and sensitive to periodate.After blocking the lipid Aand inner core (kdo-heptose) of the E. coli strains by r-BPI and clone 20 respectively. The reactivity of the both anti-R₁ and anti-R₄ Pabs with the E. coli strains was the same as before, it was indicated that the antigens which were recongnized and combined by anti-R1 and anti-R4 Pabs were neither proteins/peptide nor lipid Aand inner core(kdo-heptose). It should be outer core hexose antigens. We therefore assigned the R₁R₄ mixed core type to these strains, a core type not yet described in the literature.

Key words: E. coli, core type, polyclonal antiserum