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Abdu F. Azad - One of the best experts on this subject based on the ideXlab platform.
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Risk1, a Phosphatidylinositol 3-Kinase Effector, Promotes Rickettsia typhi Intracellular Survival
mBio, 2020Co-Authors: Oliver H. Voss, M. Sayeedur Rahman, Joseph J Gillespie, Stephanie S. Lehman, Sherri A. Rennoll, Magda Beier-sexton, Abdu F. AzadAbstract:ABSTRACT To establish a habitable intracellular niche, various pathogenic bacteria secrete effectors that target intracellular trafficking and modulate phosphoinositide (PI) metabolism. Murine typhus, caused by the obligate intracellular bacterium Rickettsia typhi, remains a severe disease in humans. However, the mechanisms by which R. typhi effector molecules contribute to internalization by induced phagocytosis and subsequent phagosomal escape into the cytosol to facilitate the intracellular growth of the bacteria remain ill-defined. Here, we characterize a new molecule, Risk1, as a phosphatidylinositol 3-kinase (PI3K) secreted effector and the first bacterial secretory kinase with both class I and III PI3K activities. Inactivation of Risk1 PI3K activities reduced the phosphorylation of phosphatidylinositol 4,5-bisphosphate to phosphatidylinositol 3,4,5-trisphosphate within the host, which consequently diminished host colonization by R. typhi. During infection, Risk1 targets the Rab5-EEA1-phosphatidylinositol 3-phosphate [PI(3)P] signaling axis to promote bacterial phagosomal escape. Subsequently, R. typhi undergoes ubiquitination and induces host autophagy; however, maturation to autolysosomes is subverted to support intracellular growth. Intriguingly, only enzymatically active Risk1 binds the Beclin-1 core complex and contributes to R. typhi-induced autophagosome formation. In sum, our data suggest that Risk1, with dual class I and class III PI3K activities, alters host PI metabolism and consequently subverts intracellular trafficking to facilitate intracellular growth of R. typhi. IMPORTANCERickettsia species are Gram-negative obligate intracellular bacteria that infect a wide range of eukaryotes and vertebrates. In particular, human body louse-borne Rickettsia prowazekii and flea-borne Rickettsia typhi have historically plagued humankind and continue to reemerge globally. The unavailability of vaccines and limited effectiveness of antibiotics late in infection place lethality rates up to 30%, highlighting the need to elucidate the mechanisms of Rickettsia pathogenicity in greater detail. Here, we characterize a new effector, Risk1, as a secreted phosphatidylinositol 3-kinase (PI3K) with unique dual class I and class III activities. Risk1 is required for host colonization, and its vacuolar phosphatidylinositol 3-phosphate generation modulates endosomal trafficking to arrest autophagosomal maturation. Collectively, Risk1 facilitates R. typhi growth by altering phosphoinositide metabolism and subverting intracellular trafficking.
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the cat flea ctenocephalides felis immune deficiency signaling pathway regulates Rickettsia typhi infection
Infection and Immunity, 2017Co-Authors: Sherri A. Rennoll, Sayeedur M Rahman, Magda Beiersexton, Joseph J Gillespie, Stephanie S. Lehman, Kristen E Rennollbankert, Mark L Guillotte, Timothy Driscoll, Abdu F. AzadAbstract:Rickettsia species are obligate intracellular bacteria with both conserved and lineage-specific strategies for invading and surviving within eukaryotic cells. One variable component of Rickettsia biology involves arthropod vectors: for instance, typhus group Rickettsiae are principally vectored by insects (i.e., lice and fleas), whereas spotted fever group Rickettsiae are exclusively vectored by ticks. For flea-borne Rickettsia typhi, the etiological agent of murine typhus, research on vertebrate host biology is facilitated using cell lines and animal models. However, due to the lack of any stable flea cell line or a published flea genome sequence, little is known regarding R. typhi biology in flea vectors that, importantly, do not suffer lethality due to R. typhi infection. To address if fleas combat Rickettsial infection, we characterized the cat flea (Ctenocephalides felis) innate immune response to R. typhi Initially, we determined that R. typhi infects Drosophila cells and increases antimicrobial peptide (AMP) gene expression, indicating immune pathway activation. While bioinformatics analysis of the C. felis transcriptome identified homologs to all of the Drosophila immune deficiency (IMD) and Toll pathway components, an AMP gene expression profile in Drosophila cells indicated IMD pathway activation upon Rickettsial infection. Accordingly, we assessed R. typhi-mediated flea IMD pathway activation in vivo using small interfering RNA (siRNA)-mediated knockdown. Knockdown of Relish and Imd increased R. typhi infection levels, implicating the IMD pathway as a critical regulator of R. typhi burden in C. felis These data suggest that targeting the IMD pathway could minimize the spread of R. typhi, and potentially other human pathogens, vectored by fleas.
