PCR amplification and phylogenetic analysis of groESL operon sequences from Ehrlichia ewingii and Ehrlichia muris

Using next generation sequencing for molecular detection and differentiation of Anaplasma phagocytophilum variants from host seeking Ixodes scapularis ticks in the United States

Anaplasmosis is increasingly common in the United States, with cases being reported over an expanding geographic area. To monitor for changes in risk of human infection, the U.S. Centers for Disease Control and Prevention monitors the distribution and abundance of host-seeking vector ticks (Ixodes scapularis and Ixodes pacificus) and their infection with Anaplasma phagocytophilum. While several variants of A. phagocytophilum circulate in I. scapularis, only the human-active variant (Ap-ha) appears to be pathogenic in humans. Failure to differentiate between human and non-human variants may artificially inflate estimates of the risk of human infection. Efforts to differentiate the Ap-ha variant from the deer variant (Ap-V1) in ticks typically rely on traditional PCR assays coupled with sequencing of PCR products. However, laboratories are increasingly turning to Next Generation Sequencing (NGS) to increase testing efficiency, retain high sensitivity, and increase specificity compared with traditional PCR assays. We describe a new NGS assay with novel targets that accurately segregate the Ap-ha variant from other non-human variants and further identify unique clades within the human and non-human variants. Recognizing that not all investigators have access to NGS technology, we also developed a PCR assay based on one of the novel targets so that variants can be visualized using agarose gel electrophoresis without the need for subsequent sequencing. Such an assay may be used to improve estimates of human risk of developing anaplasmosis in North America.

A new genetic approach to distinguish strains of Anaplasma phagocytophilum that appear not to cause human disease

Genetic diversity of Anaplasma phagocytophilum was assessed in specimens from 16 infected patients and 16 infected Ixodes scapularis ticks. A region immediately downstream of the 16S rRNA gene, which included the gene encoding SdhC, was sequenced. For the A. phagocytophilum strains from patients no sequence differences were detected in this region. In contrast, significantly fewer ticks had a sequence encoding SdhC that was identical to that of the human strains (11/16 vs. 16/16, p = 0.04). This variation is consistent with the premise that not all A. phagocytophilum strains present in nature are able to cause clinical illness in humans. A strain referred to as A. phagocytophilumVariant-1 that is regarded as non-pathogenic for humans was previously described using a different typing method. Data from the current study suggest that both typing methods are identifying the same non-pathogenic strains.

Species and Genetic Diversity of Representatives of the <i>Anaplasmataceae</i> Family Found in the Sympatry Zone of the <i>Ixodes, Dermacentor</i> and <i>Haemaphysalis</i> Genera Ticks

Introduction.On the territory of the Ekhirit-Bulagatsky district of the Irkutsk region zones of sympatry of four Ixodes ticks species are found, where the species and genetic diversity of infectious agents transmitted through tick bites may be more pronounced than in foci with a mono-dominant type of ticks’ population. In this connection, the study of the species and genetic diversity of representatives of the Anaplasmataceae family in the sympatry zone of the Ixodes ticks of closely related species was of scientific interest.

Objective: To study the species and genetic diversity of members of the Anaplasmataceae family in the zones of sympatry of Ixodes ticks Ixodes persulcatus, Dermacentor silvarum, D. nuttalli and Haemaphysalis concinna, to identify the main carriers and potential reservoir hosts of ehrlichia and anaplasma.

Methods. In the course of the study, 1106 specimens of adult ticks and 49 samples of small mammalian livers from the Ekhirit-Bulagatsky area were analyzed. Anaplasma and ehrlichia DNA were detected by two-round PCR in the presence of genus- and species-specific primers from the 16S rRNA gene region. The nucleotide sequences of the 16S rRNA gene and the fragment of the groESL operon were identified in some samples. Sequencing was carried out according to the Sanger method. Comparative analysis was performed using the BLASTN program and ClustalW method. Epidemiological data analysis was performed using parametric methods of statistical processing of the material.

Results. The DNA of Ehrlichia muris and Anaplasma phagocytophilum were detected in all studied species of ticks in their sympatry area. However, the rate of infection of taiga ticks was significantly higher than that of H. concinna and Dermacentor spp. Potential reservoir hosts of the Anaplasmataceae family members can be classified as Microtus oeconomus, M. gregalis, Myodes rutilus and Sorex spp. When analyzing the nucleotide sequences of the 16S rRNA gene, three genetic variants of anaplasma were detected. The nucleotide sequences of the A. phagocytophilum groESL operon belonged to two genetic groups.

