Transovarial transmission of Francisella-like endosymbionts and Anaplasma phagocytophilum variants in Dermacentor albipictus (Acari: Ixodidae)

Dermacentor albipictus (Packard) is a North American tick that feeds on cervids and livestock. It is a suspected vector of anaplasmosis in cattle, but its microbial flora and vector potential remain underevaluated. We screened D. albipictus ticks collected from Minnesota white-tailed deer (Odocoileus virginianus) for bacteria of the genera Anaplasma, Ehrlichia, Francisella, and Rickettsia using polymerase chain reaction (PCR) gene amplification and sequence analyses. We detected Anaplasma phagocytophilum and Francisella-like endosymbionts (FLEs) in nymphal and adult ticks of both sexes at 45 and 94% prevalences, respectively. The A. phagocytophilum and FLEs were transovarially transmitted to F1 larvae by individual ticks at efficiencies of 10-40 and 95-100%, respectively. The FLEs were transovarially transmitted to F2 larvae obtained as progeny of adults from F1 larval ticks reared to maturity on a calf, but A. phagocytophilum were not. Based on PCR and tissue culture inoculation assays, A. phagocytophilum and FLEs were not transmitted to the calf. The amplified FLE 16S rRNA gene sequences were identical to that of an FLE detected in a D. albipictus from Texas, whereas those of the A. phagocytophilum were nearly identical to those of probable human-nonpathogenic A. phagocytophilum WI-1 and WI-2 variants detected in white-tailed deer from central Wisconsin. However, the D. albipictus A. phagocytophilum sequences differed from that of the nonpathogenic A. phagocytophilum variant-1 associated with Ixodes scapularis ticks and white-tailed deer as well as that of the human-pathogenic A. phagocytophilum ha variant associated with I. scapularis and the white-footed mouse, Peromyscus leucopus. The transovarial transmission of A. phagocytophilum variants in Dermacentor ticks suggests that maintenance of A. phagocytophilum in nature may not be solely dependent on horizontal transmission.

Transgene expression and silencing in a tick cell line: A model system for functional tick genomics

The genome project of the black legged tick, Ixodes scapularis, provides sequence data for testing gene function and regulation in this important pathogen vector. We tested Sleeping Beauty (SB), a Tc1/mariner group transposable element, and cationic lipid-based transfection reagents for delivery and genomic integration of transgenes into I. scapularis cell line ISE6. Plasmid DNA and dsRNA were effectively transfected into ISE6 cells and they were successfully transformed to express a red fluorescent protein (DsRed2) and a selectable marker, neomycin phosphotransferase (NEO). Frequency of transformation was estimated as 1 transformant per 5000-10,000 cells and cultures were incubated for 2-3 months in medium containing the neomycin analog G418 in order to isolate transformants. Genomic integration of the DsRed2 transgene was confirmed by inverse PCR and sequencing that demonstrated a TA nucleotide pair inserted between SB inverted/direct repeat sequences and tick genomic sequences, indicating that insertion of the DsRed2 gene into the tick cell genome occurred through the activity of SB transposase. RNAi using dsRNA transcribed from the DsRed2 gene silenced expression of red fluorescent protein in transformed ISE6 cells. SB transposition in cell line ISE6 provides an effective means to explore the functional genomics of I. scapularis.

Intracellular infection of tick cell lines by the entomopathogenic fungus Metarhizium anisopliae

Several fungal pathogens are able to enter and persist within eukaryotic cells as part of their infectious life cycle. Metarhizium anisopliae is a saprophytic entomopathogenic fungus virulent towards numerous tick species, including those within the genera Ixodes and Amblyomma. Infection of the target organism by this fungus proceeds via several steps, including adhesion and penetration of the host cuticle, proliferation within tissues and the haemolymph, and eventual eruption through the host cadaver. To determine whether M. anisopliae could enter and persist within tick cells, we examined the uptake of wild-type and green fluorescent protein (GFP)-expressing fungal strains into two different tick cells lines, IDE12 and AAE2, derived from Ixodes scapularis and Amblyomma americanum, respectively. Uptake by tick cells was monitored by confocal fluorescent microscopy, as well as by scanning and transmission electron microscopy. M. anisopliae-specific antibodies were used to discriminate between extracellular and internalized fungal cells and to quantify the rate of uptake. Both cell lines internalized fungal conidia, and quantitative studies using the AAE2 cell line indicated that almost 70% of the AAE2 cells contained internalized conidia after 6 h incubation. Internalization of conidia by AAE2 cells was time and temperature dependent and could be inhibited by 80% with 1 mM cytochalasin D. Internalized conidia remained viable within the AAE2 cells, where they were able to germinate and grow, eventually erupting from the host cells. These data provide evidence that M. anisopliae conidia can be internalized, survive and grow within phagocytic cells in vitro and indicate that phagocytosis may serve as an alternative invasion route facilitating fungal nutrient acquisition, immune system evasion and dissemination throughout the host.

Whole genome transcription profiling of Anaplasma phagocytophilum in human and tick host cells by tiling array analysis

Background

Anaplasma phagocytophilum (Ap) is an obligate intracellular bacterium and the agent of human granulocytic anaplasmosis, an emerging tick-borne disease. Ap alternately infects ticks and mammals and a variety of cell types within each. Understanding the biology behind such versatile cellular parasitism may be derived through the use of tiling microarrays to establish high resolution, genome-wide transcription profiles of the organism as it infects cell lines representative of its life cycle (tick; ISE6) and pathogenesis (human; HL-60 and HMEC-1).

