STRUCTURAL AND SEROLOGICAL STUDIES OF THE O-ANTIGEN OF THE BACTERIUM PROTEUS-MIRABILIS OXK (SEROGROUP O3) USED IN THE WEIL-FELIX TEST

Sugar analysis and H-1- and C-13-NMR spectroscopic studies showed that various strains of Proteus mirabilis OXK used as antigens in the Weil -Felix test for serodiagnosis of rickettsiosis (scrub typhus) produce lipopolysaccharides (LPSs) with the same O-specific polysaccharide cha in having the following structure: [GRAPHICS] where GlcA and GalA are glucuronic and galacturonic acids, respectively. This polysaccharide w hich defines the O3 specificity of Proteus and has been found earlier in an unclassified P. mirabilis strain S 1959, contains an amide of D- galacturonic acid with L-lysine which plays an important role in manif esting the immunospecificity. A cross-reaction was observed in ELISA b etween sera from patients with scrub typhus, caused by the bacterium O rientia (Rickettsia) tsutsugamushi, and purified LPS of P. mirabilis O XK, thus suggesting that the common epitope involved in the Weil-Felix test is located on P. mirabilis OXK LPS. Rabbit anti-P. mirabilis OXK antibodies did not cross-react with LPS-lacking O. tsutsugamushi stra in Gilliam in dot-blotting and Western blotting, and the nature of the rickettsial antigen responsible for the Weil-Felix reaction remains u nknown.