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RalF-Mediated Activation of Arf6 Controls Rickettsia typhi Invasion by Co-Opting Phosphoinositol Metabolism.
Infection and immunity, 2016Co-Authors: Kristen E. Rennoll-bankert, M. Sayeedur Rahman, Joseph J Gillespie, Stephanie S. Lehman, Magda Beier-sexton, Mark L Guillotte, Abdu F. AzadAbstract:Rickettsiae are obligate intracellular pathogens that induce their uptake into nonphagocytic cells; however, the events instigating this process are incompletely understood. Importantly, diverse Rickettsia species are predicted to utilize divergent mechanisms to colonize host cells, as nearly all adhesins and effectors involved in host cell entry are differentially encoded in diverse Rickettsia species. One particular effector, RalF, a Sec7 domain-containing protein that functions as a guanine nucleotide exchange factor of ADP-ribosylation factors (Arfs), is critical for Rickettsia typhi (typhus group Rickettsiae) entry but pseudogenized or absent from spotted fever group Rickettsiae. Secreted early during R. typhi infection, RalF localizes to the host plasma membrane and interacts with host ADP-ribosylation factor 6 (Arf6). Herein, we demonstrate that RalF activates Arf6, a process reliant on a conserved Glu within the RalF Sec7 domain. Furthermore, Arf6 is activated early during infection, with GTP-bound Arf6 localized to the R. typhi entry foci. The regulation of phosphatidylinositol 4-phosphate 5-kinase (PIP5K), which generates PI(4,5)P2, by activated Arf6 is instrumental for bacterial entry, corresponding to the requirement of PI(4,5)P2 for R. typhi entry. PI(3,4,5)P3 is then synthesized at the entry foci, followed by the accumulation of PI(3)P on the short-lived vacuole. Inhibition of phosphoinositide 3-kinases, responsible for the synthesis of PI(3,4,5)P3 and PI(3)P, negatively affects R. typhi infection. Collectively, these results identify RalF as the first bacterial effector to directly activate Arf6, a process that initiates alterations in phosphoinositol metabolism critical for a lineage-specific Rickettsia entry mechanism.
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tolc dependent secretion of an ankyrin repeat containing protein of Rickettsia typhi
Journal of Bacteriology, 2012Co-Authors: Simran J Kaur, Shane M Ceraul, Sayeedur M Rahman, Nicole C Ammerman, Magda Beiersexton, Joseph J Gillespie, Abdu F. AzadAbstract:Rickettsia typhi, the causative agent of murine (endemic) typhus, is an obligate intracellular pathogen with a life cycle involving both vertebrate and invertebrate hosts. In this study, we characterized a gene (RT0218) encoding a C-terminal ankyrin repeat domain-containing protein, named Rickettsia ankyrin repeat protein 1 (RARP-1), and identified it as a secreted effector protein of R. typhi. RT0218 showed differential transcript abundance at various phases of R. typhi intracellular growth. RARP-1 was secreted by R. typhi into the host cytoplasm during in vitro infection of mammalian cells. Transcriptional analysis revealed that RT0218 was cotranscribed with adjacent genes RT0217 (hypothetical protein) and RT0216 (TolC) as a single polycistronic mRNA. Given one of its functions as a facilitator of extracellular protein secretion in some Gram-negative bacterial pathogens, we tested the possible role of TolC in the secretion of RARP-1. Using Escherichia coli C600 and an isogenic tolC insertion mutant as surrogate hosts, our data demonstrate that RARP-1 is secreted in a TolC-dependent manner. Deletion of either the N-terminal signal peptide or the C-terminal ankyrin repeats abolished RARP-1 secretion by wild-type E. coli. Importantly, expression of R. typhi tolC in the E. coli tolC mutant restored the secretion of RARP-1, suggesting that TolC has a role in RARP-1 translocation across the outer membrane. This work implies that the TolC component of the putative type 1 secretion system of R. typhi is involved in the secretion process of RARP-1.