MyD88-dependent inflammasome activation and autophagy inhibition contributes to Ehrlichia-induced liver injury and toxic shock

Severe hepatic inflammation is a common cause of acute liver injury following systemic infection with Ehrlichia, obligate Gram-negative intracellular bacteria that lack lipopolysaccharide (LPS). We have previously shown that type I IFN (IFN-I) and inflammasome activation are key host-pathogenic mediators that promote excessive inflammation and liver damage following fatal Ehrlichia infection. However, the underlying signals and mechanisms that regulate protective immunity and immunopathology during Ehrlichia infection are not well understood. To address this issue, we compared susceptibility to lethal Ixodes ovatus Ehrlichia (IOE) infection between wild type (WT) and MyD88-deficient (MyD88^-/-) mice. We show here that MyD88^-/- mice exhibited decreased inflammasome activation, attenuated liver injury, and were more resistant to lethal infection than WT mice, despite suppressed protective immunity and increased bacterial burden in the liver. MyD88-dependent inflammasome activation was also dependent on activation of the metabolic checkpoint kinase mammalian target of rapamycin complex 1 (mTORC1), inhibition of autophagic flux, and defective mitophagy in macrophages. Blocking mTORC1 signaling in infected WT mice and primary macrophages enhanced bacterial replication and attenuated inflammasome activation, suggesting autophagy promotes bacterial replication while inhibiting inflammasome activation. Finally, our data suggest TLR9 and IFN-I are upstream signaling mechanisms triggering MyD88-mediated mTORC1 and inflammasome activation in macrophages following Ehrlichia infection. This study reveals that Ehrlichia-induced liver injury and toxic shock are mediated by MyD88-dependent inflammasome activation and autophagy inhibition.

Human monocytic ehrlichiosis (HME) is the most prevalent emerging infectious disease in the United States. Ehrlichia chaffeensis, etiologic agent of HME, is a Gram negative obligate intracellular bacterium transmitted by infected tick bites and can infect different cell type. Although Ehrlichia lack lipopolysaccharide (LPS), they induce potentially life threatening HME that mimic sepsis or toxic shock associated with multi-organ failure. The clinical diagnosis of HME is difficult, and definitive diagnosis is most often retrospective. Late antibiotic treatment is frequently ineffective in preventing disease progression to fatal multi-organ failure. Liver failure is one of the most serious complications and the most frequent cause of death in patients with HME, however we only have a limited understanding of how this liver failure is caused during fatal Ehrlichia infection. The objective of this study is to determine how LPS-negative Ehrlichia activates inflammatory responses in macrophages during Ehrlichia infection to promote liver damage. We show here that MyD88-signaling causes detrimental derangement of the immune system and subsequent liver damage by regulating two key innate immune events in macrophages: autophagy and inflammasome activation. Targeting host-pathogenic pathways in ehrlichiosis can be incorporated into future design of novel therapeutic approaches for HME.

Development of a generic Ehrlichia FRET-qPCR and investigation of ehrlichioses in domestic ruminants on five Caribbean islands

Background

The Ehrlichia are obligate intracellular Gram-negative tick-borne bacteria that are important human and animal pathogens. There is a need for assays to rapidly and reliably detect and differentiate the five generally recognized species into groups in a single reaction: E. canis, E. chaffeensis, E. ewingii, E. muris and E. ruminantium.

Methods

We developed primers and probes against the 16S rRNA gene to enable us to reliably detect the five major Ehrlichia spp. in a single FRET-qPCR. We tested the Ehrlichia FRET-qPCR on reference strains and on DNA from the blood of domestic ruminants from five Caribbean islands. The Ehrlichia present were determined using melting point analysis and by sequencing the Ehrlichia FRET-qPCR products as well as those of a nested PCR against the citrate synthase gene (gltA).

