scholarly journals Proteolytic Cleavage of the Immunodominant Outer Membrane Protein rOmpA in Rickettsia rickettsii

2016 ◽  
Vol 199 (6) ◽  
Author(s):  
Nicholas F. Noriea ◽  
Tina R. Clark ◽  
David Mead ◽  
Ted Hackstadt
Keyword(s):  
Outer Membrane ◽  
Cleavage Site ◽  
Spotted Fever ◽  
Protein A ◽  
Rocky Mountain ◽  
Spotted Fever Group ◽  
Rocky Mountain Spotted Fever ◽  
Content Type ◽  
Rickettsia Rickettsii ◽  
Carboxy Terminal

ABSTRACT Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, contains two immunodominant proteins, rOmpA and rOmpB, in the outer membrane. Both rOmpA and rOmpB are conserved throughout spotted fever group rickettsiae as members of a family of autotransporter proteins. Previously, it was demonstrated that rOmpB is proteolytically processed, with the cleavage site residing near the autotransporter domain at the carboxy-terminal end of the protein, cleaving the 168-kDa precursor into apparent 120-kDa and 32-kDa fragments. The 120- and 32-kDa fragments remain noncovalently associated on the surface of the bacterium, with implications that the 32-kDa fragment functions as the membrane anchor domain. Here we present evidence for a similar posttranslational processing of rOmpA. rOmpA is expressed as a predicted 224-kDa precursor yet is observed on SDS-PAGE as a 190-kDa protein. A small rOmpA fragment of ∼32 kDa was discovered during surface proteome analysis and identified as the carboxy-terminal end of the protein. A rabbit polyclonal antibody was generated to the autotransporter region of rOmpA and confirmed a 32-kDa fragment corresponding to the calculated mass of a proteolytically cleaved rOmpA autotransporter region. N-terminal amino acid sequencing revealed a cleavage site on the carboxy-terminal side of Ser-1958 in rOmpA. An avirulent strain of R. rickettsii Iowa deficient in rOmpB processing was also defective in the processing of rOmpA. The similarities of the cleavage sites and the failure of R. rickettsii Iowa to process either rOmpA or rOmpB suggest that a single enzyme may be responsible for both processing events. IMPORTANCE Members of the spotted fever group of rickettsiae, including R. rickettsii, the etiologic agent of Rocky Mountain spotted fever, express at least four autotransporter proteins that are protective antigens or putative virulence determinants. One member of this class of proteins, rOmpB, is proteolytically processed to a passenger domain and an autotransporter domain that remain associated on the rickettsial outer membrane. The protease responsible for this posttranslation processing remains unknown. Here we show that another autotransporter, rOmpA, is similarly processed by R. rickettsii. Similarities in sequence at the cleavage site and predicted secondary protein structure suggest that all four R. rickettsii autotransporters may be processed by the same outer membrane protease.

scholarly journals Comparative Genome Sequencing of Rickettsia rickettsii Strains That Differ in Virulence

2015 ◽  
Vol 83 (4) ◽  
pp. 1568-1576 ◽  
Author(s):  
Tina R. Clark ◽  
Nicholas F. Noriea ◽  
DeAnna C. Bublitz ◽  
Damon W. Ellison ◽  
Craig Martens ◽  
...  
Keyword(s):  
Genome Sequencing ◽  
Surface Antigen ◽  
Tandem Repeats ◽  
Spotted Fever ◽  
Protein A ◽  
Rocky Mountain Spotted Fever ◽  
Comparative Genome ◽  
Content Type ◽  
Rickettsia Rickettsii ◽  
Major Surface

