Characterization of the Madrid E strain of Rickettsia prowazekii purified by renografin density gradient centrifugation

Comparison of different media for preservation and transport of viable rickettsiae

Rickettsiae tend to have a rapid decrease of viability outside living cells. Therefore, the transport of samples containing viable rickettsiae for culturing in cell culture for diagnostic purposes is challenging. The viability of rickettsiae in different transport media (commercially available transport medium COPAN "UTM-RT transport medium for viruses, chlamydia, mycoplasma, and ureaplasma," minimal essential medium (MEM) with and without 10% foetal calf serum) at various time points at 4 °C and at ambient temperature (22 °C) was compared. Rickettsia honei was used as model organism. After 2 weeks of storage at room temperature, no viable rickettsiae were detectable any more while storage at 4 °C kept rickettsiae viable for up to 4 weeks. The commercially available COPAN medium showed similarly good or slightly better stabilizing effects on rickettsiae compared with MEM + 10% foetal calf serum, pure MEM demonstrated the poorest results. It is important to transport and store media with potentially rickettsiae-containing samples at 4 °C to prevent inactivation. MEM + 10% foetal calf serum can be used if no commercial medium is available with similarly good results.

Inactivation of rickettsiae

A reliable and complete inactivation is an indispensable premise for any concentration of rickettsiae or for the development of diagnostic strategies based on their antigens. This study deals with the testing of methods to inactivate rickettsiae. Rickettsia honei was used as a model organism. The inactivating potency of formalin, Qiagen® antiviral lysozyme (AVL) buffer, heating to 56 °C, and β-propiolactone was analyzed in cell culture. The inactivation limits for rickettsiae were 0.1% formalin about 10 min, Qiagen AVL buffer about 5 min, 56 °C about 5 min, 0.125% β-propiolactone about 1 h, and 0.0125% β-propiolactone overnight. The interpretation was limited by cytotoxic effects of the inactivation procedures and by the culturally achievable rickettsial density in the cell culture supernatants that were used for the inactivation experiments. Reliable modes of inactivation were identified, allowing for the secure handling of rickettsial antigens for diagnostic purposes.

Insight into the virulence of Rickettsia prowazekii by proteomic analysis and comparison with an avirulent strain

Rickettsia prowazekii, an obligate intracellular Gram-negative bacterium, is the etiologic agent of epidemic typhus. We analyzed the proteome of the virulent Breinl strain of R. prowazekii purified from infected egg yolk sacs. Total proteins from purified R. prowazekii Breinl strain were reduced by dithiothreitol, alkylated by iodoacetic acid and digested with trypsin followed by analysis with an integrated two-dimensional liquid chromatography and mass spectrometry system (2D-LC/MS/MS). A comparison was made using previously analyzed proteome of the Madrid E strain and current analysis of the Breinl strain. For Breinl 251 proteins were identified, representing 30% of the total protein-encoding genes, using a shotgun 2D-LC/MS/MS proteomic approach. This result is identical to that of Madrid E strain. Among the identified proteins, 33 from Breinl and 37 from Madrid E have an unknown function. A methyltransferase, RP028/RP027, whose gene is mutated in the avirulent Madrid E strain but not in the virulent Breinl strain, was only detectable in the Breinl strain, consistent with the genetic mutation in Madrid E. This result suggests the possible relationship between this gene product and the virulence of the strains.

Comparative genomics of Rickettsia prowazekii Madrid E and Breinl strains

Rickettsia prowazekii, the causative agent of epidemic typhus, has been responsible for millions of human deaths. Madrid E is an attenuated strain of R. prowazekii, while Breinl is a virulent strain. The genomic DNA sequence of Madrid E has recently been published. To study the genomic variations between Madrid E (reference) and Breinl (test) DNAs, cohybridization experiments were performed on a DNA microarray containing all 834 protein-coding genes of Madrid E. Of the 834 genes assessed, 24 genes showed 1.5- to 2.0-fold increases in hybridization signals in Breinl DNA compared to Madrid E DNA, indicating the presence of genomic variations in approximately 3% of the total genes. Eighteen of these 24 genes are predicted to be involved in different functions. Southern blot analysis of five genes, virB4, ftsK, rfbE, lpxA, and rpoH, suggested the presence of an additional paralog(s) in Breinl, which might be related to the observed increase in hybridization signals. Studies by real-time reverse transcription-PCR revealed an increase in expression of the above-mentioned five genes and five other genes. In addition to the elevated hybridization signals of 24 genes observed in the Breinl strain, one gene (rp084) showed only 1/10 the hybridization signal of Madrid E. Further analysis of this gene by PCR and sequencing revealed a large deletion flanking the whole rp084 gene and part of the rp083 gene in the virulent Breinl strain. The results of this first rickettsial DNA microarray may provide some important information for the elucidation of pathogenic mechanisms of R. prowazekii.