Results

Our Ehrlichia FRET-qPCR was negative for the closely related Anaplasma marginale and A. phagocytophilum but gave positive reactions with reference strains of the most generally recognized species and with other less characterized Ehrlichia of domestic ruminants, mainly E. ovina, the Panola Mountain Ehrlichia, and Ehrlichia sp. BOV2010. Melting point analysis revealed 4 distinct groups: E. ruminantium (T_m ~55.8 °C); E. chaffeensis and E. ewingii (T_m ~57.7 °C); E. canis, E. muris, E. ovina and Ehrlichia sp. BOV 2010 (T_m ~62.0 °C); and the Panola Mountain Ehrlichia (T_m ~65.5 °C). The detection limit of the FRET-qPCR was ~ 5 gene copies in a reaction and the sequences of the FRET-qPCR products were as expected. With DNA from domestic ruminants from the Caribbean we found 12.2 % (134/1,101) positive: cattle (76/385; 19.7 %), sheep (45/340; 13.2 %) and goats (13/376; 3.5 %). Melting point analysis and sequencing of the FRET-qPCR and nested PCR gltA products showed the Ehrlichia we detected were E. canis or very closely related organisms.

Conclusions

In a single reaction, our Ehrlichia FRET-qPCR can detect the Ehrlichia spp. we studied and differentiate them into four groups. Domestic ruminants in the Caribbean are not uncommonly exposed to Ehrlichia, possibly E. canis or very closely related organisms.

PCR-RFLP assay for species and subspecies differentiation of the Streptococcus bovis group based on groESL sequences

The sequence diversity of groESL genes among Streptococcus bovis group isolates was analysed, including five reference strains and 36 clinical isolates. Phylogenetic analysis of the groES and groEL sequences showed that the isolates that belonged to the same species or subspecies usually clustered together. The intergenic spacer region between groES and groEL was variable in size (67–342 bp) and sequence and appeared to be a unique marker for species or subspecies determination. Sequence similarities of the groESL genes among species and subspecies ranged from 84.2 to 99.0 % in groES, and from 88.0 to 99.0 % in groEL. Based on the sequences determined, a Streptococcus bovis group-specific PCR assay was developed, which may provide an alternative means of distinguishing the bovis group from other viridans streptococci. Restriction digestion of the amplicon with AclI further differentiated the species and subspecies.

Identification of 19 polymorphic major outer membrane protein genes and their immunogenic peptides in Ehrlichia ewingii for use in a serodiagnostic assay

Ehrlichia ewingii, a tick-transmitted rickettsia previously known only as a canine pathogen, was recently recognized as a human pathogen. E. ewingii has yet to be cultivated, and there is no serologic test available to diagnose E. ewingii infection. Previously, a fragment (505 bp) of a single E. ewingii gene homologous to 1 of 22 genes encoding Ehrlichia chaffeensis immunodominant major outer membrane proteins 1 (OMP-1s)/P28s was identified. The purposes of the present study were to (i) determine the E. ewingii omp-1 gene family, (ii) determine each OMP-1-specific peptide, and (iii) analyze all OMP-1 synthesized peptides for antigenicity. Using nested touchdown PCR and a primer walking strategy, we found 19 omp-1 paralogs in E. ewingii. These genes are arranged in tandem downstream of tr1 and upstream of secA in a 24-kb genomic region. Predicted molecular masses of the 19 mature E. ewingii OMP-1s range from 25.1 to 31.3 kDa, with isoelectric points of 5.03 to 9.80. Based on comparative sequence analyses among OMP-1s from E. ewingii and three other Ehrlichia spp., each E. ewingii OMP-1 oligopeptide that was predicted to be antigenic, bacterial surface exposed, unique in comparison to the other E. ewingii OMP-1s, and distinct from those of other Ehrlichia spp. was synthesized for use in an enzyme-linked immunosorbent assay. Plasmas from experimentally E. ewingii-infected dogs reacted significantly with most of the OMP-1-specific peptides, indicating that multiple OMP-1s were expressed and immunogenic in infected dogs. The results support the utility of the tailored OMP-1 peptides as E. ewingii serologic test antigens.

Relative importance of T-cell subsets in monocytotropic ehrlichiosis: a novel effector mechanism involved in Ehrlichia-induced immunopathology in murine ehrlichiosis