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Functional Characterization of a Phospholipase A2 Homolog from Rickettsia typhi
Journal of bacteriology, 2010Co-Authors: M. Sayeedur Rahman, Shane M Ceraul, Nicole C Ammerman, Khandra T. Sears, Abdu F. AzadAbstract:Phospholipase A2 (PLA2) has long been proposed to be involved in Rickettsial entry into host cells, escape from the phagosome to evade destruction by lysosomal exposure, and lysis of the host cells. However, the corresponding Rickettsial gene(s) encoding a protein with PLA2 activity has not been identified or functionally characterized. Here, we report that the Rickettsia typhi genome possesses two genes encoding patatin-like PLA2 proteins, RT0590 and RT0522. Sequence analysis of RT0522 and RT0590 reveals the presence of the conserved motifs essential for PLA2 activity. Transcriptional analysis indicates that RT0522, but not RT0590, is transcribed at all stages of intracellular growth of R. typhi in Vero cells. The differential gene expression pattern of RT0522 at various stages of growth suggests its potential role during R. typhi infection of host cells. In silico, RT0522 is predicted to be noncytoplasmic and its gene does not encode a recognizable signal peptide sequence. However, our data indicate that RT0522 is secreted into the host cytoplasm. In addition, we observe that RT0522 protein expression is cytotoxic to both yeast and Vero cells. Importantly, we demonstrate that recombinant RT0522 possesses phospholipase A activity that requires a eukaryotic host cofactor for activation. Both cytotoxicity and phospholipase A activity associated with RT0522 were reduced by PLA2 inhibitors. Site-directed mutagenesis of predicted catalytic Ser/Asp residues of RT0522 also eliminates cytotoxicity and phospholipase A activity. To our knowledge, RT0522 is the first protein identified from Rickettsia typhi with functional phospholipase A activity.
M. Sayeedur Rahman - One of the best experts on this subject based on the ideXlab platform.
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Risk1, a Phosphatidylinositol 3-Kinase Effector, Promotes Rickettsia typhi Intracellular Survival
mBio, 2020Co-Authors: Oliver H. Voss, M. Sayeedur Rahman, Joseph J Gillespie, Stephanie S. Lehman, Sherri A. Rennoll, Magda Beier-sexton, Abdu F. AzadAbstract:ABSTRACT To establish a habitable intracellular niche, various pathogenic bacteria secrete effectors that target intracellular trafficking and modulate phosphoinositide (PI) metabolism. Murine typhus, caused by the obligate intracellular bacterium Rickettsia typhi, remains a severe disease in humans. However, the mechanisms by which R. typhi effector molecules contribute to internalization by induced phagocytosis and subsequent phagosomal escape into the cytosol to facilitate the intracellular growth of the bacteria remain ill-defined. Here, we characterize a new molecule, Risk1, as a phosphatidylinositol 3-kinase (PI3K) secreted effector and the first bacterial secretory kinase with both class I and III PI3K activities. Inactivation of Risk1 PI3K activities reduced the phosphorylation of phosphatidylinositol 4,5-bisphosphate to phosphatidylinositol 3,4,5-trisphosphate within the host, which consequently diminished host colonization by R. typhi. During infection, Risk1 targets the Rab5-EEA1-phosphatidylinositol 3-phosphate [PI(3)P] signaling axis to promote bacterial phagosomal escape. Subsequently, R. typhi undergoes ubiquitination and induces host autophagy; however, maturation to autolysosomes is subverted to support intracellular growth. Intriguingly, only enzymatically active Risk1 binds the Beclin-1 core complex and contributes to R. typhi-induced autophagosome formation. In sum, our data suggest that Risk1, with dual class I and class III PI3K activities, alters host PI metabolism and consequently subverts intracellular trafficking to facilitate intracellular growth of R. typhi. IMPORTANCERickettsia species are Gram-negative obligate intracellular bacteria that infect a wide range of eukaryotes and vertebrates. In particular, human body louse-borne Rickettsia prowazekii and flea-borne Rickettsia typhi have historically plagued humankind and continue to reemerge globally. The unavailability of vaccines and limited effectiveness of antibiotics late in infection place lethality rates up to 30%, highlighting the need to elucidate the mechanisms of Rickettsia pathogenicity in greater detail. Here, we characterize a new effector, Risk1, as a secreted phosphatidylinositol 3-kinase (PI3K) with unique dual class I and class III activities. Risk1 is required for host colonization, and its vacuolar phosphatidylinositol 3-phosphate generation modulates endosomal trafficking to arrest autophagosomal maturation. Collectively, Risk1 facilitates R. typhi growth by altering phosphoinositide metabolism and subverting intracellular trafficking.
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RalF-Mediated Activation of Arf6 Controls Rickettsia typhi Invasion by Co-Opting Phosphoinositol Metabolism.