Rickettsia rickettsiiis an obligate intracellular pathogen that is the causative agent of Rocky Mountain spotted fever. Strains ofR. rickettsiidiffer dramatically in virulence. In a guinea pig model of infection, the severity of disease as assessed by fever response varies from the most virulent, Sheila Smith, to Iowa, which causes no fever. To identify potential determinants of virulence inR. rickettsii, the genomes of two additional strains were sequenced for comparison to known sequences (comparative genome sequencing [CGS]).R. rickettsiiMorgan and R strains were compared to the avirulentR. rickettsiiIowa and virulentR. rickettsiiSheila Smith strains. The Montana strains Sheila Smith and R were found to be highly similar while the eastern strains Iowa and Morgan were most similar to each other. A major surface antigen, rickettsial outer membrane protein A (rOmpA), is severely truncated in the Iowa strain. The region ofompAcontaining 13 tandem repeats was sequenced, revealing only seven shared SNPs (four nonsynonymous) for R and Morgan strains compared to Sheila Smith, with an additional 17 SNPs identified in Morgan. Another major surface antigen and autotransporter, rOmpB, exhibits a defect in processing in the Iowa strain such that the beta fragment is not cleaved. Sequence analysis ofompBreveals identical sequences between Iowa and Morgan strains and between the R and Sheila Smith strains. The number of SNPs and insertions/deletions between sequences of the two Montana strains and the two eastern strains is low, thus narrowing the field of possible virulence factors.

scholarly journals Molecular Detection of Spotted Fever Group Rickettsiae (Rickettsiales: Rickettsiaceae) in Dermacentor variabilis (Acari: Ixodidae) Collected Along the Platte River in South Central Nebraska

2019 ◽  
Vol 57 (2) ◽  
pp. 519-523
Author(s):  
Brandon E Luedtke ◽  
Julie J Shaffer ◽  
Estrella Monrroy ◽  
Corey W Willicott ◽  
Travis J Bourret
Keyword(s):  
Spotted Fever ◽  
Rocky Mountain ◽  
Dermacentor Variabilis ◽  
Amblyomma Americanum ◽  
Spotted Fever Group ◽  
Rocky Mountain Spotted Fever ◽  
Rickettsia Species ◽  
Platte River ◽  
Rickettsia Rickettsii ◽  
South Central

Abstract Dermacentor variabilis is the predominant tick species in Nebraska and is presumed to be the primary vector of Rickettsia rickettsii associated with cases of Rocky Mountain spotted fever (RMSF). Interestingly, RMSF cases in Nebraska have increased on a year-to-year basis, yet the prevalence of R. rickettsii in D. variabilis ticks has not been established for Nebraska. Here we sought to set a baseline for the prevalence of R. rickettsii and other spotted fever group (SFG) rickettsiae harbored by D. variabilis ticks. Over a 3-yr period, D. variabilis were collected along the Platte River in south central Nebraska. Individual tick DNA was analyzed using endpoint PCR to identify ticks carrying SFG rickettsiae. In total, 927 D. variabilis were analyzed by PCR and 38 (4.1%) ticks tested positive for SFG rickettsiae. Presumptive positives were sequenced to identify the Rickettsia species, of which 29 (76%) were R. montanensis, 5 (13%) were R. amblyommatis, 4 (11%) were R. bellii, and R. rickettsii was not detected. These data indicate that R. rickettsii is likely at a low prevalence in south central Nebraska and spillover of R. amblyommatis into D. variabilis is likely occurring due to the invasive lone star tick (Amblyomma americanum). In addition, our data suggest that R. montanensis and R. amblyommatis could be associated with the increase in SFG rickettsiae infections in Nebraska. This information will be of value to clinicians and the general public for evaluating diagnosis of disease- and risk-associated environmental exposure, respectively.

scholarly journals Disruption of the Rickettsia rickettsii Sca2 Autotransporter Inhibits Actin-Based Motility

2010 ◽  
Vol 78 (5) ◽  
pp. 2240-2247 ◽  
Author(s):  
Betsy Kleba ◽  
Tina R. Clark ◽  
Erika I. Lutter ◽  
Damon W. Ellison ◽  
Ted Hackstadt
Keyword(s):  
Spotted Fever ◽  
Insertion Site ◽  
Rocky Mountain ◽  
Etiologic Agent ◽  
Spotted Fever Group ◽  
Rocky Mountain Spotted Fever ◽  
Spotted Fever Group Rickettsiae ◽  
Rickettsia Rickettsii ◽  
Transposon Insertion ◽  
Guinea Pig Model

