The Rickettsial OmpB β-Peptide of Rickettsia conorii Is Sufficient To Facilitate Factor H-Mediated Serum Resistance

ABSTRACTPathogenic species of the spotted fever groupRickettsiaare subjected to repeated exposures to the host complement system through cyclic infections of mammalian and tick hosts. The serum complement machinery is a formidable obstacle for bacteria to overcome if they endeavor to endure this endozoonotic cycle. We have previously demonstrated that that the etiologic agent of Mediterranean spotted fever,Rickettsia conorii, is susceptible to complement-mediated killing only in the presence of specific monoclonal antibodies. We have also shown that in the absence of particular neutralizing antibody,R. conoriiis resistant to the effects of serum complement. We therefore hypothesized that the interactions between fluid-phase complement regulators and conserved rickettsial outer membrane-associated proteins are critical to mediate serum resistance. We demonstrate here thatR. conoriispecifically interacts with the soluble host complement inhibitor, factor H. Depletion of factor H from normal human serum rendersR. conoriimore susceptible to C3 and membrane attack complex deposition and to complement-mediated killing. We identified the autotransporter protein rickettsial OmpB (rOmpB) as a factor H ligand and further demonstrate that the rOmpB β-peptide is sufficient to mediate resistance to the bactericidal properties of human serum. Taken together, these data reveal an additional function for the highly conserved rickettsial surface cell antigen, rOmpB, and suggest that the ability to evade complement-mediated clearance from the hematogenous circulation is a novel virulence attribute for this class of pathogens.

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Nonselective Persistence of a Rickettsia conorii Extrachromosomal Plasmid during Mammalian Infection

Infection and Immunity ◽

10.1128/iai.01205-15 ◽

2016 ◽

Vol 84 (3) ◽

pp. 790-797 ◽

Cited By ~ 12

Author(s):

Sean P. Riley ◽

Abigail I. Fish ◽

Daniel A. Garza ◽

Kaikhushroo H. Banajee ◽

Emma K. Harris ◽

...

Keyword(s):

Pathogenic Bacteria ◽

Genetic Manipulation ◽

Fluorescent Proteins ◽

Spotted Fever ◽

Rickettsia Conorii ◽

Mediterranean Spotted Fever ◽

Extrachromosomal Dna ◽

Content Type

Scientific analysis of the genusRickettsiais undergoing a rapid period of change with the emergence of viable genetic tools. The development of these tools for the mutagenesis of pathogenic bacteria will permit forward genetic analysis ofRickettsiapathogenesis. Despite these advances, uncertainty still remains regarding the use of plasmids to study these bacteria inin vivomammalian models of infection, namely, the potential for virulence changes associated with the presence of extrachromosomal DNA and nonselective persistence of plasmids in mammalian models of infection. Here, we describe the transformation ofRickettsia conoriiMalish 7 with the plasmid pRam18dRGA[AmTrCh]. TransformedR. conoriistably maintains this plasmid in infected cell cultures, expresses the encoded fluorescent proteins, and exhibits growth kinetics in cell culture similar to those of nontransformedR. conorii. Using a well-established murine model of fatal Mediterranean spotted fever, we demonstrate thatR. conorii(pRam18dRGA[AmTrCh]) elicits the same fatal outcomes in animals as its untransformed counterpart and, importantly, maintains the plasmid throughout infection in the absence of selective antibiotic pressure. Interestingly, plasmid-transformedR. conoriiwas readily observed both in endothelial cells and within circulating leukocytes. Together, our data demonstrate that the presence of an extrachromosomal DNA element in a pathogenic rickettsial species does not affect eitherin vitroproliferation orin vivoinfectivity in models of disease and that plasmids such as pRam18dRGA[AmTrCh] are valuable tools for the further genetic manipulation of pathogenic rickettsiae.

