Evidence that the intra-amoebal Legionella drancourtii acquired a sterol reductase gene from eukaryotes

<p>Abstract</p> <p>Background</p> <p>Free-living amoebae serve as a natural reservoir for some bacteria that have evolved into «amoeba-resistant» bacteria. Among these, some are strictly intra-amoebal, such as <it>Candidatus </it>"Protochlamydia amoebophila" (<it>Candidatus </it>"P. amoebophila"), whose genomic sequence is available. We sequenced the genome of <it>Legionella drancourtii </it>(<it>L. drancourtii</it>), another recently described intra-amoebal bacterium. By comparing these two genomes with those of their closely related species, we were able to study the genetic characteristics specific to their amoebal lifestyle.</p> <p>Findings</p> <p>We identified a sterol delta-7 reductase-encoding gene common to these two bacteria and absent in their relatives. This gene encodes an enzyme which catalyses the last step of cholesterol biosynthesis in eukaryotes, and is probably functional within <it>L. drancourtii </it>since it is transcribed. The phylogenetic analysis of this protein suggests that it was acquired horizontally by a few bacteria from viridiplantae. This gene was also found in the <it>Acanthamoeba polyphaga Mimivirus </it>genome, a virus that grows in amoebae and possesses the largest viral genome known to date.</p> <p>Conclusion</p> <p><it>L. drancourtii </it>acquired a sterol delta-7 reductase-encoding gene of viridiplantae origin. The most parsimonious hypothesis is that this gene was initially acquired by a <it>Chlamydiales </it>ancestor parasite of plants. Subsequently, its descendents transmitted this gene in amoebae to other intra-amoebal microorganisms, including <it>L. drancourtii </it>and <it>Coxiella burnetii</it>. The role of the sterol delta-7 reductase in prokaryotes is as yet unknown but we speculate that it is involved in host cholesterol parasitism.</p

Evidence that the intra-amoebal Legionella drancourtii acquired a sterol reductase gene from eukaryotes

<p>Abstract</p> <p>Background</p> <p>Free-living amoebae serve as a natural reservoir for some bacteria that have evolved into «amoeba-resistant» bacteria. Among these, some are strictly intra-amoebal, such as <it>Candidatus </it>"Protochlamydia amoebophila" (<it>Candidatus </it>"P. amoebophila"), whose genomic sequence is available. We sequenced the genome of <it>Legionella drancourtii </it>(<it>L. drancourtii</it>), another recently described intra-amoebal bacterium. By comparing these two genomes with those of their closely related species, we were able to study the genetic characteristics specific to their amoebal lifestyle.</p> <p>Findings</p> <p>We identified a sterol delta-7 reductase-encoding gene common to these two bacteria and absent in their relatives. This gene encodes an enzyme which catalyses the last step of cholesterol biosynthesis in eukaryotes, and is probably functional within <it>L. drancourtii </it>since it is transcribed. The phylogenetic analysis of this protein suggests that it was acquired horizontally by a few bacteria from viridiplantae. This gene was also found in the <it>Acanthamoeba polyphaga Mimivirus </it>genome, a virus that grows in amoebae and possesses the largest viral genome known to date.</p> <p>Conclusion</p> <p><it>L. drancourtii </it>acquired a sterol delta-7 reductase-encoding gene of viridiplantae origin. The most parsimonious hypothesis is that this gene was initially acquired by a <it>Chlamydiales </it>ancestor parasite of plants. Subsequently, its descendents transmitted this gene in amoebae to other intra-amoebal microorganisms, including <it>L. drancourtii </it>and <it>Coxiella burnetii</it>. The role of the sterol delta-7 reductase in prokaryotes is as yet unknown but we speculate that it is involved in host cholesterol parasitism.</p

Tick-borne rickettsioses in international travellers

AbstractBackground: Tick-borne rickettsioses are of emerging importance in today’s travel medicine but have until recently received little attention. We describe the current knowledge of tick-borne rickettsioses as they relate to international travel, their microbiological diagnosis, treatment, possible prevention, and future prospects.Methods: Literature-based review and personal observations.Results: During the last decade, some 400 cases of tick-borne rickettsioses have been reported in international travellers, the vast majority being African tick bite fever caused by Rickettsia africae and Mediterranean spotted fever caused by Rickettsia conorii. Only a minority of infected travellers can recall a preceding tick bite. Most patients present with a mild-to-moderately severe flu-like illness typically accompanied by a cutaneous rash and an inoculation eschar at the site of the tick bite, but potentially life-threatening disease with disseminated vaculitis is occasionally seen. Definite microbiological confirmation of tick-borne rickettsioses by isolation or antigen detection is only available at reference laboratories and diagnosis must in most cases rely on clinical and epidemiological data supported by serology. Doxycycline is the recommended treatment for tick-borne rickettsioses and prevention is based on personal protective measures against tick bites when travelling in endemic areas.Conclusion: Tick-borne rickettsiosis should be suspected in febrile returnees from endemic areas, especially in cases with skin eruptions. Travellers to endemic areas should be encouraged to use personal protective measures against tick bites