Transcriptional characterization of the Rickettsia prowazekii major macromolecular synthesis operon

Recent studies have demonstrated that Rickettsia prowazekii can regulate transcription of selected genes at the level of initiation. However, little information concerning the existence of operons and coordinate gene regulation in this obligate intracellular parasitic bacterium is available. To address these issues, we have focused on the rpoD gene linkage group (greA-open reading frame 23 [ORF23]-dnaG-rpoD), which includes the rickettsial analog (ORF23-dnaG-rpoD) of the major macromolecular synthesis operon (MMSO). The rickettsial MMSO consists of an ORF coding for a protein of unknown function the structural genes for DNA primase (dnaG) and the major sigma factor of RNA polymerase (rpoD). RNase protection assays (RPA) were used to determine if these genes are organized into an operon controlled by multiple promoters and the quantities of transcripts produced by these genes relative to each other. RPA with a probe spanning the 270-base greA-ORF23 intervening region identified a putative transcriptional promoter within the intervening sequence. Multiple RPA probes spanning the next 4,041 bases of the linkage group demonstrated the presence of a continuous transcript and thus the existence of an operon. A probe spanning the dnaG-rpoD region revealed that two additional mRNA fragments were also protected, which enabled us to identify additional putative promoters for rpoD within dnaG. Primer extension determined that the 5' ends of the three transcripts consist separately of adenine (located 227 bases upstream of ORF23) and uracil and adenine (located 336 and 250 bases upstream of rpoD, respectively). Quantitation of transcripts produced by the three ORFs determined the relative amounts of transcripts (ORF23 to dnaG to rpoD) to be 1:2.7:5.1.

Organization of Wolbachia pipientis in the Drosophila fertilized egg and embryo revealed by an anti-Wolbachia monoclonal antibody

Cytoplasmic incompatibility (CI) in Drosophila is related to the presence of Wolbachia, an intracellular microorganism found in many species of insects. In order to study the intracellular localization of Wolbachia in eggs and embryos, we have purified the bacteria from fly embryos and subsequently generated a monoclonal antibody (Mab Wol-1) specific for Wolbachia. Indirect immunofluorescence staining using Wol-1 reveals that during mitosis, Wolbachia are localized near spindle poles and centrosomes. Double label immunofluorescence experiments using anti-tubulin and anti-Wolbachia antibodies show that Wolbachia co-localize with centrosomal microtubules throughout the cell cycle. Direct interactions between the bacteria and centrosome-organized microtubules are implied from seven observations: (1) throughout the mitotic cycle, the position and movement of Wolbachia precisely mimic the behavior of the centrosome and apparently associated with centrosome-organized microtubules; (2) Wolbachia segregate equally to each spindle pole during mitosis; (3) Wolbachia do not associate with spindle microtubules during mitosis; (4) Wolbachia located in the egg cortex localize to the domains of cytoplasm organized by microtubules during blastoderm formation; (5) polar body nuclei that lack centrosomes but contain associated microtubules do not contain Wolbachia; (6) Wolbachia no longer associated with yolk nuclei, following differentiation and loss of centrosomes; (7) during pole cell formation, Wolbachia co-localize with the centrosome on the apical side of the nucleus as pole cells form. Quantitative data indicates that no Wolbachia growth occurs during the preblastoderm period even though rapid nuclear, and subsequent cellular, proliferation takes place during this same period. This indicates that Wolbachia are under strict growth regulation by the host suggesting that host factors play a role in regulating growth of Wolbachia in the egg. Further cellular and molecular studies of the extensive, global interactions between host and symbiont observed in this egg should provide important new insights into the evolution of host/symbiosis and the cell biology of cytoplasmic incompatibility.

Detection of mip-like sequences and Mip-related proteins within the family Rickettsiaceae

The Mip surface protein, a prokaryotic analog of the FK506-binding proteins, enhances the ability of Legionella pneumophila to infect macrophages and protozoa. Using mip-specific probes and low-stringency Southern hybridizations, we have detected DNA sequences homologous to mip within Coxiella burnetii and Rochalimaea quintana. Using specific anti-Mip antisera and immunoblot analysis, we also detected Mip-related proteins within these bacteria as well as within Rickettsia and Ehrlichia species. These data suggest that Mip-related proteins have broad significance for host-parasite interactions. However, they also indicate that care must be exercised when using mip probes or anti-Mip antibodies for the detection of Legionella organisms in water or clinical samples.

