Structural and Serological Studies of the O-Antigen of the Bacterium Proteus mirabilis OXK (Serogroup O3) Used in the Weil--Felix Test

A. S. Swierzko,¹ M. Cedzynski,¹ Yu. A. Knirel,^2,3 S. N. Senchenkova,² N. A. Kocharova,² A. S. Shashkov,² K.-I. Amano,⁴ K. Kyohno,⁴ and W. Kaca¹

¹Center of Microbiology and Virology, Polish Academy of Sciences, ul. Lodowa 106, 93-232 Lodz, Poland; fax: (48-42) 49-16-33.

²Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii pr. 47, Moscow V-334, GSP-1, 117913 Russia; fax: (7-095) 135-53-28; E-mail: knirel@ioc.ac.ru

³To whom correspondence should be addressed.

⁴Central Research Laboratory, School of Medicine, Akita University, Akita 010, 1-1-1 Hondo, Japan.

Submitted September 20, 1996.

Sugar analysis and ¹H- and ¹³C-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 chain having the following structure: (see full article for figure), where GlcA and GalA are glucuronic and galacturonic acids, respectively. This polysaccharide which defines the O3 specificity of Proteus and has been found earlier in an unclassified P. mirabilis strain S1959, contains an amide of D-galacturonic acid with L-lysine which plays an important role in manifesting the immunospecificity. A cross-reaction was observed in ELISA between sera from patients with scrub typhus, caused by the bacterium Orientia (Rickettsia) tsutsugamushi, and purified LPS of P. mirabilis OXK, 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 strain Gilliam in dot-blotting and Western blotting, and the nature of the rickettsial antigen responsible for the Weil--Felix reaction remains unknown.

KEY WORDS: lipopolysaccharide, O-specific polysaccharide, structure, serological cross-reactivity, scrub typhus, Weil--Felix test, Proteus mirabilis, Orientia tsutsugamushi.

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