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Rickettsiosis

10.1093/med/9780199592548.003.0193 ◽

2015 ◽

Author(s):

Emmanuel A. Burdmann ◽

Vivekanad Jha

Keyword(s):

Serum Creatinine ◽

Spotted Fever ◽

Renal Involvement ◽

Adverse Outcomes ◽

Rickettsia Conorii ◽

Mediterranean Spotted Fever ◽

Spotted Fever Group ◽

Rocky Mountain Spotted Fever ◽

Murine Typhus ◽

Epidemic Typhus

Rickettsiae are obligate intracellular bacteria transmitted by arthropods to a vertebrate host. Clinically relevant rickettsioses have a similar clinical pattern, manifesting as an acute febrile disease accompanied by headache, articular and muscle pain, and malaise.Epidemic typhus is a worldwide distributed disease caused by the Rickettsia prowazekii, with a human louse as a vector. Data on epidemic typhus-related renal injury is extremely scarce.Murine typhus is caused by the Rickettsia typhi and has a rodent flea as the vector. It is one of the most frequent rickettsioses, and is usually a self-limited febrile illness. Proteinuria, haematuria, elevations in serum creatinine (SCr) and/or blood urea nitrogen (BUN) and AKI have been reported. The real frequency of renal involvement in murine typhus is unknown. Renal abnormalities recover after the infectious disease resolution.Scrub typhus, caused by the Orientia tsutsugamushi, has the Leptotrombidium mite larva as vector. It is endemic in the Tsutsugamushi triangle delimited by Japan, Australia, India, and Siberia. It can manifest either as a self-limiting disease or as a severe, life-threatening multiorgan illness. Early administration of adequate antibiotics is essential to prevent adverse outcomes. Proteinuria, haematuria, and acute kidney injury (AKI) are frequent.Tick-borne rickettsioses are caused by bacteria from the spotted fever group and have ticks as vectors. Rocky Mountain spotted fever (RMSF) is caused by Rickettsia rickettsii. It is the most severe of the spotted fever rickettsial diseases, causing significant morbidity and lethality. RMSF occurs in North, Central, and South America. Renal impairment is frequent in severe forms of RMSF. Mediterranean spotted fever is caused by Rickettsia conorii, and is endemic in the Mediterranean area. It is usually a benign disease, but may have a severe course, clinically similar to RMSF. Haematuria, proteinuria, increased serum creatinine, and AKI may occur. Japanese spotted fever is caused by Rickettsia japonica. Lethal cases are reported yearly and AKI has occurred in the context of multiple organ failure.

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Isolation of an agent of the spotted fever group rickettsia from tick eggs in Madrid, Spain

Epidemiology and Infection ◽

10.1017/s0950268800050056 ◽

1992 ◽

Vol 108 (3) ◽

pp. 555-557 ◽

Cited By ~ 4

Author(s):

C. Herrero ◽

C. Pelaz ◽

C. Martín-Bourgon

Keyword(s):

Human Serum ◽

Indirect Immunofluorescence ◽

Spotted Fever ◽

Vero Cells ◽

Rickettsia Conorii ◽

Spotted Fever Group ◽

Suitable Material ◽

Rural Villages ◽

Spotted Fever Group Rickettsia

SUMMARYTicks recovered from dogs in rural villages around Madrid (Spain) were processed to isolate rickettsiae. One sample containing mixtures of ticks and four containing eggs, in which rickettsiae had been detected by indirect immunofluorescence with a human serum highly reactive toRickettsia conorii, were decontaminated, homogenized and inoculated onto Vero cells. Two egg samples yielded a cytopathic agent that reacted positively by immunofluorescence. One sample (14H) was successfully subcultured and identified as a member of the spotted fever group rickettsia. Tick eggs provide suitable material for isolation of rickettsia.

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Mediterranean Spotted Fever: Current Knowledge and Recent Advances

Tropical Medicine and Infectious Disease ◽

10.3390/tropicalmed6040172 ◽

2021 ◽

Vol 6 (4) ◽

pp. 172

Author(s):

Nikolaos Spernovasilis ◽

Ioulia Markaki ◽

Michail Papadakis ◽

Nikolaos Mazonakis ◽

Despo Ierodiakonou

Keyword(s):

