DNA restriction endonuclease cleavage pattern and protein antigen profile of Ehrlichia risticii

Molecular characterization of Ehrlichia risticii, the etiological agent of Potomac horse fever, was performed. Restriction endonuclease cleavage of E. risticii DNA generated distinct patterns by different enzymes. The DNA cleavage patterns of E. risticii isolates obtained from different geographic regions were similar. Protein analysis identified thirty-five distinct proteins with molecular weights ranging from 160 to 16 kilodalton (kDa). Antigenic analysis by radioimmunoprecipitation using 125I surface labeled E. risticii and by Western blotting determined the presence of eighteen antigens (160, 110, 86, 84, 81, 70, 55, 51, 49, 44, 41, 36, 33, 31, 28, 24, 22 and 16 kDa) of which nine (110, 86, 70, 55, 51, 49, 44, 33, and 28 kDa) were major antigens. Fourteen of these antigens, which included the major antigens, were apparent surface components. There were no heat-modifiable proteins but lipopolysaccharide components of 245 and 14 kDa, resistant to proteinase K and of non-antigenic character, were detected in the organism.