ABSTRACT Rickettsii rickettsii, the etiologic agent of Rocky Mountain spotted fever, replicates within the cytosol of infected cells and uses actin-based motility to spread inter- and intracellularly. Although the ultrastructure of the actin tail and host proteins associated with it are distinct from those of Listeria or Shigella, comparatively little is known regarding the rickettsial proteins involved in its organization. Here, we have used random transposon mutagenesis of R. rickettsii to generate a small-plaque mutant that is defective in actin-based motility and does not spread directly from cell to cell as is characteristic of spotted fever group rickettsiae. The transposon insertion site of this mutant strain was within Sca2, a member of a family of large autotransporter proteins. Sca2 exhibits several features suggestive of its apparent role in actin-based motility. It displays an N-terminal secretory signal peptide, a C-terminal predicted autotransporter domain, up to four predicted Wasp homology 2 (WH2) domains, and two proline-rich domains, one with similarity to eukaryotic formins. In a guinea pig model of infection, the Sca2 mutant did not elicit fever, suggesting that Sca2 and actin-based motility are virulence factors of spotted fever group rickettsiae.

scholarly journals Unique Strain of Rickettsia parkeri Associated with the Hard Tick Dermacentor parumapertus Neumann in the Western United States

2017 ◽  
Vol 83 (9) ◽  
Author(s):  
Christopher D. Paddock ◽  
Michelle E. J. Allerdice ◽  
Sandor E. Karpathy ◽  
William L. Nicholson ◽  
Michael L. Levin ◽  
...  
Keyword(s):  
Genetic Relatedness ◽  
Spotted Fever ◽  
Case Fatality ◽  
Rocky Mountain ◽  
Atlantic Rainforest ◽  
Spotted Fever Group ◽  
Hard Tick ◽  
Rocky Mountain Spotted Fever ◽  
Rickettsia Parkeri ◽  
Content Type

ABSTRACT In 1953, investigators at the Rocky Mountain Laboratories in Hamilton, MT, described the isolation of a spotted fever group Rickettsia (SFGR) species from Dermacentor parumapertus ticks collected from black-tailed jackrabbits (Lepus californicus) in northern Nevada. Several decades later, investigators characterized this SFGR (designated the parumapertus agent) by using mouse serotyping methods and determined that it represented a distinct rickettsial serotype closely related to Rickettsia parkeri; nonetheless, the parumapertus agent was not further characterized or studied. To our knowledge, no isolates of the parumapertus agent remain in any rickettsial culture collection, which precludes contemporary phylogenetic placement of this enigmatic SFGR. To rediscover the parumapertus agent, adult-stage D. parumapertus ticks were collected from black-tailed jackrabbits shot or encountered as roadkills in Arizona, Utah, or Texas from 2011 to 2016. A total of 339 ticks were collected and evaluated for infection with Rickettsia species. Of 112 D. parumapertus ticks collected in south Texas, 16 (14.3%) contained partial ompA sequences with the closest identity (99.6%) to Rickettsia sp. strain Atlantic rainforest Aa46, an SFGR that is closely related or identical to an SFGR species that causes a mild rickettsiosis in several states of Brazil. A pure isolate, designated strain Black Gap, was cultivated in Vero E6 cells, and sequence analysis of the rrs, gltA, sca0, sca5, and sca4 genes also revealed the closest genetic identity to Rickettsia sp. Atlantic rainforest Aa46. Phylogenetic analysis of the five concatenated rickettsial genes place Rickettsia sp. strain Black Gap and Rickettsia sp. Atlantic rainforest Aa46 with R. parkeri in a distinct and well-supported clade. IMPORTANCE We suggest that Rickettsia sp. Black Gap and Rickettsia sp. Atlantic rainforest Aa46 represent nearly identical strains of R. parkeri and that Rickettsia sp. Black Gap or a very similar strain of R. parkeri represents the parumapertus agent. The close genetic relatedness among these taxa, as well as the response of guinea pigs infected with the Black Gap strain, suggests that R. parkeri Black Gap could cause disease in humans. The identification of this organism could also account, at least in part, for the remarkable differences in severity ascribed to Rocky Mountain spotted fever (RMSF) among various regions of the American West during the early 20th century. We suggest that the wide variation in case fatality rates attributed to RMSF could have occurred by the inadvertent inclusion of cases of milder disease caused by R. parkeri Black Gap.