Clinical Features ◽

Current Knowledge ◽

Spotted Fever ◽

Rhipicephalus Sanguineus ◽

Molecular Techniques ◽

Rickettsia Conorii ◽

Mediterranean Spotted Fever ◽

Spotted Fever Group ◽

Serological Tests ◽

True Nature

Mediterranean spotted fever (MSF) is an emerging tick-borne rickettsiosis of the spotted fever group (SFG), endemic in the Mediterranean basin. By virtue of technological innovations in molecular genetics, it has been determined that the causative agent of MSF is Rickettsia conorii subspecies conorii. The arthropod vector of this bacterium is the brown dog tick Rhipicephalus sanguineus. The true nature of the reservoir of R. conorii conorii has not been completely deciphered yet, although many authors theorize that the canine population, other mammals, and the ticks themselves could potentially contribute as reservoirs. Typical symptoms of MSF include fever, maculopapular rash, and a characteristic eschar (“tache noire”). Atypical clinical features and severe multi-organ complications may also be present. All of these manifestations arise from the disseminated infection of the endothelium by R. conorii conorii. Several methods exist for the diagnosis of MSF. Serological tests are widely used and molecular techniques have become increasingly available. Doxycycline remains the treatment of choice, while preventive measures are focused on modification of human behavior and vector control strategies. The purpose of this review is to summarize the current knowledge on the epidemiology, pathogenesis, clinical features, diagnosis, and treatment of MSF.

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Beta Interferon-Mediated Activation of Signal Transducer and Activator of Transcription Protein 1 Interferes with Rickettsia conorii Replication in Human Endothelial Cells

Infection and Immunity ◽

10.1128/iai.05008-11 ◽

2011 ◽

Vol 79 (9) ◽

pp. 3733-3743 ◽

Cited By ~ 17

Author(s):

Punsiri M. Colonne ◽

Marina E. Eremeeva ◽

Sanjeev K. Sahni

Keyword(s):

Endothelial Cells ◽

Neutralizing Antibodies ◽

Spotted Fever ◽

Janus Kinase ◽

Rickettsia Conorii ◽

Mediterranean Spotted Fever ◽

Signal Transducer ◽

Microvascular Endothelium ◽

Content Type ◽

Beta Interferon

ABSTRACTInfection of the endothelial cell lining of blood vessels withRickettsia conorii, the causative agent of Mediterranean spotted fever, results in endothelial activation. We investigated the effects ofR. conoriiinfection on the status of the Janus kinase (JAK)-signal transducer and activator of transcription protein (STAT) signaling pathway in human microvascular endothelial cells (HMECs), the most relevant host cell type, in light of rickettsial tropism for microvascular endotheliumin vivo.R. conoriiinfection induced phosphorylation of STAT1 on tyrosine 701 and serine 727 at 24, 48, and 72 h postinfection in HMECs. Employing transcription profile analysis and neutralizing antibodies, we further determined that beta interferon (IFN-β) production and secretion are critical for STAT1 activation. Secreted IFN-β further amplified its own expression via a positive-feedback mechanism, while expression of transcription factors interferon regulatory factor 7 (IRF7) and IRF9, implicated in the IFN-β–STAT1 feedback loop, was also induced. Metabolic activity of rickettsiae was essential for the IFN-β-mediated response(s) because tetracycline treatment inhibitedR. conoriireplication, IFN-β expression, and STAT1 phosphorylation. Inclusion of IFN-β-neutralizing antibody during infection resulted in significantly enhancedR. conoriireplication, whereas addition of exogenous IFN-β had the opposite inhibitory effect. Finally, small interfering RNA-mediated knockdown further confirmed a protective role for STAT1 against intracellularR. conoriireplication. In concert, these findings implicate an important role for IFN-β-mediated STAT1 activation in innate immune responses of vascular endothelium toR. conoriiinfection.

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Prevalence of antibodies to Rickettsia conorii in human beings and dogs from Catalonia: a 20-year perspective

Epidemiology and Infection ◽

10.1017/s0950268816000261 ◽

2016 ◽

Vol 144 (9) ◽

pp. 1889-1894 ◽

Cited By ~ 7

Author(s):

E. ESPEJO ◽

M. ANDRÉS ◽

J. PÉREZ ◽

J. PRAT ◽

C. GUERRERO ◽

...

Keyword(s):