The concentrations of stable RNA and ribosomes in Rickettsia prowazekii

The obligate intracellular parasite, Rickettsia prowazekii, is a slow-growing bacterium with a doubling time of about 10 h. In the present study, DNA and RNA were obtained from the rickettsiae by two independent methods, i.e. simultaneous isolation of DNA and RNA from the same sample by phenol:chloroform extraction and CsCI gradient centrifugation. In addition, ribosomal RNA was obtained by sedimentation of partially purified ribosomes from the rickettsiae. The results demonstrated that, after correction for the cell volumes, the concentrations of stable RNA and ribosomes in R. prowazekii, a slow-growing organism, were about 62 fg micron-3 and 17,000 per micron3, respectively, which were very similar (66 fg micron-3 and 21,000 per micron3) to those in Escherichia coli with a generation time of 40 min. However, on a per cell basis, R. prowazekii had 5.6 fg of RNA and 1500 ribosomes per cell, which was only about 8% of the amount of both stable RNA (71.2 fg) and ribosomes (24,000) per cell as was found in E. coli. These results indicated that R. prowazekii possesses a ribosome concentration greater than might have been predicted from its slow growth rate. This high concentration of ribosomes could be due to a large population of nonfunctioning ribosomes, a low efficiency of amino acid production, or a high rate of protein turnover. However, this study also demonstrated that the rickettsiae have very limited protein turnover. Knowledge of the kinetics and control mechanisms for protein synthesis in R. prowazekii remains to be established to determine the logic of the extra rickettsial ribosomes.

Analysis of the peptidoglycan of Rickettsia prowazekii

In the present study, peptidoglycan from Rickettsia prowazekii, an obligate intracellular bacterium, was purified. The rickettsial peptidoglycan is like that of gram-negative bacteria; that is, it is sodium dodecyl sulfate insoluble, lysozyme sensitive, and composed of glutamic acid, alanine, and diaminopimelic acid in a molar ratio of 1.0:2.3:1.0. The small amount of lysine found in the peptidoglycan preparation suggests that a peptidoglycan-linked lipoprotein(s) may be present in the rickettsiae. D-Cycloserine, a D-alanine analog which inhibits the biosynthesis of bacterial cell walls, prevented rickettsial growth in mouse L929 cells at a high concentration and altered the morphology of the rickettsiae at a low concentration. These effects were prevented by the addition of D-alanine. This suggests that R. prowazekii contains D-alanine in the peptidoglycan and has D-Ala-D-Ala ligase and alanine racemase activities.

Copy number of the 16S rRNA gene in Rickettsia prowazekii

The obligate intracellular parasite, Rickettsia prowazekii, is a slowly growing bacterium with a doubling time of 8 to 12 h. The copy number of the 16S rRNA gene in the rickettsial chromosome was determined to be one. Genomic DNA from R. prowazekii was digested either by a variety of restriction enzymes known not to cut at any site in the rickettsial 16S rRNA gene or by a combination of these noncutting enzymes and SmaI, which cuts the gene only once. Only one DNA fragment in these digests hybridized to a biotinylated probe containing a portion of the rickettsial 16S rRNA gene. Moreover, the density of the rickettsial 16S rRNA gene fragment after hybridization was equal to the density of each of the seven 16S rRNA gene fragments in Escherichia coli.

Purification of Cytoecetes phagocytophila, the causative agent of tick-borne fever, from infected ovine blood

Cytoecetes phagocytophila, the causative agent of tick-borne fever, was successfully separated by Percoll and Renografin density gradient centrifugation and by cellular affinity chromatography, from the peripheral blood leucocytes of experimentally infected sheep. After centrifugation on Renografin or Percoll density gradients, infectious particles of C. phagocytophila banded at buoyant densities which ranged between 1.063 to 1.140. Rickettsiae separated by wheat germ lectin cellular affinity chromatography retained their morphology but often lost their infectivity. Cell-free C. phagocytophila remained infective to susceptible sheep for 6 months when kept at -114 degrees C in sucrose phosphate buffer with 10 per cent dimethylsulphoxide as a cryopreservative.