Infection with gram-negative monocytotropic Ehrlichia strains results in a fatal toxic shock-like syndrome characterized by a decreased number of Ehrlichia-specific CD4(+) Th1 cells, the expansion of tumor necrosis factor alpha (TNF-alpha)-producing CD8(+) T cells, and the systemic overproduction of interleukin-10 (IL-10) and TNF-alpha. Here, we investigated the role of CD4(+) and CD8(+) T cells in immunity to Ehrlichia and the pathogenesis of fatal ehrlichiosis caused by infection with low- and high-dose (10(3) and 10(5) bacterial genomes/mouse, respectively) ehrlichial inocula. The CD4(+) T-cell-deficient mice showed exacerbated susceptibility to a lethal high- or low-dose infection and harbored higher bacterial numbers than did wild-type (WT) mice. Interestingly, the CD8(+) T-cell-deficient mice were resistant to a low dose but succumbed to a high dose of Ehrlichia. The absence of CD8(+) T cells abrogated TNF-alpha and IL-10 production, reduced tissue injury and bacterial burden, restored splenic CD4(+) T-cell numbers, and increased the frequency of Ehrlichia-specific CD4(+) Th1 cells in comparison to infected WT mice. Although fatal disease is perforin independent, our data suggested that perforin played a critical role in controlling bacterial burden and mediating liver injury. Similar to WT mice, mortality of infected perforin-deficient mice was associated with CD4(+) T-cell apoptosis and a high serum concentration of IL-10. Depletion of IL-10 restored the number of CD4(+) and CD8(+) T cells in infected WT mice. Our data demonstrate a novel mechanism of immunopathology in which CD8(+) T cells mediate Ehrlichia-induced toxic shock, which is associated with IL-10 overproduction and CD4(+) T-cell apoptosis.

Contribution of polymorphisms in ankA, gltA, and groESL in defining genetic variants of Anaplasma phagocytophilum

Analysis of several nucleotide polymorphisms in polymorphic genes (ankA, gltA, and groESL) from 16S rRNA gene-based genetic variants of Anaplasma phagocytophilum from dogs in the western United States defined at least two sets of multigene polymorphisms to further characterize these variants. The multigene polymorphism approach holds promise for development of a genotyping scheme for this important pathogen.

Balancing protective immunity and immunopathology: a unifying model of monocytotropic ehrlichiosis

Interactions among pathogens, antigen-presenting cells (APCs) and lymphocytes are critical in maintaining balance in the daily challenges to the immune system. Monocytotropic ehrlichiosis, caused by Ehrlichia chaffeensis, is a multisystem inflammatory ailment. A complex interaction between Ehrlichia and the immune systems of a number of mammalian hosts, in human disease and animal models, has been described. The presence of an overwhelming ehrlichial infection in immunocompromised individuals suggests that severe tissue damage is most likely due to direct bacterial effect. However, clinical and experimental observations indicate that this is an oversimplified concept. First, immunocompetent patients with severe ehrlichiosis have a low bacterial burden. Second, severe and fatal murine ehrlichiosis in immunocompetent animals, which mimics human disease, is associated with a low bacterial burden in different organs and late systemic and local overproduction of TNF-alpha by T cells. In order to counterbalance overshooting immune responses, T cells and APCs secrete anti-inflammatory cytokines that are key for maintaining a healthy balance between protection and immunopathology. CD4+ T cell-mediated immunity and antibody responses of a Th1 phenotype play critical roles in protection against Ehrlichia. Of particular importance for the generation of protective immunity is the induction of activation programs in APCs directly by pathogens or by T cell-derived factors. In this study, we consider the roles of innate and adaptive immune responses in terms of protection from severe ehrlichiosis and their potential roles in immunopathology.

Role of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 in the pathogenesis of severe murine monocytotropic ehrlichiosis: increased resistance of TNF receptor p55- and p75-deficient mice to fatal ehrlichial infection

Intraperitoneal (i.p.) infection with a high dose of a highly virulent Ehrlichia strain (IOE) results in a toxic shock-like syndrome characterized by severe liver injury and systemic overproduction of tumor necrosis factor alpha (TNF-alpha) by CD8+ T cells. We examined the role of TNF-alpha and TNF receptors in high-dose-IOE-induced shock/liver injury. TNF receptor (TNFR) I/II-/- mice lacking both the p55 and p75 receptors for this cytokine were more resistant to IOE-induced liver injury than their wild-type background controls. TNFR I/II-/- mice survived longer, dying between 15 and 18 days, with evidence of mild liver necrosis/apoptosis. In contrast, wild-type mice were not rescued from the lethal effect of IOE by TNF-alpha neutralization. TNF-alpha-depleted mice developed severe liver injury and succumbed to disease between days 9 and 11 postinfection, similar to sham-treated, infected wild-type mice. Although IFN-gamma production in the spleens of IOE-infected TNFR I/II-/- and TNF-alpha-depleted mice was higher than that detected in wild-type controls, these mice had higher bacterial burdens than infected controls. Following high-dose IOE challenge, TNFR I/II-/- and TNF-alpha-depleted mice have an early increase in IL-10 levels in sera and spleens, which was produced mainly by adherent spleen cells. In contrast, a late burst of interleukin-10 (IL-10) was observed in control mice. Nonadherent spleen cells were the major source of IL-10 in IOE-infected wild-type mice. We conclude that TNFR I/II and TNF-alpha participate in Ehrlichia-induced shock and host defense by regulating liver injury and controlling ehrlichial burden. Our data suggest that fatal ehrlichiosis could be a multistep process, where TNF-alpha is not solely responsible for mortality.