Human Serum ◽

Indirect Immunofluorescence ◽

Human Population ◽

Spotted Fever ◽

Rickettsia Conorii ◽

Mediterranean Spotted Fever ◽

Human Beings ◽

Serum Samples ◽

Human Serum Samples ◽

Nineteen 5

SUMMARYThe incidence of Mediterranean spotted fever (MSF) in Catalonia (Spain) has decreased in the last two decades. The prevalence of antibodies to Rickettsia conorii in human beings and dogs in the region of Vallès Occidental (Catalonia) was assessed by indirect immunofluorescence, and the results compared with those obtained in a similar study from 1987. Nineteen (5·0%) out of 383 human serum samples had antibodies to R. conorii. This seroprevalence was significantly lower (11·5%) (P = 0·003) than that recorded in the 1987 survey. Forty-two out (42·0%) of 100 canine serum samples had antibodies to R. conorii. A high proportion of the studied dogs (91·0%) were receiving anti-tick treatment, mainly with permethrin-imidacloprid spot-on (Advantix, Bayer, Germany). The current canine seroprevalence was not significantly different from that recorded in the 1987 survey (36.9%). In conclusion, this study shows a significant decrease in the prevalence of antibodies to R. conorii in the human population of Catalonia in the last 20 years, which corresponds with a decrease in the number of cases of MSF. We suggest that the widespread use of anti-tick treatment in dogs could limit the introduction of ticks to humans due to a reduction of infestation duration in dogs, thus contributing to the decrease in MSF incidence.

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Severe clinical forms of Mediterranean spotted fever: A case series from an endemic area in Bulgaria

Vojnosanitetski pregled ◽

10.2298/vsp160907380b ◽

2018 ◽

Vol 75 (7) ◽

pp. 704-709 ◽

Cited By ~ 1

Author(s):

Magdalena Baymakova ◽

Liliya Pekova ◽

Pavlina Parousheva ◽

Radina Andonova ◽

Kamen Plochev

Keyword(s):

Endemic Area ◽

Spotted Fever ◽

Laboratory Data ◽

Case Series ◽

Mean Value ◽

University Hospital ◽

Rickettsia Conorii ◽

Mediterranean Spotted Fever ◽

Spotted Fever Group ◽

Hepatic Disorder

Background/Aim. Mediterranean spotted fever (MSF) belongs to Rickettsioses, the Spotted fever group (SFG). The causal agent is Rickettsia conorii conorii and the transmission to humans occurs through dog tick Rhipicephalus sanguineus bites. The aim of this study was to describe clinical and laboratory characteristics in patients with severe form of Mediterranean spotted fever admitted to Bulgarian university hospital in endemic region. Methods. A retrospective study was conducted at Stara Zagora University Hospital (Southeastern Bulgaria) between April 2015 and August 2016. During the analyzed period, 58 cases had clinical and laboratory data for MSF. Serological tests were applied for the etiological diagnosis. MSF-specific immunoglobulin (IgM) and IgG antibodies were detected in serum by indirect immunoenzyme assay (ELISA IgG/IgM, Vircell, Spain) ? R. conorii ELISA IgG sensitivity 85%, specificity 100% and R. conorii ELISA IgM sensitivity 94%, specificity 95%. Statistical analysis was made by MS Excel 2007 and SPSS Statistics, version 19.0. Results. Eighteen patients presented as severe forms. The predominant gender of them were males (78%) and 22% were females. The median age of the analyzed group was 55 years (range: 14? 78 years). Ten patients developed hepatic disorder while 4 had neurological signs. Laboratory data showed thrombocytopenia in 15 patients, mean value of platelet (PLT) count for the whole group was 108.6 ? 53.8 ? 109/L. Liver enzymes were elevated with mean value of aspartate aminotransferase (AST) 161.4 ? 90.1 IU/L and alanine aminotransferase (ALT) 163.9 ? 81.5 IU/L. Acute phase reactant as C-reactive protein (CRP) had mean value of 140.3 mg/L (range: 9?230 mg/L). Kidney function was impaired in some cases; the mean value of creatinine for the studied group was 134.7 ?mol/L (range: 78?313 ?mol/L) and mean value of urea was 9.6 mmol/L (range: 4.2?27.4 mmol/L). Conclusion. Bulgaria is an endemic area for tick-borne diseases. Cases of MSF are reported annually. Severe forms of MSF are not rare. Typical clinical and laboratory markers for severity should be actively searched for. Early diagnosis and proper treatment is the key to avoid complications and enable patient recovery.

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MyD88 Mediates Instructive Signaling in Dendritic Cells and Protective Inflammatory Response during Rickettsial Infection

Infection and Immunity ◽

10.1128/iai.01361-15 ◽

2016 ◽

Vol 84 (4) ◽

pp. 883-893 ◽

Cited By ~ 12

Author(s):

Jeremy Bechelli ◽

Claire Smalley ◽

Xuemei Zhao ◽

Barbara Judy ◽

Patricia Valdes ◽

...