Reduction of ribonucleotides by the obligate intracytoplasmic bacterium Rickettsia prowazekii

Rickettsia prowazekii, an obligate intracellular parasitic bacterium, was shown to have a ribonucleotide reductase that would allow the rickettsiae to obtain the deoxyribonucleotides needed for DNA synthesis from rickettsial ribonucleotides rather than from transport. In the presence of hydroxyurea, R. prowazekii failed to grow in mouse L929 cells or SC2 cells (a hydroxyurea-resistant cell line), which suggested that R. prowazekii contains a functional ribonucleotide reductase. This enzymatic activity was demonstrated by the conversion of ADP to dADP and CDP to dCDP, using (i) a crude extract of Renografin-purified R. prowazekii that had been harvested from infected yolk sacs and (ii) high-performance liquid chromatographic analysis. The rickettsial ribonucleotide reductase utilized ribonucleoside diphosphates as substrates, required magnesium and a reducing agent, and was inhibited by hydroxyurea. ADP reduction was stimulated by dGTP and inhibited by dATP. CDP reduction was stimulated by ATP and adenylylimido-diphosphate and inhibited by dATP and dGTP. These characteristics provided strong evidence that the rickettsial enzyme is a nonheme iron-containing enzyme similar to those found in mammalian cells and aerobic Escherichia coli.

Purification and partial characterization of the DNA-dependent RNA polymerase from Rickettsia prowazekii

The DNA-dependent RNA polymerase was purified from Rickettsia prowazekii, an obligate intracellular bacterial parasite. Because of limitation of available rickettsiae, the classical methods for isolation of the enzyme from other procaryotes were modified to purify RNA polymerase from small quantities of cells (25 mg of protein). The subunit composition of the rickettsial RNA polymerase was typical of a eubacterial RNA polymerase. R. prowazekii had beta' (148,000 daltons), beta (142,000 daltons), sigma (85,000 daltons), and alpha (34,500 daltons) subunits as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The appropriate subunits of the rickettsial RNA polymerase bound to polyclonal antisera against Escherichia coli core polymerase and E. coli sigma 70 subunit in Western blots (immunoblots). The enzyme activity was dependent on all four ribonucleoside triphosphates, Mg2+, and a DNA template. Optimal activity occurred in the presence of 10 mM MgCl2 and 50 mM NaCl. Interestingly, in striking contrast to E. coli, approximately 74% of the rickettsial RNA polymerase activity was associated with the rickettsial cell membrane at a low salt concentration (50 mM NaCl) and dissociated from the membrane at a high salt concentration (600 mM NaCl).

The line blot: an immunoassay for monoclonal and other antibodies. Its application to the serotyping of gram-negative bacteria

A procedure is described for assaying antibodies based on the application of antigen to nitrocellulose as a line with an ink pen point. The method requires no expensive apparatus, is easy to perform, and requires less than 0.25 micrograms of antigen per assay. More than 45 antigens can be assayed simultaneously with a single antibody. Antigens can be applied as purified proteins, extracts, or sodium dodecyl sulfate solubilized extracts. The application of the line blot assay for the detection of monoclonal antibodies which recognize heat-sensitive and insensitive epitopes on the typhus rickettsia surface protein antigen is described. A new serotyping assay for Gram-negative bacteria is also described in which sodium dodecyl sulfate solubilized antigens are applied as lines with and without prior proteinase K digestion. The value of the line blot serotyping assay is demonstrated with Proteus. Rickettsia, Rochalimaea, and Legionella antigens. The line blot immunoassay is a simple, but powerful and flexible, alternative to dot and cross-dot immunoassays.

Phylogenetic diversity of the Rickettsiae

Small subunit rRNA sequences have been determined for representative strains of six species of the family Rickettsiaceae: Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia typhi, Coxiella burnetii, Ehrlichia risticii, and Wolbachia persica. The relationships among these sequences and those of other eubacteria show that all members of the family Rickettsiaceae belong to the so-called purple bacterial phylum. The three representatives of the genus Rickettsia form a tight monophyletic cluster within the alpha subdivision of the purple bacteria. E. risticii also belongs to the alpha subdivision and shows a distant yet specific relationship to the genus Rickettsia. However, the family as a whole is not monophyletic, in that C. burnetii and W. persica are members of the gamma subdivision. The former appears to show a specific, but rather distant, relationship to the genus Legionella.

Recognition of typhus group rickettsia-infected targets by human lymphokine-activated killer cells

Lymphokine-activated killer cells caused significant lysis of target cells infected with typhus group rickettsiae (TGR) but not cells infected with Rickettsia tsutsugamushi. Monoclonal and polyclonal antibodies against TGR or TGR-infected cells failed to bind specifically to infected targets, as determined by flow cytometry or by immunoprecipitation of radiolabeled cell surface proteins. Major unaltered antigenic determinants of TGR therefore cannot be detected on the surface of infected targets.

Purification of Rickettsia tsutsugamushi by Percoll density gradient centrifugation

Purification of Rickettsia tsutsugamushi has been achieved by Percoll density gradient centrifugation. The microorganisms purified showed good retention of infectivity and intracellular morphology. Budding rickettsiae in the egressing stage and intracellular rickettsiae in the multiplying process were harvested separately and purified by this technique. In electron microscopic observations, the intracellular rickettsiae obtained were surrounded with double membrane-layers of cell wall and cell membrane, and the budding rickettsiae were enveloped with an additional outermost membrane which may have originated from host cell membrane obtained in the budding process.