Infection and immunity, 2016Co-Authors: Kristen E. Rennoll-bankert, M. Sayeedur Rahman, Joseph J Gillespie, Stephanie S. Lehman, Magda Beier-sexton, Mark L Guillotte, Abdu F. AzadAbstract:Rickettsiae are obligate intracellular pathogens that induce their uptake into nonphagocytic cells; however, the events instigating this process are incompletely understood. Importantly, diverse Rickettsia species are predicted to utilize divergent mechanisms to colonize host cells, as nearly all adhesins and effectors involved in host cell entry are differentially encoded in diverse Rickettsia species. One particular effector, RalF, a Sec7 domain-containing protein that functions as a guanine nucleotide exchange factor of ADP-ribosylation factors (Arfs), is critical for Rickettsia typhi (typhus group Rickettsiae) entry but pseudogenized or absent from spotted fever group Rickettsiae. Secreted early during R. typhi infection, RalF localizes to the host plasma membrane and interacts with host ADP-ribosylation factor 6 (Arf6). Herein, we demonstrate that RalF activates Arf6, a process reliant on a conserved Glu within the RalF Sec7 domain. Furthermore, Arf6 is activated early during infection, with GTP-bound Arf6 localized to the R. typhi entry foci. The regulation of phosphatidylinositol 4-phosphate 5-kinase (PIP5K), which generates PI(4,5)P2, by activated Arf6 is instrumental for bacterial entry, corresponding to the requirement of PI(4,5)P2 for R. typhi entry. PI(3,4,5)P3 is then synthesized at the entry foci, followed by the accumulation of PI(3)P on the short-lived vacuole. Inhibition of phosphoinositide 3-kinases, responsible for the synthesis of PI(3,4,5)P3 and PI(3)P, negatively affects R. typhi infection. Collectively, these results identify RalF as the first bacterial effector to directly activate Arf6, a process that initiates alterations in phosphoinositol metabolism critical for a lineage-specific Rickettsia entry mechanism.
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Functional Characterization of a Phospholipase A2 Homolog from Rickettsia typhi
Journal of bacteriology, 2010Co-Authors: M. Sayeedur Rahman, Shane M Ceraul, Nicole C Ammerman, Khandra T. Sears, Abdu F. AzadAbstract:Phospholipase A2 (PLA2) has long been proposed to be involved in Rickettsial entry into host cells, escape from the phagosome to evade destruction by lysosomal exposure, and lysis of the host cells. However, the corresponding Rickettsial gene(s) encoding a protein with PLA2 activity has not been identified or functionally characterized. Here, we report that the Rickettsia typhi genome possesses two genes encoding patatin-like PLA2 proteins, RT0590 and RT0522. Sequence analysis of RT0522 and RT0590 reveals the presence of the conserved motifs essential for PLA2 activity. Transcriptional analysis indicates that RT0522, but not RT0590, is transcribed at all stages of intracellular growth of R. typhi in Vero cells. The differential gene expression pattern of RT0522 at various stages of growth suggests its potential role during R. typhi infection of host cells. In silico, RT0522 is predicted to be noncytoplasmic and its gene does not encode a recognizable signal peptide sequence. However, our data indicate that RT0522 is secreted into the host cytoplasm. In addition, we observe that RT0522 protein expression is cytotoxic to both yeast and Vero cells. Importantly, we demonstrate that recombinant RT0522 possesses phospholipase A activity that requires a eukaryotic host cofactor for activation. Both cytotoxicity and phospholipase A activity associated with RT0522 were reduced by PLA2 inhibitors. Site-directed mutagenesis of predicted catalytic Ser/Asp residues of RT0522 also eliminates cytotoxicity and phospholipase A activity. To our knowledge, RT0522 is the first protein identified from Rickettsia typhi with functional phospholipase A activity.
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Characterization of Sec-Translocon-Dependent Extracytoplasmic Proteins of Rickettsia typhi
Journal of bacteriology, 2008Co-Authors: Nicole C Ammerman, M. Sayeedur Rahman, Abdu F. AzadAbstract:As obligate intracellular, vector-borne bacteria, Rickettsiae must adapt to both mammalian and arthropod host cell environments. Deciphering the molecular mechanisms of the interactions between Rickettsiae and their host cells has largely been hindered by the genetic intractability of these organisms; however, research in other gram-negative pathogens has demonstrated that many bacterial determinants of attachment, entry, and pathogenesis are extracytoplasmic proteins. The annotations of several Rickettsial genomes indicate the presence of homologs of the Sec translocon, the major route for bacterial protein secretion from the cytoplasm. For Rickettsia typhi, the etiologic agent of murine typhus, homologs of the Sec-translocon-associated proteins LepB, SecA, and LspA have been functionally characterized; therefore, the R. typhi Sec apparatus represents a mechanism for the secretion of Rickettsial proteins, including virulence factors, into the extracytoplasmic environment. Our objective was to characterize such Sec-dependent R. typhi proteins in the context of a mammalian host cell infection. By using the web-based programs LipoP, SignalP, and Phobius, a total of 191 R. typhi proteins were predicted to contain signal peptides targeting them to the Sec translocon. Of these putative signal peptides, 102 were tested in an Escherichia coli-based alkaline phosphatase (PhoA) gene fusion system. Eighty-four of these candidates exhibited signal peptide activity in E. coli, and transcriptional analysis indicated that at least 54 of the R. typhi extracytoplasmic proteins undergo active gene expression during infections of HeLa cells. This work highlights a number of interesting proteins possibly involved in Rickettsial growth and virulence in mammalian cells.
