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Life cycle, growth characteristics and host cell response of Rickettsia helvetica in a Vero cell line.

ABSTRACT: Rickettsia helvetica, a spotted fever rickettsia and emerging pathogen with Ixodes ricinus ticks as the main vector, is an agent of human disease and may cause febrile illness as well as meningitis. In three parallel series the isolated standard type of R. helvetica, obtained from a PCR-positive I. ricinus tick, was high-passaged and propagated in a Vero cell line. By using quantitative real-time PCR, the generation time from inoculation to stationary phase of growth was calculated to 20-22 h. In the static cultivation system the stationary phase was observed from the seventh day after inoculation, and there was no observed degradation of R. helvetica DNA during the 14 days studied. Microscopy showed that the organisms invaded the host cells rapidly and were primarily found free in the cytoplasm and only occasionally located in the nucleus. Four days after inoculation some of the host cells were broken and many indifferent stages of cytoplasmic organic decomposition were seen. However the R. helvetica organism did not show any morphologic alterations and the number of organisms was stable after the replication peak which may indicate that R. helvetica is adapted to growth in a Vero cell line and/or that the phase of degradation occurs later than the 14 days studied. The findings differ from what has been reported for other rickettsiae of the spotted fever group and may be of importance for invasiveness and virulence of R. helvetica.

SUBMITTER: Elfving K

PROVIDER: S-EPMC3253991 | biostudies-literature |

REPOSITORIES: biostudies-literature

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In vitro studies of Rickettsia-host cell interactions: Confocal laser scanning microscopy of Rickettsia helvetica-infected eukaryotic cell lines.

Project description:Rickettsia (R.) helvetica is the most prevalent rickettsia found in Ixodes ricinus ticks in Germany. Several studies reported antibodies against R. helvetica up to 12.5% in humans investigated, however, fulminant clinical cases are rare indicating a rather low pathogenicity compared to other rickettsiae. We investigated growth characteristics of R. helvetica isolate AS819 in two different eukaryotic cell lines with focus on ultra-structural changes of host cells during infection determined by confocal laser scanning microscopy. Further investigations included partially sequencing of rickA, sca4 and sca2 genes, which have been reported to encode proteins involved in cell-to-cell spread and virulence in some rickettsiae. R. helvetica grew constantly but slowly in both cell lines used. Confocal laser scanning microscopy revealed that the dissemination of R. helvetica AS819 in both cell lines was rather mediated by cell break-down and bacterial release than cell-to-cell spread. The cytoskeleton of both investigated eukaryotic cell lines was not altered. R. helvetica possesses rickA, but its expression is not sufficient to promote actin-based motility as demonstrated by confocal laser scanning microscopy. Hypothetical Sca2 and Sca4 proteins were deduced from nucleotide gene sequences but the predicted amino acid sequences were disrupted or truncated compared to other rickettsiae most likely resulting in non-functional proteins. Taken together, these results might give a first hint to the underlying causes of the reduced virulence and pathogenicity of R. helvetica.

| S-EPMC5825168 | biostudies-literature

Rickettsia helvetica

Project description:Rickettsia helvetica overview

| PRJNA83343 | ENA

Rickettsia helvetica in Dermacentor reticulatus ticks.

Project description:We report on the molecular evidence that Dermacentor reticulatus ticks in Croatia are infected with Rickettsia helvetica (10%) or Rickettsia slovaca (2%) or co-infected with both species (1%). These findings expand the knowledge of the geographic distribution of R. helvetica and D. reticulatus ticks.

| S-EPMC2660705 | biostudies-literature

Rickettsia helvetica in Ixodes ricinus ticks in Sweden.

Project description:In the present study further characterization of the amplified sequence of the citrate synthase gene of the spotted fever group Rickettsia isolated from Ixodes ricinus ticks in Sweden showed that it has 100% homology with the deposited sequence of the citrate synthase gene of Rickettsia helvetica. The restriction fragment length polymorphism (RFLP) pattern of an amplified 382-bp product of the citrate synthase sequence, defined by primers RpCS877 and RpCS1258, yielded fragments for our isolate that could be visualized as a double band that migrated at approximately 44 bp, another double band at 85 bp, and a single band at nearly 120 bp after digestion with the restriction enzyme AluI. When calculating a theoretical PCR-RFLP pattern of the sequence of the citrate synthase gene of R. helvetica from the known positions where the AluI enzyme cuts, we arrived at the same pattern that was obtained for our isolate, a pattern distinctly different from the previously published PCR-RFLP pattern for R. helvetica. Investigation of 125 living I. ricinus ticks showed a higher prevalence of rickettsial DNA in these ticks than we had found in an earlier study. Rickettsial DNA was detected by amplification of the 16S rRNA gene, for which a seminested primer system consisting of two oligonucleotide primer pairs was used. Of the 125 ticks, some were pooled, giving a total of 82 tick samples, of which 20 were found to be positive for the rickettsial DNA gene investigated. When considering the fact that some of the positive samples were pooled, the minimum possible prevalence in these ticks was 20 of 125 (16%) and the maximum possible prevalence was 46 of 125 (36.8%). These prevalence estimates conform to those of other studies of spotted fever group rickettsiae in hard ticks in Europe.

| S-EPMC84320 | biostudies-literature

Rickettsia helvetica in patient with meningitis, Sweden, 2006.

