A comparative view of Rickettsia tsutsugamushi and the other groups of rickettsiae

Recent researches on the rickettsial group microorganisms are summarized in their comparative aspects of morphology, cultivation and multiplication, susceptibility to chemotherapeutics, chemical structure of envelopes, nucleic acid, protein constitution, and gene structures. From this overview, Rickettsia tsutsugamushi seems to have different properties from the others and should be reclassified into a new genus, and a new species name as Orientia tsutsugamushi is proposed.

Purification and partial characterization of a type-specific antigen of Rickettsia tsutsugamushi

A type-specific antigen (54- to 56-kilodalton polypeptide) in the envelope of Rickettsia tsutsugamushi was purified from each of three prototype strains (Gilliam, Karp, and Kato) by a combination of mild anionic detergent treatment, gel filtration, and reverse-phase high-performance liquid chromatography. The purified antigens from the three strains were shown to have similar amino acid compositions: primarily aspartic acid, glutamic acid, and glycine, with lesser amounts of cysteine, methionine, and tyrosine. The N-terminal amino acid sequences of the antigens were 74.3% homologous among the three strains.

Deficiency of peptidoglycan and lipopolysaccharide components in Rickettsia tsutsugamushi

Analyses of chemical composition in whole cells of Rickettsia tsutsugamushi were performed and compared with those of the other rickettsiae and gram-negative bacteria. The results indicated that R. tsutsugamushi does not contain detectable amounts of 3-deoxy-D-mannooctulosonic acid, heptose, muramic acid, or glucosamine (less than 2, less than 2, less than 3, and less than 3 nmol/mg, respectively). The microorganism was found to contain four kinds of fatty acids (16:0, 18:0, 18:1, and 18:2), but not hydroxy fatty acids. Furthermore, in analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by silver or Coomassie blue staining, lipopolysaccharide bands were not detected in preparations treated with proteinase K. It is concluded that R. tsutsugamushi has little or no peptidoglycan or lipopolysaccharide.

Analysis of polypeptide composition and antigenic components of Rickettsia tsutsugamushi by polyacrylamide gel electrophoresis and immunoblotting

Polyacrylamide gel electrophoresis of lysates of purified Rickettsia tsutsugamushi revealed as many as 30 polypeptide bands, including major bands corresponding to molecular sizes of 70, 60, 54 to 56, and 46 to 47 kilodaltons. Compared with the polypeptide composition of the rickettsiae of Gilliam, Karp, and Kato strains and a newly isolated Shimokoshi strain, the major polypeptide in the Kato strain (54-56K) and in the Karp strain (46-47K) migrated a little faster and slower, respectively, than the corresponding polypeptides in the other strains. The largest major polypeptide (54-56K) was digestible by the treatment of intact rickettsiae with trypsin and variable in content in separate preparations, suggesting that the polypeptide exists on the rickettsial surface and is easily degraded during the handling of these microorganisms. Several surface polypeptides of rickettsiae, including the 54-56K and 46-47K polypeptides, were detected by radioiodination of intact rickettsiae followed by polyacrylamide gel electrophoresis of the lysate; however, the 70K and 60K polypeptides were not labeled. Immunoblotting experiments with hyperimmune sera prepared in guinea pigs against each strain demonstrated that the 70K, 54-56K, and 46-47K polypeptides showed antigenic activities. The 54-56K polypeptide appeared to be strain specific, whereas the 70K and 46-47K polypeptides cross-reacted with the heterologous antisera.