Rickettsial infection

2018 ◽  
Author(s):  
Tom Fletcher ◽  
Nick Beeching
Keyword(s):  
Q Fever ◽  
Spotted Fever ◽  
Rocky Mountain ◽  
Blood Feeding ◽  
Spotted Fever Group ◽  
Rocky Mountain Spotted Fever ◽  
Obligate Intracellular ◽  
Rickettsia Rickettsii ◽  
Rickettsial Infections ◽  
The Us

Rickettsial infections are caused by a variety of obligate intracellular, Gram-negative bacteria from the genera Rickettsia, Orientia, Ehrlichia, and Anaplasma. Rickettsia is further subdivided into the spotted fever group and the typhus group. Bartonella and Coxiella burnetii bacteria are similar to rickettsiae and cause similar diseases. The range of recognized spotted fever group infections is rapidly expanding, complementing long-recognized examples such as Rocky Mountain spotted fever (Rickettsia rickettsii) in the US, and Australian tick typhus (Rickettsia australis), as well as those in southern Europe and Africa. Animals are the predominant reservoir of infection, and transmission to people is usually through ticks, mites, fleas, or lice, during blood-feeding or from scarification of faeces deposited on the skin. This chapter focuses on the two of the most relevant infections encountered in UK practice: African tick typhus, and Q fever.

Spotted fever group rickettsiae in immature and adult ticks (Acari: Ixodidae) from a focus of Rocky Mountain spotted fever in Connecticut

1985 ◽  
Vol 31 (12) ◽  
pp. 1131-1135 ◽  
Author(s):  
Louis A. Magnarelli ◽  
John F. Anderson ◽  
Willy Burgdorfer ◽  
Robert N. Philip ◽  
W. Adrian Chappell
Keyword(s):  
Spotted Fever ◽  
Fluorescent Antibody ◽  
Rocky Mountain ◽  
Dermacentor Variabilis ◽  
Etiologic Agent ◽  
Ixodid Ticks ◽  
Spotted Fever Group ◽  
Rocky Mountain Spotted Fever ◽  
Serum Samples ◽  
Rickettsia Rickettsii

Immature and adult ixodid ticks were collected during 1983 and 1984 in Newtown, Connecticut, an area endemic for Rocky Mountain spotted fever (RMSF), to determine prevalence of infection by spotted fever group (SFG) rickettsiae. Direct fluorescent-antibody (FA) staining revealed SFG organisms in 6 (1.8%) of 332 Dermacentor variabilis larvae, 5 (7.8%) of 64 D. variabilis nymphs, and in 2 (40%) of 5 Ixodes cookei nymphs removed from small- and medium-sized mammals. Hemolymph tests detected rickettsia-like organisms in 15 (8.8%) of 170 D. variabilis adults; 8 specimens retested by direct FA were negative. In contrast, hemocytes from 5 (8.6%) of 58 Ixodes texanus females contained organisms that stained positively in both hemolymph and direct FA tests. An indirect microimmunofluorescence test identified specific antibodies to Rickettsia rickettsii, the etiologic agent of RMSF, in serum samples from a chipmunk, raccoons, and white-footed mice. Results indicate that immature or adult ticks of at least three species may be involved in the maintenance and transmission of SFG rickettsiae at Newtown.

Mitbringsel aus den Ferien

Praxis ◽  
2005 ◽  
Vol 94 (47) ◽  
pp. 1869-1870
Author(s):  
Balestra ◽  
Nüesch
Keyword(s):  
Rocky Mountains ◽  
Spotted Fever ◽  
Rocky Mountain ◽  
Rickettsia Conorii ◽  
Rocky Mountain Spotted Fever ◽  
Klinische Diagnose ◽  
Rickettsia Rickettsii

Eine 37-jährige Patientin stellt sich nach der Rückkehr von einer Rundreise durch Nordamerika mit einem Status febrilis seit zehn Tagen und einem makulösem extremitätenbetontem Exanthem seit einem Tag vor. Bei suggestiver Klinik und Besuch der Rocky Mountains wird ein Rocky Mountain spotted fever diagnostiziert. Die Serologie für Rickettsia conorii, die mit Rickettsia rickettsii kreuzreagiert, war positiv und bestätigte die klinische Diagnose. Allerdings konnte der beweisende vierfache Titeranstieg, möglicherweise wegen spät abgenommener ersten Serologie, nicht nachgewiesen werden. Nach zweiwöchiger antibiotischer Therapie mit Doxycycline waren Status febrilis und Exanthem regredient.

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