Some characteristics of heavy and light bands of Rickettsia prowazekii on Renografin gradients

Suspensions of partially purified Rickettsia prowazekii yielded two bands of organisms when centrifuged to equilibrium in Renografin density gradients. Rickettsiae from the lower, heavy band were defective in their infective and metabolic activities, as compared to organisms from the light band. The greater density in Renografin of heavy-banding organisms was due to their lack of permeability barrier to it, as evidenced by the absence of plasmolysis in hypertonic Renografin. In contrast, light-banding rickettsiae were able to exclude Renografin, since they were plasmolyzed in it. The proportion of heavy-banding organisms in a rickettsial suspension was influenced by the growth phase they were in when harvested from infected yolk sacs, as well as by the conditions and media to which they subsequently were exposed. We have concluded that these defective forms arise from the degeneration of light-banding rickettsiae. This separation of two functional classes of rickettsiae in Renografin density gradients has been exploited (i) to increase the uniformity of the suspensions by removing many noninfectious particles and (ii) to determine rapidly the integrity of certain properties of the cytoplasmic membrane of organisms exposed to a variety of conditions.

Isolation of species-specific protein antigens of Rickettsia typhi and Rickettsia prowazekii for immunodiagnosis and immunoprophylaxis

A simple procedure for the selective isolation of the protective species-specific protein antigens (SPAs) of Rickettsia typhi and Rickettsia prowazekii was developed to permit use of the SPAs in the immunodiagnosis and immunoprophylaxis of typhus infections. Although the SPAs were readily extracted from lysozyme- or detergent-treated rickettsiae, as measured by rocket immunoelectrophoresis, other polypeptides were also present, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In contrast, both water and seven buffers, each at a 10 mM concentration and pH 7.6, were nearly equally effective in the selective release of the SPAs from whole cells by extraction for 30 min at 45 degrees C. High-ionic-strength buffers and MgCl2 abolished this SPA release, thus suggesting that divalent cations were important in the binding of the SPAs to the cell envelope. The efficacy of the dilute buffer extraction procedure for isolation of large amounts of SPAs was tested by further characterization of the supernatants obtained by centrifugation (200,000 x g) of two successive tris-(hydroxymethyl)aminomethane-hydrochloride buffer (Tris) extracts. With this procedure, between 10 and 15 mg of SPA was obtained from 100 mg of purified rickettsiae. Although low-molecular-weight ribonucleic acid fragments were released into the Tris extracts in significant amounts, only the SPAs were detected, in significant quantities, as measured by polyacrylamide gel electrophoresis and rocket immunoelectrophoresis. The Tris extracts contained the same major and minor SPA polypeptides as those observed previously in SPA preparations obtained by extensive diethylaminoethyl-cellulose column chromatography, but the Tris SPAs were more satisfactory antigens in an enzyme-linked immunosorbent assay.

Immunological and biological characterization of Coxiella burnetii, phases I and II, separated from host components

Coxiella burnetii, phase I and II, cells cultivated in the yolk sac of chicken embryos were separated from host cell components by two cycles of isopycnic Renografin gradient centrifugation. Initial steps in the purification of viable C. burnetii involved differential centrifugation and sedimentation through an aqueous solution of 30% sucrose and 7.6% Renografin. After the first, but not the second, cycle of Renografin gradient centrifugation, the cells were passed through microfilter glass filters which facilitated the removal of host components. The integrity of morphologically different cell variants was maintained during purification procedures by suspending highly purified C. burnetii in phosphate-buffered saline-sucrose solutions. C. burnetii, phases I and II, obtained by these methods appeared to be free from host cell components by serological methods while retaining morphological integrity and infectivity for yolk sacs and experimental animals. Average yields of C. burnetii were 2.83, 1.5, and 0.84 mg (dry weight) per yolk sac of the Ohio strain (phase I), 9 Mile strain (phase I), and 9 Mile strain (phase II), respectively. Recovery of phase I cells averaged about 70%, whereas the recovery of phage II cells was approximately 40%. The temporal sequence of phase I and II antibody response was demonstrated in infected and vaccinated animals. Also, no antibody response in mice and guinea pigs to yolk sac antigens was detectable after two injections of vaccine or viable cells. Importantly, this is the first report of the separation of viable phase II cells of C. burnetii free of host components.

