Chemical properties of lipopolysaccharides from spotted fever group rickettsiae and their common antigenicity with lipopolysaccharides from Proteus species.

The lipopolysaccharides (LPS) isolated from spotted fever group (SFG) rickettsia strains Thai tick typhus TT-118 and Katayama were characterized by chemical analyses, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, enzyme-linked immunosorbent assay (ELISA), and immunoblotting. These LPS did not contain heptose, but they contained 3-deoxy-D-manno-octulosonic acid (KDO), glucosamine, quinovosamine, phosphate, ribose, an unknown neutral sugar, and palmitic acid. Resolution of the apparent molecular masses of these LPS by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and staining with silver showed ladder-like bands. In an ELISA, convalescent-phase sera from 10 patients with Japanese spotted fever reacted with LPS from the Katayama strain, and 90% (9 of 10) of these sera also reacted with LPS isolated from Proteus vulgaris OX2. Immunoblotting revealed that the sera reacted with the high-molecular-mass bands of LPS from SFG rickettsiae, in addition to those of OX2 LPS. In an ELISA, immunoglobulin M antibodies from these sera reacted with the O-polysaccharide and lipid A portions of LPS from P. vulgaris OX2. The epitopes common to LPS of SFG rickettsiae and P. vulgaris OX2 may be in the O-polysaccharide and lipid A portions.