Antigenic relationships of the lipopolysaccharides of Escherichia hermannii strains with those of Escherichia coli O157:H7, Brucella melitensis, and Brucella abortus.

Clinical isolates of Escherichia hermannii which showed serological cross-reaction with polyclonal antisera to the O-polysaccharide portion of the lipopolysaccharide of E. coli O157 strains and with antisera to the O antigens of Brucella abortus and B. melitensis were found by chemical and nuclear magnetic resonance analyses to have lipopolysaccharide O chains composed of linear polymers containing 1,2- and 1,3-linked 4-acetamido-4,6-dideoxy-alpha-D-mannopyranosyl (alpha-D-Rhap4NAc) residues. Two O-antigen structures were identified; each had an unbranched pentasaccharide repeating unit, and one was composed of three 1,2- and two 1,3-linked alpha-D-Rhap4NAc residues and the other had two 1,2- and three 1,3-linked alpha-D-Rhap4NAc residues. The above-described cross-serological reactivities, which have led to false-positive identifications, are related to the common occurrence of epitopes involving the presence of N-acyl derivatives of 4-amino-4,6-dideoxy-D-mannopyranosyl residues in the O-polysaccharide portions of the respective lipopolysaccharides of the organisms. Strains of E. hermannii which did not show serological cross-reactions with E. coli O157 and Brucella antisera were found to have unique lipopolysaccharide O chains devoid of D-Rhap4NAc residues, demonstrating the existence of serotypes of E. hermannii that are distinct on the basis of their lipopolysaccharide components.