Partial purification and characterization of the major species-specific protein antigens of Rickettsia typhi and Rickettsia prowazekii identified by rocket immunoelectrophoresis

Species-specific antigens from Rickettsia typhi and Rickettsia prowazekii were readily solubilized by French pressure cell extraction or sonication of Renografin density gradient-purified rickettsiae and were identified by rocket immunoelectrophoresis. As measured by quantitative rocket immunoelectrophoresis, the species-specific typhus rocket antigens (STRAs) appeared to be proteins; they were denatured by heating at 56 degrees C for 30 min but not by 50 degrees C treatment, and they were sensitive to pronase and trypsin but were not affected by periodate oxidation, glycosidases of various specificities, phospholipase A, or lipase. STRAs from both R. typhi and R. prowazekii were separated from common antigens by DE52 column chromatography of 100,000-X-g supernatant fractions of rickettsial extracts. The purified STRAs were characterized by crossed immunoelectrophoresis, by polyacrylamide gel electrophoresis on Davis and sodium dodecyl sulfate gels, and by an enzyme-linked immunosorbent assay. The two purified STRAs were proteins with similar native electrophoretic mobilities in agarose and polyacrylamide gels, and these proteins had similar polypeptide patterns on sodium dodecyl sulfate gels. Most of the STRA activity migrated as a single protein band on sodium dodecyl sulfate-polyacrylamide and Davis polyacrylamide gels, although minor protein bands with STRA activity were also detected. The major STRA proteins constituted 10 to 15% of the total cellular protein of R. typhi and R. prowazekii. According to sensitive enzyme-linked immunosorbent assay titrations, the STRA of R. prowazekii had substantial cross-reactivity with rabbit antiserum prepared against R. typhi, as shown also by rocket immunoelectrophoresis, whereas the STRA of R. typhi reacted only very weakly with antiserum prepared against R. prowazekii according to the enzyme-linked immunosorbent assay and not at all according to rocket immunoelectrophoresis.

Phospholipase A activity in the hemolysis of sheep and human erythrocytes by Rickettsia prowazeki

Incubation of Rickettsia prowazeki with sheep or human erythrocytes resulted in lysis of the erythrocytes and formation of free fatty acids and lysophosphatides. Inhibitors of lysis were also invariably inhibitors of this phospholipase A activity. The target for this activity was the glycerophospholipids of the erythrocyte and not those of the rickettsia. Rickettsial phosphatidylethanolamine labeled with (32)PO(4) or [(3)H]acetate remained intact during lysis, and the composition of the free fatty acids released resembled that of the erythrocyte species used and not the rickettsiae. The products of hydrolysis remained associated with the sedimentable material in the reaction mixture under the usual conditions but partitioned into the supernatant fluid when bovine serum albumin was present. Initially, the time course of phospholipase A activity and lysis was identical, but the release of free fatty acids continued for a short time after the release of hemoglobin was complete. Both the inner and outer leaflets of the erythrocyte membrane were accessible to this rickettsial phospholipase A activity since both phosphatidylcholine and phosphatidylethanolamine were substrates in human erythrocytes. The questions of whether rickettsiae possess their own phospholipase A or activate a latent erythrocyte enzyme and what the role of the energy requirement is in these processes remain unanswered.

In vitro stimulation of human peripheral blood lymphocytes by soluble and membrane fractions of renografin-purified typhus group rickettsiae

Cell-free extracts of disrupted Renografin-purified Rickettsia typhi and R. prowazekii were evaluated as antigens in lymphocyte transformation assays for cell-mediated immunity to typhus group rickettsiae in 19 individuals with and 9 without histories of exposure to these organisms. Exposure consisted of clinical disease, vaccination with epidemic typhus vaccine, or occupational exposure to these agents. Both the soluble and membrane fractions of disrupted purified rickettsiae were used, and transformation of peripheral blood lymphocytes (PBL) was determined in microcultures by incorporation of [(3)]thymidine. Of the antigen concentrations tested (1 to 400 mug/ml), 10mug/ml appeared to be the most satisfactory. At this concentration, PBL transformation was highly reproducible and correlated well with donor exposure and the presence of enzyme-linked immunosorbent assay anti-typhus group immunoglobulin G. At higher concentrations, PBL from both exposed and control donors often responded to a lipopolysaccharide-like component present in these preparations. Specific transformation responses to rickettsial fractions were detected in several individuals decades after infection or vaccination, indicating that both fractions contained antigens associated with persisting cell-mediated immunity in humans. Generally, stimulation indexes with the soluble fraction were slightly greater than those obtained with corresponding concentrations of the membrane preparation, and in three individuals transformation was observed only with the soluble fraction. PBL transformation to soluble fractions also appeared to have some species specificity, since PBL from individuals with documented R. typhi infections were more responsive to the homologous soluble preparation than to the soluble fraction of R. prowazekii. PBL transformation also correlated well with homologous but only poorly with heterologous enzyme-linked immunosorbent assay immunoglobulin G titers.