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Genome-wide screen for temperature-regulated genes of the obligate intracellular bacterium, Rickettsia typhi
BMC Microbiology, 2008Co-Authors: Sheila M Dreher-lesnick, Shane M Ceraul, M. Sayeedur Rahman, Abdu F. AzadAbstract:Background The ability of Rickettsiae to survive in multiple eukaryotic host environments provides a good model for studying pathogen-host molecular interactions. Rickettsia typhi , the etiologic agent of murine typhus, is a strictly intracellular gram negative α-proteobacterium, which is transmitted to humans by its arthropod vector, the oriental rat flea, Xenopsylla cheopis . Thus, R. typhi must cycle between mammalian and flea hosts, two drastically different environments. We hypothesize that temperature plays a role in regulating host-specific gene expression, allowing R. typhi to survive in mammalian and arthropod hosts. In this study, we used Affymetrix microarrays to screen for temperature-induced genes upon a temperature shift from 37°C to 25°C, mimicking the two different host temperatures in vitro . Results Temperature-responsive genes belonged to multiple functional categories including among others, transcription, translation, posttranslational modification/protein turnover/chaperones and intracellular trafficking and secretion. A large number of differentially expressed genes are still poorly characterized, and either have no known function or are not in the COG database. The microarray results were validated with quantitative real time RT-PCR. Conclusion This microarray screen identified various genes that were differentially expressed upon a shift in temperature from 37°C to 25°C. Further characterization of the identified genes may provide new insights into the ability of R. typhi to successfully transition between its mammalian and arthropod hosts.
Shane M Ceraul - One of the best experts on this subject based on the ideXlab platform.
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tolc dependent secretion of an ankyrin repeat containing protein of Rickettsia typhi
Journal of Bacteriology, 2012Co-Authors: Simran J Kaur, Shane M Ceraul, Sayeedur M Rahman, Nicole C Ammerman, Magda Beiersexton, Joseph J Gillespie, Abdu F. AzadAbstract:Rickettsia typhi, the causative agent of murine (endemic) typhus, is an obligate intracellular pathogen with a life cycle involving both vertebrate and invertebrate hosts. In this study, we characterized a gene (RT0218) encoding a C-terminal ankyrin repeat domain-containing protein, named Rickettsia ankyrin repeat protein 1 (RARP-1), and identified it as a secreted effector protein of R. typhi. RT0218 showed differential transcript abundance at various phases of R. typhi intracellular growth. RARP-1 was secreted by R. typhi into the host cytoplasm during in vitro infection of mammalian cells. Transcriptional analysis revealed that RT0218 was cotranscribed with adjacent genes RT0217 (hypothetical protein) and RT0216 (TolC) as a single polycistronic mRNA. Given one of its functions as a facilitator of extracellular protein secretion in some Gram-negative bacterial pathogens, we tested the possible role of TolC in the secretion of RARP-1. Using Escherichia coli C600 and an isogenic tolC insertion mutant as surrogate hosts, our data demonstrate that RARP-1 is secreted in a TolC-dependent manner. Deletion of either the N-terminal signal peptide or the C-terminal ankyrin repeats abolished RARP-1 secretion by wild-type E. coli. Importantly, expression of R. typhi tolC in the E. coli tolC mutant restored the secretion of RARP-1, suggesting that TolC has a role in RARP-1 translocation across the outer membrane. This work implies that the TolC component of the putative type 1 secretion system of R. typhi is involved in the secretion process of RARP-1.
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Functional Characterization of a Phospholipase A2 Homolog from Rickettsia typhi
Journal of bacteriology, 2010Co-Authors: M. Sayeedur Rahman, Shane M Ceraul, Nicole C Ammerman, Khandra T. Sears, Abdu F. AzadAbstract:Phospholipase A2 (PLA2) has long been proposed to be involved in Rickettsial entry into host cells, escape from the phagosome to evade destruction by lysosomal exposure, and lysis of the host cells. However, the corresponding Rickettsial gene(s) encoding a protein with PLA2 activity has not been identified or functionally characterized. Here, we report that the Rickettsia typhi genome possesses two genes encoding patatin-like PLA2 proteins, RT0590 and RT0522. Sequence analysis of RT0522 and RT0590 reveals the presence of the conserved motifs essential for PLA2 activity. Transcriptional analysis indicates that RT0522, but not RT0590, is transcribed at all stages of intracellular growth of R. typhi in Vero cells. The differential gene expression pattern of RT0522 at various stages of growth suggests its potential role during R. typhi infection of host cells. In silico, RT0522 is predicted to be noncytoplasmic and its gene does not encode a recognizable signal peptide sequence. However, our data indicate that RT0522 is secreted into the host cytoplasm. In addition, we observe that RT0522 protein expression is cytotoxic to both yeast and Vero cells. Importantly, we demonstrate that recombinant RT0522 possesses phospholipase A activity that requires a eukaryotic host cofactor for activation. Both cytotoxicity and phospholipase A activity associated with RT0522 were reduced by PLA2 inhibitors. Site-directed mutagenesis of predicted catalytic Ser/Asp residues of RT0522 also eliminates cytotoxicity and phospholipase A activity. To our knowledge, RT0522 is the first protein identified from Rickettsia typhi with functional phospholipase A activity.