A real-time combined polymerase chain reaction assay for the rapid detection and differentiation of Anaplasma phagocytophilum, Ehrlichia chaffeensis, and Ehrlichia ewingii

A rapid real-time polymerase chain reaction (PCR) assay capable of the simultaneous detection and differentiation of Anaplasma phagocytophilum, Ehrlichia chaffeensis, and Ehrlichia ewingii was developed using the LightCyclertrade mark instrument (Roche Applied Sciences, Indianapolis, IN). The assay targets the operon groEL of the heat shock protein. Base pair mismatches in amplified DNA in regions of detection probe hybridization allowed organism differentiation by melting curve analysis. The analytical sensitivity was at least 10 copies per reaction. DNA extracts from 59 specimens previously confirmed positive for A. phagocytophilum (n = 37), E. chaffeensis (n = 19), or E. ewingii (n = 3) were used to evaluate the assay. All of the specimens positive for 1 of the 3 organisms by conventional PCR were likewise positive by the LightCycler method. Sensitivity and specificity were at least 100% compared with conventional PCR. This assay provides a rapid method for the detection and differentiation of the causative agents of human ehrlichiosis in the United States.

Identification of clinically relevant enterococcus species by direct sequencing of groES and spacer region

We determined the groESL sequences (groES, groEL, and the intergenic spacer) of 10 clinically relevant Enterococcus species and evaluated the feasibility of identifying Enterococcus species on the basis of these sequences. Seven common clinical Enterococcus species, E. faecalis, E. faecium, E. casseliflavus, E. gallinarum, E. avium, E. raffinosus, and E. hirae, and three less common Enterococcus species, E. cecorum, E. durans, and E. mundtii, were examined in this study. We found that the groES genes of these enterococcal species are identical in length (285 nucleotides) and contain an unusual putative start codon, GTG. The lengths and sequences of the intergenic regions (spacers between the groES and groEL genes) are quite variable (17 to 57 bp in length) among Enterococcus species but are conserved in strains within each species, with only a few exceptions. Considerable variation of groES or groEL sequences was also observed. The evolutionary trees of groES or groEL sequences revealed similarities among Enterococcus species. However, the overall intraspecies variation of groES was less than that of groEL. The high interspecies variation and low intraspecies variation indicate that the groES and spacer sequences are more useful than groEL for identification of clinically relevant Enterococcus species. The sequences of these two genetic traits, groES and spacer, can be determined by a single PCR and direct sequencing and may provide important information for the differentiation of closely related species of Enterococcus.

Ultrastructure and phylogenetic analysis of 'Candidatus Neoehrlichia mikurensis' in the family Anaplasmataceae, isolated from wild rats and found in Ixodes ovatus ticks

A novel bacterium that infects laboratory rats was isolated from wild Rattus norvegicus rats in Japan. Transmission electron microscopy of the spleen tissue revealed small cocci surrounded by an inner membrane and a thin, rippled outer membrane in a membrane-bound inclusion within the cytoplasm of endothelial cells. Phylogenetic analysis of the 16S rRNA gene sequence of the bacterium found in R. norvegicus rats and Ixodes ovatus ticks in Japan revealed that the organism represents a novel clade in the family Anaplasmataceae, which includes the Schotti variant found in Ixodes ricinus ticks in the Netherlands and the Ehrlichia-like Rattus strain found in R. norvegicus rats from China. The novel clade was confirmed by phylogenetic analysis of groESL sequences found in R. norvegicus rats and Ixodes ovatus ticks in Japan. No serological cross-reactivity was detected between this bacterium and members of the genera Anaplasma, Ehrlichia or Neorickettsia in the family Anaplasmataceae. It is proposed that this new cluster of bacteria should be designated 'Candidatus Neoehrlichia mikurensis'.