Histologic Features and Immunodetection of African Tick-bite Fever Eschar

Immunohistochemical detection of rickettsial antigens may be useful in diagnosis

Sca1, a previously undescribed paralog from autotransporter protein-encoding genes in Rickettsia species

BACKGROUND: Among the 17 genes encoding autotransporter proteins of the "surface cell antigen" (sca) family in the currently sequenced Rickettsia genomes, ompA, sca5 (ompB) and sca4 (gene D), have been extensively used for identification and phylogenetic purposes for Rickettsia species. However, none of these genes is present in all 20 currently validated Rickettsia species. Of the remaining 14 sca genes, sca1 is the only gene to be present in all nine sequenced Rickettsia genomes. To estimate whether the sca1 gene is present in all Rickettsia species and its usefulness as an identification and phylogenetic tool, we searched for sca1genes in the four published Rickettsia genomes and amplified and sequenced this gene in the remaining 16 validated Rickettsia species. RESULTS: Sca1 is the only one of the 17 rickettsial sca genes present in all 20 Rickettsia species. R. prowazekii and R. canadensis exhibit a split sca1 gene whereas the remaining species have a complete gene. Within the sca1 gene, we identified a 488-bp variable sequence fragment that can be amplified using a pair of conserved primers. Sequences of this fragment are specific for each Rickettsia species. The phylogenetic organization of Rickettsia species inferred from the comparison of sca1 sequences strengthens the classification based on the housekeeping gene gltA and is similar to those obtained from the analyses of ompA, sca5 and sca4, thus suggesting similar evolutionary constraints. We also observed that Sca1 protein sequences have evolved under a dual selection pressure: with the exception of typhus group rickettsiae, the amino-terminal part of the protein that encompasses the predicted passenger domain, has evolved under positive selection in rickettsiae. This suggests that the Sca1 protein interacts with the host. In contrast, the C-terminal portion containing the autotransporter domain has evolved under purifying selection. In addition, sca1 is transcribed in R. conorii, and might therefore be functional in this species. CONCLUSION: The sca1 gene, encoding an autotransporter protein that evolves under dual evolution pressure, is the only sca-family gene to be conserved by all Rickettsia species. As such, it is a valuable identification target for these bacteria, especially because rickettsial isolates can be identified by amplification and sequencing of a discriminatory gene fragment using a single primer pair. It may also be used as a phylogenetic tool. However, its current functional status remains to be determined although it was found expressed in R. conorii

Molecular and cultural analysis of the bacterial flora associated with brain abscesses