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genome wide screen for temperature regulated genes of the obligate intracellular bacterium Rickettsia typhi
BMC Microbiology, 2008Co-Authors: Sheila M Dreherlesnick, Shane M Ceraul, Sayeedur M Rahman, Abdu F. AzadAbstract:Background The ability of Rickettsiae to survive in multiple eukaryotic host environments provides a good model for studying pathogen-host molecular interactions. Rickettsia typhi, the etiologic agent of murine typhus, is a strictly intracellular gram negative α-proteobacterium, which is transmitted to humans by its arthropod vector, the oriental rat flea, Xenopsylla cheopis. Thus, R. typhi must cycle between mammalian and flea hosts, two drastically different environments. We hypothesize that temperature plays a role in regulating host-specific gene expression, allowing R. typhi to survive in mammalian and arthropod hosts. In this study, we used Affymetrix microarrays to screen for temperature-induced genes upon a temperature shift from 37°C to 25°C, mimicking the two different host temperatures in vitro.
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Genome-wide screen for temperature-regulated genes of the obligate intracellular bacterium, Rickettsia typhi
BMC Microbiology, 2008Co-Authors: Sheila M Dreher-lesnick, Shane M Ceraul, M. Sayeedur Rahman, Abdu F. AzadAbstract:Background The ability of Rickettsiae to survive in multiple eukaryotic host environments provides a good model for studying pathogen-host molecular interactions. Rickettsia typhi , the etiologic agent of murine typhus, is a strictly intracellular gram negative α-proteobacterium, which is transmitted to humans by its arthropod vector, the oriental rat flea, Xenopsylla cheopis . Thus, R. typhi must cycle between mammalian and flea hosts, two drastically different environments. We hypothesize that temperature plays a role in regulating host-specific gene expression, allowing R. typhi to survive in mammalian and arthropod hosts. In this study, we used Affymetrix microarrays to screen for temperature-induced genes upon a temperature shift from 37°C to 25°C, mimicking the two different host temperatures in vitro . Results Temperature-responsive genes belonged to multiple functional categories including among others, transcription, translation, posttranslational modification/protein turnover/chaperones and intracellular trafficking and secretion. A large number of differentially expressed genes are still poorly characterized, and either have no known function or are not in the COG database. The microarray results were validated with quantitative real time RT-PCR. Conclusion This microarray screen identified various genes that were differentially expressed upon a shift in temperature from 37°C to 25°C. Further characterization of the identified genes may provide new insights into the ability of R. typhi to successfully transition between its mammalian and arthropod hosts.
Didier Raoult - One of the best experts on this subject based on the ideXlab platform.
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RATS, FLEAS AND PUBLIC HEALTH IN KISANGANI High Prevalence of Rickettsia typhi and Bartonella Species in Rats and Fleas, Kisangani, Democratic Republic of the Congo
2014Co-Authors: Anne Laudisoit, Philippe Parola, Dadi Falay, Nicaise Amundala, Dudu Akaibe, Joëlle Goüy De Bellocq, Matteo Breno, Erik Verheyen, Liesbeth I. Wilschut, Didier RaoultAbstract:The prevalence and identity of Rickettsia and Bartonella in urban rat and flea populations were evaluated in Kisangani, Democratic Republic of the Congo (DRC) by molecular tools. An overall prevalence of 17% Bartonella species and 13% Rickettsia typhi, the agent of murine typhus, was found in the cosmopolitan rat species, Rattus rattus and Rattus norvegicus that were infested by a majority of Xenopsylla cheopis fleas. Bartonella queenslandensis, Bartonella elizabethae, and three Bartonella genotypes were identified by sequencing in rat specimens, mostly in R. rattus. Rickettsia typhi was detected in 72% of X. cheopis pools, the main vector and reservoir of this zoonotic pathogen. Co-infections were observed in rodents, suggesting a common mammalian host shared by R. typhi and Bartonella spp. Thus, both infections are endemic in DRC and the medical staffs need to be aware knowing the high prevalence of impoverished populations or immunocompromised inhabitants in this area.
