Kontinuierliche Vermehrung von Coxiella burnetii durch persistierende Infektion in Buffalo-Green-Monkey-(BGM)-Zellkulturen

Coxiella burnetii plasmid types QpDG and QpH1 are closely related and likely identical

Strains and isolates of Coxiella burnetii, an obligate intracellular bacterium, carry a single plasmid or a plasmid-homologous sequence integrated into the chromosome. The plasmids QpH1, QpRS, QpDV and the chromosome-integrated plasmid-homologous region have been completely sequenced, whereas no sequence data are available for the QpDG plasmid. In this study, we used total genomic DNA from reference strain C. burnetii Dugway 5J108-111 to demonstrate and characterize the QpDG plasmid by pulsed-field gel electrophoresis (PFGE) and Southern hybridization. Primers derived from regions shared among C. burnetii plasmids were used to construct a physical map of the QpDG plasmid by extra long (XL) PCR. Both approaches, Southern hybridization and XL PCR indicated that QpDG and QpH1 represent a closely related and likely identical plasmid.

Infection of Vero cells with Coxiella burnetii phase II: relative intracellular bacterial load and distribution estimated by confocal laser scanning microscopy and morphometry

Coxiella burnetii, the agent of Q fever in man and of coxiellosis in other species, is an intracellular pathogen not yet grown axenically. Confocal laser fluorescence microscopy and morphometry were used to measure relative C. burnetii phase II loads and their intracellular distribution in aldehyde fixed and DAPI stained Vero cell monolayers. The fluorescence of single horizontal optical sections provided useful information on relative loads of bacteria in cells and vacuoles. The relative density of the bacteria in the vacuoles was inferred from ratios of fluorescence to vacuolar section areas. Relative bacterial loads, bacterial densities and section areas of large vacuoles increased exponentially between days 2 and 4 of the infection of gamma-irradiated host cells, stabilized between days 4 and 6, and decreased thereafter. Estimated minimum doubling times were higher for the overall complement of the intracellular organisms (about 12 h) than for bacteria that were confined to larger vacuoles (about 10 h).

Sequencing and characterization of the cryptic plasmid QpRS from Coxiella burnetii

Plasmid QpRS from Coxiella burnetii, isolate Priscilla Q177, phase I, has been completely sequenced. DNA for sequencing was amplified with "extra-long" (XL) PCR. The size of the QpRS plasmid sequence was determined to be 39,280 bp, with a G + C content of 39.3%. Putative proteins associated with replication and recombination were identified. The sequence of QpRS plasmid was analyzed for shared and unique regions among C. burnetii plasmids.

A sporulation gene in Coxiella burnetii?

During a search for conserved target sequences on the genome of Coxiella burnetii for a diagnostic PCR a NotI/EcoRV DNA fragment was cloned and sequenced from the isolate "Nine Mile", Phase I (sequence data are registered under accession number X70045 in data bases EMBL, GENEBANK and DDBJ). On this fragment we have found a sequence of 1741 base pairs which showed an exceptionally high homology (60% on the nucleic acid level and 49.6% on the amino acid level) to the sporulation gene "spoIIIE" of the gram-positive bacterium Bacillus subtilis. This is first evidence of the molecular basis for formation of spores in Coxiella burnetii which has been postulated in the literature by electron microscopic investigations.

Titration of Coxiella burnetii in Buffalo green monkey (BGM) cell cultures

Titration of Coxiella burnetii, strain Nine Mile, phase I, and strain Frankfurt, phase II, in Buffalo green monkey (BGM) cover slip cell cultures yielded reproducible infectivity titers after centrifugation of infected cell cultures (3000 g, 30 min, 37 degrees C) and a subsequent 4-day incubation at 37 degrees C in Minimal Essential Medium (MEM). Compared to other titration procedures (plaque assays, titration in embryonated chicken eggs), this technique proved to be fast, less laborious and economical.

Detection of Coxiella burnetii by the immunoperoxidase technique

An immunoperoxidase method using Coxiella (C.) burnetii-specific hyperimmune serum raised in rabbits, and swine anti-rabbit horseradish peroxidase conjugate was applied to visualize C. burnetii in BGM cell cultures. The technique proved to be highly specific and did not result in any unspecific background staining. The technique was applied successfully to study the organism during multiplication in vacuoles of epithelial cells and in the phagolysosomes of macrophages. Preliminary results further indicate that the technique may be useful for the detection of the pathogen in tissues and milk samples.

Q fever vaccines for animals

The results of different workgroups and those obtained in own investigations with Q fever vaccines for cattle and sheep are reviewed and discussed. In field trials Coxiella (C.) burnetii vaccines of inactivated whole cells (WC) in phase (ph) I as well as WC ph II vaccines prevented infections of cows exposed to naturally infected environments, provided they were vaccinated as noninfected calves. To monitor calves for this purpose the sensitive ELISA has superseded the complement fixation test (CF). WC ph I vaccines failed to prevent shedding by uninfected cattle and sheep which were vaccinated and subsequently challenged by parenteral inoculation with viable organisms, but reduced shedding, and prevented pathological lesions and clinical symptoms. The results obtained in field trials with a commercially available vaccine consisting of killed WC ph II of C. burnetii and inactivated WC of Chlamydia psittaci indicated that vaccination had significantly improved fertility in vaccinated herds. However, the mechanism of protection is unclear because the function of the chlamydial component in this vaccine is not yet defined. Cattle given this vaccine can be distinguished from naturally infected cattle because the former produce predominantly non-complement-binding IgG2, detectable by ELISA. This vaccine frequently causes undesirable local reactions. Antigens of C. burnetii (strain "Frankfurt", ph II) prepared by propagation in cell cultures and successive purification by guanidinium hydrochloride- and chloroform/methanol-extraction (CMR), as well as a major protein extracted from these CMR preparations represent potential vaccine candidates without such side effects.

Isolation of a protein antigen from Coxiella burnetii

Antigens prepared from Coxiella burnetti, strain Frankfurt, phase II, propagated in persistently infected Buffalo Green Monkey (BGM) cell cultures were purified by guanidinium hydrochloride treatment and chloroform/methanol extraction. By ELISA analysis, chloroform/methanol residues (CMR) proved to be free of host cell antigens. The CMR were sensitive to trypsin, pronase E and proteinase K, as determined by absorption-kinetics of CMR suspensions at 600 nm and release of protein. Coomassie blue stained SDS polyacrylamide gels of proteinase hydrolysates from CMR revealed only a single component of apparently 27,000 D. Silver stained gels, however, showed a second component of apparently 12,000 D. In contrast, from untreated native C. burnetii a large variety of proteins, most of them protease-sensitive, were released by detergents at low temperatures, but the 27,000 D component was only solubilized at 60-100 degrees C. The 27,000 D component was obviously the major protein of CMR as well as of whole cells. Antigenicity of this 27,000 D protein could be demonstrated by agargel precipitation test, ELISA and immunoperoxidase techniques applying antisera raised against whole cells and against the extracted component. The component was also recognized in a dot immunobinding assay by sera from guinea pigs infected with cloned C. burnetii stain Nine Mile, phase I, thus indicating an important role of this antigen in C. burnetii specific immune response.