Les abcès cérébraux sont des infections potentiellement mortelles, entraînant souvent des séquelles graves. La prise en charge médicale en reste empirique en raison d un manque de connaissance approfondie des microorganismes responsables de cette condition. Dans la plupart des laboratoires microbiologiques, le diagnostic d abcès cérébral est basé sur la culture du pus recueilli chirurgicalement. Malheureusement, cette procédure a de nombreuses limites et ne permet l identification que d une petite partie de la population microbienne en cause. L amplification par PCR et le séquençage du gène codant la fraction 16S de l ADN ribosomal ont récemment été utilisées pour surmonter les limites de la culture, et ont été démontré leur efficacité dans la documentation des infections bactériennes. Malheureusement, cette procédure présente un degré de discrimination limité en cas d infection polymicrobienne. Des études métagénomiques de flores complexes de l homme, basées sur une combinaison de PCR, clonage et séquençage des produits de PCR se sont avérées utiles pour évaluer la diversité bactérienne des flores dentaires, vaginales et intestinales. Nous avons appliqué cette technique à des échantillons d abcès cérébral pour étudier la flore associée à cette maladie. Dans une première étape, nous avons réalisé une enquête en utilisant la culture et les techniques moléculaires. Le but de cette étude était d analyser et d évaluer les bactéries de la flore responsable des abcès cérébraux, en comparant la culture à trois techniques moléculaires basées sur le gène 16S rDNA, incluant le séquençage direct, le clonage suivi de séquençage par méthode de Sanger, et le séquençage direct des produits de PCR par pyroséquençage. Cette enquête a déterminé que la variété des espèces bactériennes associée aux abcès cérébraux est beaucoup plus grande que précédemment décrite, et inclut de nombreuses bactéries anaérobies et des bactéries incultivables de la flore buccale. Cette étude préliminaire a identifié 49 agents bactériens différents, et a permis l identification de 27 bactéries jamais détectées auparavant dans des abcès du cérébraux, dont 15 n avaient jamais été cultivées. Un tel nombre d espèces bactériennes impliquées dans les abcès cérébraux a motivé l étude de 51 nouveaux spécimens dans le but de décrire plus en détail la flore associée aux abcès cérébraux en fonction de leurs étiologies. Ainsi, nous avons effectué une analyse métagénomique, basé sur le gène 16S rDNA, de 51 patients ayant développé un abcès cérébral. Notre stratégie a été beaucoup plus discriminatoire et a permis à l identification d un plus grand nombre de bactéries que la culture et l amplification et le séquençage direct de l ANRr 16S. La combinaison des données de 71 patients (20 de la première étude et 51 de la deuxième étude) a permis l identification de plusieurs associations à l aide de la méthode de data mining.En outre, notre étude a permis l identification de deux nouvelles bactéries, la première étant une nouvelle espèce de genre Staphylococcus (Staphylococcus massiliensis) et la seconde étant une bactérie anaérobie qui représente une nouvelle espèce dans un nouveau genre au sein du phylum des Bacteroidetes (Phocaeicola abscesses). En outre, nous avons décrit deux cas inhabituels d abcès du cerveau, à Mycoplasma hominis après curetage utérin, et à Nocardia carnea chez un greffé rénal. Malgré les limites inhérentes à la procédure de clonage, nos résultats suggèrent que le clonage et le séquençage de gène DNAr 16S est une méthode très performante pour identifier les agents bactériens associés aux abcès cérébraux.Brain abscess is a life-threatening infection with frequent serious sequelae. The medical management remains empirical due to a lack of comprehensive knowledge of the microorganisms responsible for this condition. In most microbiology laboratories the diagnosis of brain abscess is based on culture from pus collected surgically. Unfortunately, this procedure has many limitations and reveals only a small portion of the true microbial population. PCR-amplified 16S rDNA sequencing has recently been used to overcome the limitations of culture-based bacterial detection in brain abscess pus, and it was demonstrated to be effective in the documentation of monomicrobial infections. Unfortunately, this procedure failed to discriminate among polymicrobial floras.Metagenomic studies of complex human floras using a combination of 16S rDNA PCR and cloning-sequencing of PCR products proved useful to evaluate the bacterial diversity of dental, vaginal and intestinal floras. Thus, we applied this technique to brain abscess samples to study the flora associated with this condition. In a first step, we performed an investigation using culture and molecular techniques. The purpose of this investigation was to analyze and evaluate the bacterial flora responsible for brain abscess by comparing standard culture technique to three techniques using 16S rDNA amplification, that is, direct sequencing, multiple sequencing following cloning, and multiple sequencing via high throughput pyrosequencing. This investigation has determined that the variety of brain abscess-associated bacterial species is much larger than previously reported, and it includes many anaerobes and uncultured bacteria from the oral cavity flora. This preliminary study identified 49 distinct brain abscess bacterial agents, and enabled the identification of 27 bacteria never detected before in brain abscess, 15 of which were uncultured.Such a high number of bacterial species involved in brain abscess prompted the study of 51 new specimens in an effort to describe further the flora associated with brain abscesses and their etiologies. Thus, we performed a 16S rDNA-based metagenomic analysis of cerebral abscesses from 51 patients. Our strategy was significantly more discriminatory and enabled the identification of greater number of bacterial taxa, than culture and conventional 16S rDNA PCR/sequencing, respectively. The combination of data from 71 patients (20 from the first study and 51 from the second study) enabled the identification of several associations using the data mining analysis. Also, these studies permitted the identification of two novel bacteria, the first being a novel Staphylococcus species (Staphylococcus massiliensis) and the second being a novel anaerobic bacterium that represents a novel species in a new genus within the phylum Bacteroidetes (Phocaeicola abscesses). In addition, we reported tow unusual cases of brain abscess, the first case was a Mycoplasma hominis brain abscess following uterus curettage and the second case was a Nocardia carnea infection in a kidney transplant recipient patient.Despite limitations inherent to the cloning procedure, our results suggest that cloning and sequencing of PCR-amplified 16S rDNA is a highly valuable method to identify bacterial agents of brain abscesses.AIX-MARSEILLE2-Bib.electronique (130559901) / SudocSudocFranceF

Absence of antibodies to Rickettsia spp., Bartonella spp., Ehrlichia spp. and Coxiella burnetii in Tahiti, French Polynesia

International audienceAbtractBackgroundIn the Pacific islands countries and territories, very little is known about the incidence of infectious diseases due to zoonotic pathogens. To our knowledge, human infections due to Rickettsia spp., Coxiella burnetii, Ehrlichia spp. and Bartonella spp. have never been reported in French Polynesia; and infections due to C. burnetti have been reported worldwide except in New Zealand. To evaluate the prevalence of this disease, we conducted a serosurvey among French Polynesian blood donors.MethodsThe presence of immunoglobulin G antibodies against R. felis, R. typhi, R. conorii, C. burnetii, B. henselae, B. quintana, and E. chaffeensis was evaluated by indirect immunofluorescence assay in sera from 472 French Polynesian blood donors collected from 2011 to 2013. In addition, 178 ticks and 36 cat fleas collected in French Polynesia were also collected and tested by polymerase chain reaction to detect Rickettsia spp., B. henselae and Ehrlichia spp.ResultsNone of the blood donors had antibodies at a significant level against Rickettsia spp., Coxiella burnetii, Ehrlichia spp. and Bartonella spp. All tested ticks and cat fleas were PCR-negative for Rickettsia spp., B. henselae, and Ehrlichia spp.ConclusionWe cannot conclude that these pathogens are absent in French Polynesia but, if present, their prevalence is probably very low. C. burnetii has been reported worldwide except in New Zealand. It may also be absent from French Polynesia