Overproduction of TNF-α by CD8+Type 1 Cells and Down-Regulation of IFN-γ Production by CD4+Th1 Cells Contribute to Toxic Shock-Like Syndrome in an Animal Model of Fatal Monocytotropic Ehrlichiosis

Human monocytotropic ehrlichiosis (HME) is an emerging, life-threatening, infectious disease caused by Ehrlichia chaffeensis, an obligate intracellular bacterium that lacks cell wall LPS. We have previously developed an animal model of severe HME using a strain of Ehrlichia isolated from Ixodes ovatus ticks (IOE). To understand the basis of susceptibility to severe monocytotropic ehrlichiosis, we compared low and high doses of the highly virulent IOE strain and the less virulent Ehrlichia muris strain that are closely related to E. chaffeensis in C57BL/6 mice. Lethal infections caused by high or low doses of IOE were accompanied by extensive liver damage, extremely elevated levels of TNF-alpha in the serum, high frequency of Ehrlichia-specific, TNF-alpha-producing CD8(+) T cells in the spleen, decreased Ehrlicha-specific CD4(+) T cell proliferation, low IL-12 levels in the spleen, and a 40-fold decrease in the number of IFN-gamma-producing CD4(+) Th1 cells. All groups contained negligible numbers of IL-4-producing cells in the spleen. Transfer of Ehrlichia-specific polyclonal Abs and IFN-gamma-producing Ehrlichia-specific CD4(+) and CD8(+) type 1 cells protected naive mice against lethal IOE challenge. Interestingly, infection with high dose E. muris provided protection against rechallenge with a lethal dose of IOE. Cross-protection was associated with substantial expansion of IFN-gamma-producing CD4(+) and CD8(+) cells, but not TNF-alpha-producing CD8(+) T cells, a high titer of IgG2a, and a low serum level of TNF-alpha. In conclusion, uncontrolled TNF-alpha production by CD8(+) T cells together with a weak CD4(+) Th1 cell response are associated with immunopathology and failure to clear IOE in the fatal model of HME.

Phylogenetic relationships among Ehrlichia ruminantium isolates

Ehrlichia ruminantium, the causative agent of heartwater, is a tick-borne pathogen infecting ruminants throughout sub-Saharan Africa and on some Caribbean islands. The most reliable test for E. ruminantium is PCR-based, but this gives positive results in some areas free of clinical heartwater and of the known Amblyomma spp. tick vectors. To investigate the molecular basis for this finding we have sequenced and carried out phylogenetic analysis of a range of genes from a number of E. ruminantium isolates. The genes include ribonuclease III and cytochrome c oxidase assembly protein genes (the pCS20 region), groESL, citrate synthase (gltA), and 16S ribosomal RNA. Relationships among major antigenic protein (map1) genes have been exhaustively investigated in a previous study that showed that the genes are variable in length, have non-synonymous mutations, and show no geographical specificity among isolates. The 16S sequences are highly conserved, except in the V1 loop region. The pCS20, groESL, and gltA genes show only single nucleotide polymorphisms (SNPs) dispersed throughout the sequenced regions. Phylogenetic analysis using pCS20 data differentiates the western African isolates into a single clade, which also includes a southern African isolate. All other southern African isolates and a Caribbean isolate fall into a further clade, which is subdivided into two groups. Sequence variation within this clade is greater than that within the western African clade, suggesting that E. ruminantium originated in southern Africa.

RNA polymerase beta-subunit-based phylogeny of Ehrlichia spp., Anaplasma spp., Neorickettsia spp. and Wolbachia pipientis

Sequence analysis of rpoB, the gene encoding the beta-subunit of RNA polymerase, was used in a phylogenetic investigation of nine species from the genera Ehrlichia, Neorickettsia, Wolbachia and Anaplasma. The complete nucleotide sequences obtained for Anaplasma phagocytophilum (HGE agent), Ehrlichia chaffeensis, Neorickettsia sennetsu, Neorickettsia risticii, Anaplasma marginale and Wolbachia pipientis were amongst the longest rpoB sequences in GenBank and ranged from 4074 bp for N. sennetsu to 4311 bp for W. pipientis. Additional partial rpoB sequences were obtained for Ehrlichia canis, Ehrlichia ruminantium and Ehrlichia muris. Identical phylogenetic trees were inferred from multiple sequence alignments of the nucleotide sequences and the derived amino acid sequences using either distance, maximum-likelihood or parsimony methods. This study confirms the phylogeny previously inferred from sequence analyses of the 16S rRNA gene, groESL and gltA and allows the confirmation of four monophyletic clades. The rpoB nucleotide sequences were more variable than the 16S rRNA gene and groESL sequences at the species level.