Keyword(s):

Dendritic Cells ◽

Inflammatory Response ◽

Spotted Fever ◽

Host Susceptibility ◽

Rickettsia Conorii ◽

Spotted Fever Group ◽

Rickettsial Infection ◽

Content Type ◽

Ifn Γ

Spotted fever group rickettsiae cause potentially life-threatening infections throughout the world. Several members of the Toll-like receptor (TLR) family are involved in host response to rickettsiae, and yet the mechanisms by which these TLRs mediate host immunity remain incompletely understood. In the present study, we found that host susceptibility of MyD88−/−mice to infection withRickettsia conoriiorRickettsia australiswas significantly greater than in wild-type (WT) mice, in association with severely impaired bacterial clearancein vivo.R. australis-infected MyD88−/−mice showed significantly lower expression levels of gamma interferon (IFN-γ), interleukin-6 (IL-6), and IL-1β, accompanied by significantly fewer inflammatory infiltrates of macrophages and neutrophils in infected tissues, than WT mice. The serum levels of IFN-γ, IL-12, IL-6, and granulocyte colony-stimulating factor were significantly reduced, while monocyte chemoattractant protein 1, macrophage inflammatory protein 1α, and RANTES were significantly increased in infected MyD88−/−mice compared to WT mice. Strikingly,R. australisinfection was incapable of promoting increased expression of MHC-IIhighand production of IL-12p40 in MyD88−/−bone marrow-derived dendritic cells (BMDCs) compared to WT BMDCs, although costimulatory molecules were upregulated in both types of BMDCs. Furthermore, the secretion levels of IL-1β byRickettsia-infected BMDCs and in the sera of infected mice were significantly reduced in MyD88−/−mice compared to WT controls, suggesting thatin vitroandin vivoproduction of IL-1β is MyD88 dependent. Taken together, our results suggest that MyD88 signaling mediates instructive signals in DCs and secretion of IL-1β and type 1 immune cytokines, which may account for the protective inflammatory response during rickettsial infection.

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Significant Growth by Rickettsia Species within Human Macrophage-Like Cells Is a Phenotype Correlated with the Ability to Cause Disease in Mammals

Pathogens ◽

10.3390/pathogens10020228 ◽

2021 ◽

Vol 10 (2) ◽

pp. 228

Author(s):

M. Nathan Kristof ◽

Paige E. Allen ◽

Lane D. Yutzy ◽

Brandon Thibodaux ◽

Christopher D. Paddock ◽

...

Keyword(s):

Endothelial Cells ◽

Spotted Fever ◽

Growth Characteristic ◽

Human Macrophage ◽

Rickettsia Conorii ◽

Spotted Fever Group ◽

Rocky Mountain Spotted Fever ◽

Phagocytic Cells ◽

Pathogenic Potential ◽

Rickettsia Species

Rickettsia are significant sources of tick-borne diseases in humans worldwide. In North America, two species in the spotted fever group of Rickettsia have been conclusively associated with disease of humans: Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, and Rickettsia parkeri, the cause of R. parkeri rickettsiosis. Previous work in our lab demonstrated non-endothelial parasitism by another pathogenic SFG Rickettsia species, Rickettsia conorii, within THP-1-derived macrophages, and we have hypothesized that this growth characteristic may be an underappreciated aspect of rickettsial pathogenesis in mammalian hosts. In this work, we demonstrated that multiple other recognized human pathogenic species of Rickettsia, including R. rickettsii, R. parkeri, Rickettsia africae, and Rickettsiaakari can grow within target endothelial cells as well as within PMA-differentiated THP-1 cells. In contrast, Rickettsia bellii, a Rickettsia species not associated with disease of humans, and R. rickettsii strain Iowa, an avirulent derivative of pathogenic R. rickettsii, could invade both cell types but proliferate only within endothelial cells. Further analysis revealed that similar to previous studies on R. conorii, other recognized pathogenic Rickettsia species could grow within the cytosol of THP-1-derived macrophages and avoided localization with two different markers of lysosomal compartments; LAMP-2 and cathepsin D. R. bellii, on the other hand, demonstrated significant co-localization with lysosomal compartments. Collectively, these findings suggest that the ability of pathogenic rickettsial species to establish a niche within macrophage-like cells could be an important factor in their ability to cause disease in mammals. These findings also suggest that analysis of growth within mammalian phagocytic cells may be useful to predict the pathogenic potential of newly isolated and identified Rickettsia species.

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