Project description:Pathogenicity of Rickettsia helvetica is relatively unknown. We isolated a spotted fever group rickettsial organism from a patient with subacute meningitis. Nucleotide sequences of the 16S rRNA, ompB, and 17kDa genes identified the isolate as R. helvetica. This organism may be associated with serious infections such as central nervous system disorders.

| S-EPMC3322002 | biostudies-literature

Isolation and Growth Characteristics of SARS-CoV-2 in Vero Cell.

Project description: Not available

| S-EPMC7303940 | biostudies-literature

Rickettsia helvetica C9P9

Project description:Rickettsia helvetica C9P9 Genome sequencing and assembly

| PRJNA82855 | ENA

Characterization and growth of polymorphic Rickettsia felis in a tick cell line.

Project description:Morphological differentiation in some arthropod-borne bacteria is correlated with increased bacterial virulence, transmission potential, and/or as a response to environmental stress. In the current study, we utilized an in vitro model to examine Rickettsia felis morphology and growth under various culture conditions and bacterial densities to identify potential factors that contribute to polymorphism in rickettsiae. We utilized microscopy (electron microscopy and immunofluorescence), genomic (PCR amplification and DNA sequencing of rickettsial genes), and proteomic (Western blotting and liquid chromatography-tandem mass spectrometry) techniques to identify and characterize morphologically distinct, long-form R. felis. Without exchange of host cell growth medium, polymorphic R. felis was detected at 12 days postinoculation when rickettsiae were seeded at a multiplicity of infection (MOI) of 5 and 50. Compared to short-form R. felis organisms, no change in membrane ultrastructure in long-form polymorphic rickettsiae was observed, and rickettsiae were up to six times the length of typical short-form rickettsiae. In vitro assays demonstrated that short-form R. felis entered into and replicated in host cells faster than long-form R. felis. However, when both short- and long-form R. felis organisms were maintained in cell-free medium for 12 days, the infectivity of short-form R. felis was decreased compared to long-form R. felis organisms, which were capable of entering host cells, suggesting that long-form R. felis is more stable outside the host cell. The relationship between rickettsial polymorphism and rickettsial survivorship should be examined further as the yet undetermined route of horizontal transmission of R. felis may utilize metabolically and morphologically distinct forms for successful transmission.

| S-EPMC2394910 | biostudies-literature

Ixodes ricinus ticks are reservoir hosts for Rickettsia helvetica and potentially carry flea-borne Rickettsia species.

Project description:BACKGROUND:Hard ticks have been identified as important vectors of rickettsiae causing the spotted fever syndrome. Tick-borne rickettsiae are considered to be emerging, but only limited data are available about their presence in Western Europe, their natural life cycle and their reservoir hosts. Ixodes ricinus, the most prevalent tick species, were collected and tested from different vegetation types and from potential reservoir hosts. In one biotope area, the annual and seasonal variability of rickettsiae infections of the different tick stages were determined for 9 years. RESULTS:The DNA of the human pathogen R. conorii as well as R. helvetica, R. sp. IRS and R. bellii-like were found. Unexpectedly, the DNA of the highly pathogenic R. typhi and R. prowazekii and 4 other uncharacterized Rickettsia spp. related to the typhus group were also detected in I. ricinus. The presence of R. helvetica in fleas isolated from small rodents supported our hypothesis that cross-infection can occur under natural conditions, since R. typhi/prowazekii and R. helvetica as well as their vectors share rodents as reservoir hosts. In one biotope, the infection rate with R. helvetica was ~66% for 9 years, and was comparable between larvae, nymphs, and adults. Larvae caught by flagging generally have not yet taken a blood meal from a vertebrate host. The simplest explanation for the comparable prevalence of R. helvetica between the defined tick stages is, that R. helvetica is vertically transmitted through the next generation with high efficiency. The DNA of R. helvetica was also present in whole blood from mice, deer and wild boar. CONCLUSION:Besides R. helvetica, unexpected rickettsiae are found in I. ricinus ticks. We propose that I. ricinus is a major reservoir host for R. helvetica, and that vertebrate hosts play important roles in the further geographical dispersion of rickettsiae.

| S-EPMC2743653 | biostudies-literature

First detection of <i>Rickettsia helvetica</i> in small mammals in Lithuania.

Project description:A total of 489 small mammals belonging to seven species captured in Lithuania during 2013-2014 were investigated for Rickettsia pathogens. The overall prevalence of Rickettsia spp. was 27.6%, with a higher prevalence detected in Micromys minutus (45.9%), followed by Apodemus flavicollis (29.4%), Sorex araneus (25%) and Myodes glareolus (23.7%). Sequence analysis of the gltA gene and the 17 kDa protein coding gene revealed the presence Rickettsia helvetica. This study demonstrates not only the first reported presence of R. helvetica in small mammals in Lithuania but also the first report of R. helvetica in M. minutus more generally.

| S-EPMC5857161 | biostudies-literature

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