Demonstration of Anaplasma (Ehrlichia) platys inclusions in peripheral blood platelets of a dog in Japan

A free-roaming dog in Okinawa island showed Anaplasma (Ehrlichia) platys-like inclusions within the platelets of peripheral blood samples. The inclusions were positive in indirect fluorescence test with anti-A. phagocytophila serum. The platelet count of the dog was 170,000 microl(-1). The sequence analysis of the 16S rRNA, citrate synthase and heat shock protein genes of DNA from the infected platelets confirmed that the inclusions were A. platys. This is the first detection of A. platys inclusions in dogs in Japan.

Determination of the nucleotide sequences of heat shock operon groESL and the citrate synthase gene (gltA) of Anaplasma (Ehrlichia) platys for phylogenetic and diagnostic studies

The 1,670-bp nucleotide sequence of the heat shock operon groESL and the 1,236-bp sequence of the citrate synthase gene (gltA) of Anaplasma (Ehrlichia) platys were determined. The topology of the groEL- and gltA-based phylogenetic tree was similar to that derived from 16S rRNA gene analyses with distances. Both groESL- and gltA-based PCRs specific to A. platys were also developed based upon the alignment data.

The ascendancy of Amblyomma americanum as a vector of pathogens affecting humans in the United States

Until the 1990s, Amblyomma americanum was regarded primarily as a nuisance species, but a tick of minor importance as a vector of zoonotic pathogens affecting humans. With the recent discoveries of Ehrlichia chaffeensis, Ehrlichia ewingii, and "Borrelia lonestari," the public health relevance of lone star ticks is no longer in question. During the next 25 years, the number of cases of human disease caused by A. americanum-associated pathogens will probably increase. Based on current trajectories and historic precedents, the increase will be primarily driven by biological and environmental factors that alter the geographic distribution and intensity of transmission of zoonotic pathogens. Sociologic and demographic changes that influence the likelihood of highly susceptible humans coming into contact with infected lone star ticks, in addition to advances in diagnostic capabilities and national surveillance efforts, will also contribute to the anticipated increase in the number of recognized cases of disease.

Infections with Ehrlichia chaffeensis and Ehrlichia ewingii in persons coinfected with human immunodeficiency virus

The clinical course and laboratory evaluation of 21 patients coinfected with human immunodeficiency virus (HIV) and Ehrlichia chaffeensis or Ehrlichia ewingii are reviewed and summarized, including 13 cases of ehrlichiosis caused by E. chaffeensis, 4 caused by E. ewingii, and 4 caused by either E. chaffeensis or E. ewingii. Twenty patients were male, and the median CD4(+) T lymphocyte count was 137 cells/microL. Exposures to infecting ticks were linked to recreational pursuits, occupations, and peridomestic activities. For 8 patients, a diagnosis of ehrlichiosis was not considered until > or =4 days after presentation. Severe manifestations occurred more frequently among patients infected with E. chaffeensis than they did among patients infected with E. ewingii, and all 6 deaths were caused by E. chaffeensis. Ehrlichiosis may be a life-threatening illness in HIV-infected persons, and the influence of multiple factors, including recent changes in the epidemiology and medical management of HIV infection, may increase the frequency with which ehrlichioses occur in this patient cohort.

Identification of a p28 gene in Ehrlichia ewingii: evaluation of gene for use as a target for a species-specific PCR diagnostic assay

PCR was used to amplify a 537-bp region of an Ehrlichia ewingii gene encoding a homologue of the 28-kDa major antigenic protein (P28) of Ehrlichia chaffeensis. The E. ewingii p28 gene homologue was amplified from DNA extracted from whole blood obtained from four humans and one canine with confirmed cases of infection. Sequencing of the PCR products (505 bp) revealed a partial gene with homology to outer membrane protein genes from Ehrlichia and Cowdria spp.: p30 of Ehrlichia canis (< or =71.3%), p28 of E. chaffeensis (< or =68.3%), and map1 of Cowdria ruminantium (67.3%). The peptide sequence of the E. ewingii partial gene product was deduced (168 amino acids) and the antigenicity profile was analyzed, revealing a hydrophilic protein with < or =69.1% identity to P28 of E. chaffeensis, < or =67.3% identity to P30 of E. canis, and < or =63.1% identity to MAP1 of C. ruminantium. Primers were selected from the E. ewingii p28 sequence and used to develop a species-specific PCR diagnostic assay. The p28 PCR assay amplified the expected 215-bp product from DNA that was extracted from EDTA-treated blood from each of the confirmed E. ewingii infections that were available. The assay did not produce PCR products with DNA extracted from E. chaffeensis-, E. canis-, or E. phagocytophila-infected samples, confirming the specificity of the p28 assay for E. ewingii. The sensitivity of the E. ewingii-specific PCR assay was evaluated and determined to detect as few as 38 copies of the p28 gene.