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Molecular detection of Rickettsia typhi and Rickettsia felis in fleas from Algeria.
Clinical Microbiology and Infection, 2009Co-Authors: Idir Bitam, B Baziz, Tahar Kernif, Philippe Parola, Zoubir Harrat, Didier RaoultAbstract:With the exception of the rat flea Xenopsylla cheopis and Yersinia pestis, the agent of plague, fleas and human flea-borne infections have been scarcely studied in Algeria [1]. Murine typhus, a typhus group rickettsiosis caused by Rickettsia typhi and transmitted by X. cheopis, is also known to occur in Algeria, but cases are poorly documented [2,3]. However, recently, fleas collected in Algeria, in the district of Oran, between July and September 2003 (Ctenocephalides canis from rodents, and Archeopsylla erinacei from hedgehogs) were tested by PCR for the presence of Rickettsia spp., and were shown to harbour an emerging pathogen, Rickettsia felis [4]. In this work, in an effort to identify the possible aetiological agents and vectors for rickettsiosis affecting humans in Algeria, we analysed more fleas collected from rodents trapped in peridomestic areas for evidence of Rickettsial infection.
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Molecular detection of Rickettsia felis, Rickettsia typhi and two genotypes closely related to Bartonella elizabethae.
The American journal of tropical medicine and hygiene, 2006Co-Authors: Rita De Sousa, Pierre Edouard-fournier, M.m. Santos-silva, Fátima Amaro, Fátima Bacellar, Didier RaoultAbstract:A total of 56 fleas were collected from mice, rats, and one hedgehog in national parks of mainland Portugal and the Madeira Island. All fleas were tested for the presence of bacteria of the genera Rickettsia and Bartonella using PCR assays. In fleas from mainland Portugal, we detected Rickettsia felis in one Archaeopsylla erinacei maura flea and in one Ctenophtalmus sp. In five Leptopsylla segnis fleas taken from rats in the Madeira Island, we identified Rickettsia typhi. In addition, in four fleas from the genera Ornithophaga and Stenoponia collect from mice and a rat in mainland Portugal, we detected the presence of two new Bartonella genotypes closely related to Bartonella elizabethae. Our findings emphasize the potential risk of flea-transmitted infections in mainland Portugal and the Madeira archipelago, and extend our knowledge of the potential flea vectors of human pathogens.
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An experimental model of human body louse infection with Rickettsia typhi.
Annals of the New York Academy of Sciences, 2003Co-Authors: Linda Houhamdi, Pierre-edouard Fournier, Rong Fang, Didier RaoultAbstract:: Murine (endemic) typhus caused by Rickettsia typhi, one of the most widely distributed arthropod-borne diseases, is transmitted to humans mainly by the oriental rat flea. The human body louse, Pediculus humanus corporis, has been suspected to have a role in the transmission of R. typhi to humans. To evaluate the potential role of Pediculus humanus corporis as a vector of murine typhus, we used R. typhi in an experimental model of human body louse infection previously used with R. prowazekii. A rabbit was made bacteremic by inoculating it with 2 × 106 plaque-forming units of R. typhi; it remained bacteremic for at least 59 hours. Two hundred body lice infected by feeding on the bacteremic rabbit were compared to 200 uninfected control lice. Each louse population was fed once a day on the abdomen of a seronegative rabbit. On day 8 post-infection, as a result of disruption of the gut cells and leakage of the blood meal into the hemolymph, four infected lice became bright red and died within four hours. The life span of infected lice was 20 days less than that of the controls. Infected lice did not transmit R. typhi to their progeny (eggs and larvae) as demonstrated by PCR amplification and cell culture. With an immunofluorescence assay, R. typhi was detected in feces from day 7 post-infection, and the organism remained viable in feces for up to 80 days as demonstrated by cell culture. From the 21st day post-infection, the rabbit used to feed the R. typhi-infected lice developed an immunoglobulin response with a titer of 1:50 increasing to 1:200 at the 42nd day post-infection. It showed no clinical signs of infection. The rabbit that was used to feed uninfected lice remained seronegative. Although body lice are not clearly identified vectors of R. typhi, it seems that under certain circumstances they could transmit R. typhi.
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Seroepidemiology of Rickettsia typhi, spotted fever group Rickettsiae, and Coxiella burnetti infection in pregnant women from urban Tanzania.
The American journal of tropical medicine and hygiene, 1997Co-Authors: Nicholas M. Anstey, Didier Raoult, Hervé Tissot Dupont, Christine G. Hahn, Esther D. Mwaikambo, Malcolm I. Mcdonald, Daniel J. SextonAbstract:Immunofluorescent antibody (IFA) testing was performed on sera drawn from 150 pregnant women in the port city of Dar es Salaam, Tanzania. Prevalence of antibodies to Rickettsia typhi was 28%, higher than in any of the 12 other African countries in which serosurveys using IFA testing have been performed. Seroprevalence of antibodies to spotted fever group Rickettsiae antigens was 25.3%, comparable with that found in other sub-Saharan countries endemic for Amblyomma ticks. Only 4.7% of women were seropositive for Coxiella burnetii.