Sensitive microplate enzyme-linked immunosorbent assay for detection of antibodies against the scrub typhus rickettsia, Rickettsia tsutsugamushi

A microtiter enzyme-linked immunosorbent assay (ELISA) has been developed for the titration of antibodies against scrub typhus in human and animal sera. Scrub typhus rickettsiae were grown in monolayers of irradiated mouse LM3 cells and separated from host cell materials by differential centrifugation, filtration through a glass filter (AP-20, Millipore Corp.), and isopycnic banding in Renografin density gradients. The scrub typhus ELISA antigens were obtained from the purified viable rickettsiae by French pressure cell disruption and addition of 0.2% Formalin to the soluble extract. Antisera prepared in rabbits against the prototype Karp, the Kato, and the Gilliam strains of scrub typhus were used to standardize the ELISA and to compare its sensitivity and specificity to that of the indirect fluorescent antibody test (IFA). ELISA titers were measured as the greatest serum dilution showing an optical density 0.25 above controls or by the optical density achieved at a fixed serum dilution. The IFA and ELISA end point titers were quite similar, and all three measures of titer had comparable specificity for the strains of scrub typhus. No cross-reactions between the typhus and scrub typhus wera were observed by ELISA. Both the immunoglobulin M (IgM) and IgG antibody titers of 12 sequential sera from four patients with scrub typhus were obtained by IFA and ELISA. The IFA and ELISA end point titers for IgM and IgG had correlation coefficients of 0.91 and 0.97, respectively, whereas the ELISA optical density values at a serum dilution of 1:100 had slightly lower correlations with IFA titers (0.80 and 0.94). Early rising IgM titers followed by rising IgG titers were demonstrated by ELISA in three patients with primary scrub typhus infections, whereas the IgG response predominated in a patient with a reinfection. It is concluded that the ELISA for scrub typhus is a very satisfactory alternative to the IFA test.

Synthesis of DNA and protein by Anaplasma marginale in bovine erythrocytes during short-term culture

Bovine erythrocytes infected with Anaplasma marginale were cultured for 1 to 5 days in a CO2 incubation chamber, pulse-labeled with [3H]thymidine and [14C]methionine, lysed, and fractionated by differential centrifugation and continuous density gradient centrifugation in Renografin. Anaplasma and associated fragments of stroma formed two distinct bands in the dense region of the gradient. Electron microscopic examination of pelleted material from the bands from cells cultured for 1 day revealed the presence of organisms that were morphologically intact or in various states of degeneration. Examination of fractions from the gradient for incorporation of label revealed that analplasma present in erythrocytes can incorporate both [3H]thymidine and [14C]methionine. Subsequent experiments demonstrated that organisms cultured for 3 and 5 days incorporated the radiolabeled compounds also, but to a lesser extent. The experiments demonstrate that it is possible to culture analplasma in vitro for short periods of time and monitor their growth characteristics.

Phospholipid composition of Rickettsia prowazeki grown in chicken embryo yolk sacs

The phospholipid composition and phospholipid fatty acid composition of purified Rickettsia prowazeki were determined. The lipid phosphorous content was 6.8 +/- 1.3 microgram/mg of total rickettsial protein. The major phospholipid was phosphatidylethanolamine (60 to 70%); phosphatidylglycerol constituted 20%, and phosphatidylcholine constituted 15%. Small amounts of phosphatidylserine and cardiolipin were detected. The principal fatty acids were 18:1, 16:1, and 16:0. The fatty acid composition of the phosphatidylcholine in the rickettsial extracts was very different than that of the other rickettsial phosphatides and very similar to that of normal yolk sac phosphatidylcholine. The specific of the phosphatidylcholine of rickettsiae grown in the presence of 32P was markedly lower than that of phosphatidylethanolamine and phosphatidylglycerol. It is suggested that the phosphatidylcholine in the rickettsial extract is yolk sac derived and either tightly absorbed or exchanged into the rickettsial membrane.

Surface proteins of typhus and spotted fever group rickettsiae

Six proteins, previously established as major constituents of intact organisms, were identified in cell envelopes obtained from intrinsically radiolabeled Rickettsia prowazekii. Extrinsic radioiodination of intact organisms conducted at 0.5 micronM iodide indicated that protein 4 was the most peripheral, although protein 1 also had reactive groups exposed on the surface of the organisms. A 10-fold increase in iodide concentration resulted in labeling of protein 2, and at 50 micronM iodide, all six major proteins were radiolabeled. Similar selective labeling was not achieved with R. conorii. Analysis of both typhus and spotted fever group organisms radiolabeled with galactose suggested that carbohydrate was associated with proteins 1, 3, and 4. Typhus soluble antigen included all major proteins except protein 2, which remained attached to particulate rickettsiae after ether extraction. Protein 4 appeared to be prominent in the surface topography of R. prowazekii, was a component of soluble antigen and may have an important role in rickettsiae-host interactions.