Citrate synthase gene sequence: a new tool for phylogenetic analysis and identification of Ehrlichia

The sequence of the citrate synthase gene (gltA) of 13 ehrlichial species (Ehrlichia chaffeensis, Ehrlichia canis, Ehrlichia muris, an Ehrlichia species recently detected from Ixodes ovatus, Cowdria ruminantium, Ehrlichia phagocytophila, Ehrlichia equi, the human granulocytic ehrlichiosis [HGE] agent, Anaplasma marginale, Anaplasma centrale, Ehrlichia sennetsu, Ehrlichia risticii, and Neorickettsia helminthoeca) have been determined by degenerate PCR and the Genome Walker method. The ehrlichial gltA genes are 1,197 bp (E. sennetsu and E. risticii) to 1,254 bp (A. marginale and A. centrale) long, and GC contents of the gene vary from 30.5% (Ehrlichia sp. detected from I. ovatus) to 51.0% (A. centrale). The percent identities of the gltA nucleotide sequences among ehrlichial species were 49.7% (E. risticii versus A. centrale) to 99.8% (HGE agent versus E. equi). The percent identities of deduced amino acid sequences were 44.4% (E. sennetsu versus E. muris) to 99.5% (HGE agent versus E. equi), whereas the homology range of 16S rRNA genes was 83.5% (E. risticii versus the Ehrlichia sp. detected from I. ovatus) to 99.9% (HGE agent, E. equi, and E. phagocytophila). The architecture of the phylogenetic trees constructed by gltA nucleotide sequences or amino acid sequences was similar to that derived from the 16S rRNA gene sequences but showed more-significant bootstrap values. Based upon the alignment analysis of the ehrlichial gltA sequences, two sets of primers were designed to amplify tick-borne Ehrlichia and Neorickettsia genogroup Ehrlichia (N. helminthoeca, E. sennetsu, and E. risticii), respectively. Tick-borne Ehrlichia species were specifically identified by restriction fragment length polymorphism (RFLP) patterns of AcsI and XhoI with the exception of E. muris and the very closely related ehrlichia derived from I. ovatus for which sequence analysis of the PCR product is needed. Similarly, Neorickettsia genogroup Ehrlichia species were specifically identified by RFLP patterns of RcaI digestion. If confirmed this technique will be useful in rapidly identifying Ehrlichia spp.

Determination of Enterococcus faecalis groESL full-length sequence and application for species identification

Amplification of the partial Cpn60 (or GroEL) gene segment has been used for identification of many bacteria, including Enterococcus species. To obtain more sequence data from groESL genes of Enterococcus faecalis, the full-length sequence of the E. faecalis groESL genes containing groES (285 bp), spacer (57 bp), and groEL (1,626 bp) was determined. A database search of GenBank revealed that the deduced E. faecalis GroES and GroEL proteins show significant homology to the GroES and GroEL proteins of other bacteria. The GroEL (groEL) of E. faecalis had the highest identity with Streptococcus pneumoniae (81.8% amino acid sequence identity and 73.0% nucleotide sequence identity), followed by Lactococcus zeae, while GroES (groES) had 60.2% (64.6%) identity with Lactobacillus zeae and 58.5% (66.2%) identity with Lactococcus lactis, followed by 57.0% (65.5%) identity with Bacillus subtilis. Based on the groES sequence, an E. faecalis-specific PCR assay was developed, and this PCR assay was positive for all the E. faecalis strains tested. Dot blot hybridization using either groES or groEL as the probe distinguished E. faecalis clearly from other species, indicating that both genes can be used as suitable targets for E. faecalis identification. Moreover, broad-range PCR-restriction fragment length polymorphism of groESL was designed to differentiate eight commonly encountered Enterococcus species. The Enterococcus species of reference strains could be easily differentiated on the basis of restriction patterns produced by HaeIII and RsaI. The DNA-based assays developed in this study provide an alternative to currently used methods of identification for clinically important enterococcal species.