Rapeephan R. Maude - One of the best experts on this subject based on the ideXlab platform.
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Serosurveillance of orientia tsutsugamushi and Rickettsia typhi in Bangladesh
The American Journal of Tropical Medicine and Hygiene, 2014Co-Authors: Ampai Tanganuchitcharnchai, Rapeephan R. Maude, Aniruddha Ghose, M Robed Amin, M. Belalul Islam, Mohammad Ali, M. Shafiqul Bari, M. Ishaque Majumder, Arjen M. DondorpAbstract:Scrub and murine typhus infections are under-diagnosed causes of febrile illness across the tropics, and it is not known how common they are in Bangladesh. We conducted a prospective seroepidemiologic survey across six major teaching hospitals in Bangladesh by using an IgM enzyme-linked immunosorbent assay. Results indicated recent exposure (287 of 1,209, 23.7% seropositive for Orientia tsutsugamushi and 805 of 1,209, 66.6% seropositive for Rickettsia typhi). Seropositive rates were different in each region. However, there was no geographic clustering of seropositive results for both organisms. There was no difference between those from rural or urban areas. Rickettsia typhi seroreactivity was positively correlated with age. Scrub typhus and murine typhus should be considered as possible causes of infection in Bangladesh.
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Short Report: Serosurveillance of Orientia tsutsugamushi and Rickettsia typhi in Bangladesh
2014Co-Authors: Ampai Tanganuchitcharnchai, Rapeephan R. Maude, Aniruddha Ghose, M Robed Amin, M. Shafiqul Bari, M. Ishaque Majumder, M. Belalul, Mohammad Yeakub Ali, Arjen M. DondorpAbstract:Scrub and murine typhus infections are under-diagnosed causes of febrile illness across the tropics, and it is not known how common they are in Bangladesh. We conducted a prospective seroepidemiologic survey across six major teaching hospitals in Bangladesh by using an IgM enzyme-linked immunosorbent assay. Results indicated recent exposure (287 of 1,209, 23.7% seropositive for Orientia tsutsugamushi and 805 of 1,209, 66.6% seropositive for Rickettsia typhi). Seropositive rates were different in each region. However, there was no geographic clustering of seropositive results for both organisms. There was no difference between those from rural or urban areas. Rickettsia typhi seroreactivity was positively correlated with age. Scrub typhus and murine typhus should be considered as possible causes of infection in Bangladesh.
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SEROSURVEY OF O. TSUTSUGAMUSHI AND R. typhi IN BANGLADESH Short Report: Serosurveillance of Orientia tsutsugamushi and Rickettsia typhi in Bangladesh
2014Co-Authors: Rapeephan R. Maude, Ampai Tanganuchitcharnchai, Aniruddha Ghose, M Robed Amin, M. Shafiqul Bari, M. Ishaque Majumder, Arjen M. Dondorp, Mohammad Yeakub Ali, Richard J. Maude, Daniel H. ParisAbstract:Scrub and murine typhus infections are under-diagnosed causes of febrile illness across the tropics, and it is not known how common they are in Bangladesh. We conducted a prospective seroepidemiologic survey across six major teaching hospitals in Bangladesh by using an IgM enzyme-linked immunosorbent assay. Results indicated recent exposure (324 of 1,244, 26% seropositive for Orientia tsutsugamushi and 840 of 1,244, 67.5% seropositive for Rickettsia typhi). Seropositive rates were different in each region. However, there was no geographic clustering of seropositive results for both organisms. There was no difference between those from rural or urban areas. Rickettsia typhi seroreactivity was positively correlated with age. Scrub typhus and murine typhus should be considered as possible causes of infection in Bangladesh. The etiology of febrile illness remains poorly characterized in many places in the developing world. The causative pathogens are usually not identified and patients are often treated empirically with antimicrobial chemotherapy. Although the burden of some infections is believed to be substantial (e.g., enteric fever), many others, including scrub and murine typhus, are less well described and frequently under-diagnosed. 1,2 Scrub typhus is caused by Orientia tsutsugamushi, an obligate intracellular bacterium transmitted by the bite of larval trombiculid mites (chiggers) (Leptotrombidium spp). This disease is endemic to Asia, the Pacific region, and Australia. In Southeast Asia alone, an estimated one million cases of scrub typhus occur annually, and there are 50,000–80,000 deaths per year caused by this disease, 3 although this number of deaths is probably an