Biochemical characteristics of typhus group rickettsiae with special attention to the Rickettsia prowazekii strains isolated from flying squirrels

Six strains of Rickettsia prowazekii, two derived from human infections and four isolated from flying squirrels, two strains of R. typhi, and the single available strain of R. canada, were characterized by several biochemical procedures. The electrophoretic patterns on polyacrylamide gels of rickettsial proteins solubilized by sodium dodecyl sulfate revealed several species differences, but strains of the same species appeared to have identical patterns. Cytoplasmic fractions of the rickettsiae were examined for enzymatic activities and for polyacrylamide gel isoelectric focusing patterns. Some species differences were encountered in the activities or ratios of activities of glutamate-oxaloacetate transaminase, glutamate dehydrogenase, and malate dehydrogenase. When polyacrylamide gels were stained for malate dehydrogenase after electrophoresis, a single band became apparent with single extracts or mixtures of two strains of R. prowazekii, but two bands were seen with mixtures of a strain of R. prowazekii and one of R. typhi. The isoelectric focusing patterns of the soluble proteins revealed numerous species differences, especially between R. canada and the other two species, and a few differences among the strains of R. prowazekii. The patterns of the two human strains, Breinl and E(R), differed in at least one location, and both differed from the flying squirrel strains in the displacement of one band. One of the flying squirrel strains, GvF-16, contained a protein band not seen in the other five strains. Despite these minor differences, a striking similarity was revealed by all the biochemical tests performed between the R. prowazekii strains of human and flying squirrel origin.

Sensitive enzyme-linked immunosorbent assay for detection of antibodies against typhus rickettsiae, Rickettsia prowazekii and Rickettsia typhi

An enzyme-linked immunosorbent assay (ELISA) has been developed for the titration of rickettsial antibodies in human and animal sera. Two preparations of soluble typhus-group antigens were obtained from Rickettsia typhi and Rickettsia prowazekii by ether extraction: a standard antigen from infected yolk sacs (YS antigen) and one free of yolk sac contaminants from Renografin-purified rickettsiae (PR antigen). Rabbit, mouse, and guinea pig sera were obtained by immunization with viable purified R. typhi or R. prowazekii. Human sera were obtained from individuals who had recovered from laboratory infections with either typhus rickettsia months or years previously. Goat-derived anti-immunoglobulins were conjugated to alkaline phosphatase with glutaraldehyde. Although the PR and YS antigens gave equivalent antibody titers in the complement fixation test, the PR antigen was clearly superior in the ELISA. With this antigen, the titration curves of all antisera were linear over a wider range of serum concentrations and the titers were higher than with the YS antigen. With YS and PR antigens, ELISA titers were higher than those obtained by complement fixation by one and two orders of magnitude, respectively. In human sera, immunoglobulin G and immunoglobulin M antibodies were demonstrated by their respective anti-immunoglobulins and by differential susceptibility to ethanethiol. ELISA titers showed some type specificity, whereas none was observed in complement fixation tests. The ELISA is highly sensitive, reproducible, and easily adaptable to the various requirements of clinical and research laboratories.

Biological properties of Rickettsia prowazekii strains isolated from flying squirrels

Four strains of Rickettsia prowazekii, isolated from flying squirrels (Glaucomys volans volans) from Florida and Virginia, were compared with other strains of the typhus biotype, two previously established strains each of R. prowazekii and R. typhi and one strain of R. canada, for similarities in a number of unrelated phenotypic characteristics. R. akari served as a spotted fever biotype control. All strains produced small plaques on chicken embryo cell monolayers that were clearly recognized only after 10 days of incubation at 32 degrees C. All strains were highly susceptible to erythromycin. The Renografin density gradient centrifugation procedure of separating rickettsiae from the infected yolk sacs of surviving chicken embryos was equally satisfactory in all cases and resulted in moderate to large yields of purified rickettsiae. There was relatively small variation in specific hemolytic activity or specific CO(2) formation from glutamate. None of the strains catabolized glucose. There was some strain variation in virulence for the chicken embryo, but none of the above tests separated the three species of the typhus biotype. On the other hand, R. akari was clearly distinguished by its more rapid plaque formation and by higher resistance to erythromycin. It is concluded that by the tests conducted thus far, the biological properties of the flying squirrel strains do not differ substantially from those of other strains of the typhus biotype.