Results

Detailed, host cell specific transcriptional behavior was revealed. There was extensive differential Ap gene transcription between the tick (ISE6) and the human (HL-60 and HMEC-1) cell lines, with far fewer differentially transcribed genes between the human cell lines, and all disproportionately represented by membrane or surface proteins. There were Ap genes exclusively transcribed in each cell line, apparent human- and tick-specific operons and paralogs, and anti-sense transcripts that suggest novel expression regulation processes. Seven virB2 paralogs (of the bacterial type IV secretion system) showed human or tick cell dependent transcription. Previously unrecognized genes and coding sequences were identified, as were the expressed p44/msp2 (major surface proteins) paralogs (of 114 total), through elevated signal produced to the unique hypervariable region of each – 2/114 in HL-60, 3/114 in HMEC-1, and none in ISE6.

Conclusion

Using these methods, whole genome transcription profiles can likely be generated for Ap, as well as other obligate intracellular organisms, in any host cells and for all stages of the cell infection process. Visual representation of comprehensive transcription data alongside an annotated map of the genome renders complex transcription into discernable patterns.

Cellular and molecular characterization of an embryonic cell line (BME26) from the tick Rhipicephalus (Boophilus) microplus

The cellular and molecular characteristics of a cell line (BME26) derived from embryos of the cattle tick Rhipicephalus (Boophilus) microplus were studied. The cells contained glycogen inclusions, numerous mitochondria, and vesicles with heterogeneous electron densities dispersed throughout the cytoplasm. Vesicles contained lipids and sequestered palladium meso-porphyrin (Pd-mP) and rhodamine-hemoglobin, suggesting their involvement in the autophagic and endocytic pathways. The cells phagocytosed yeast and expressed genes encoding the antimicrobial peptides (microplusin and defensin). A cDNA library was made and 898 unique mRNA sequences were obtained. Among them, 556 sequences were not significantly similar to any sequence found in public databases. Annotation using Gene Ontology revealed transcripts related to several different functional classes. We identified transcripts involved in immune response such as ferritin, serine proteases, protease inhibitors, antimicrobial peptides, heat shock protein, glutathione S-transferase, peroxidase, and NADPH oxidase. BME26 cells transfected with a plasmid carrying a red fluorescent protein reporter gene (DsRed2) transiently expressed DsRed2 for up to 5 weeks. We conclude that BME26 can be used to experimentally analyze diverse biological processes that occur in R. (B.) microplus such as the innate immune response to tick-borne pathogens.

Isolation of cell lines and a rickettsial endosymbiont from the soft tick Carios capensis (Acari: Argasidae: Ornithodorinae)

Soft ticks are medically important ectoparasites of birds and mammals that are found throughout the world. This report describes isolation and partial characterization of two embryonic cell lines, CCE2 and CCE3, from the seabird soft tick Carios capensis (Neumann). Sequencing of the mitochondrial 16S rRNA gene and karyology confirmed the lines were derived from C. capensis. CCE3 cells were diploid with a modal chromosome number of 20. The population doubling time for cell lines CCE2 and 3 in passage 40 was 6-9 d. A rickettsial endosymbiont, RCCE3, was co-isolated along with line CCE3. Nucleotide sequences of polymerase chain reaction (PCR) products generated using primers specific for rickettsial 17-kDa antigen, outer membrane protein (omp) A, ompB, and citrate synthase genes along with phylogenetic analyses demonstrated that RCCE3 is a previously uncultured endosymbiont. The rickettsia was identified as a symbiont of C. capensis, closely related to rickettsiae previously detected by PCR in C. capensis, Ornithodoros moubata (Murray) and Hemaphysalis sulcata Canestrini & Fanzago, a hard tick. RCCE3 caused a cytopathic effect in C. capensis host cells, and it was transferred to Ixodes scapularis Say cell line ISE6 for maintenance. The rickettsial endosymbiont was eliminated from CCE3 by treatment with oxytetracycline. Cell lines from C. capensis will be useful to researchers investigating interactions between soft ticks and microorganisms, soft tick physiology, and molecular biology. The rickettsia adds to the growing number of Rickettsia species that have been isolated in tick cell culture, and it is available for characterization.

Transposon insertion reveals pRM, a plasmid of Rickettsia monacensis

Until the recent discovery of pRF in Rickettsia felis, the obligate intracellular bacteria of the genus Rickettsia (Rickettsiales: Rickettsiaceae) were thought not to possess plasmids. We describe pRM, a plasmid from Rickettsia monacensis, which was detected by pulsed-field gel electrophoresis and Southern blot analyses of DNA from two independent R. monacensis populations transformed by transposon-mediated insertion of coupled green fluorescent protein and chloramphenicol acetyltransferase marker genes into pRM. Two-dimensional electrophoresis showed that pRM was present in rickettsial cells as circular and linear isomers. The 23,486-nucleotide (31.8% G/C) pRM plasmid was cloned from the transformant populations by chloramphenicol marker rescue of restriction enzyme-digested transformant DNA fragments and PCR using primers derived from sequences of overlapping restriction fragments. The plasmid was sequenced. Based on BLAST searches of the GenBank database, pRM contained 23 predicted genes or pseudogenes and was remarkably similar to the larger pRF plasmid. Two of the 23 genes were unique to pRM and pRF among sequenced rickettsial genomes, and 4 of the genes shared by pRM and pRF were otherwise found only on chromosomes of R. felis or the ancestral group rickettsiae R. bellii and R. canadensis. We obtained pulsed-field gel electrophoresis and Southern blot evidence for a plasmid in R. amblyommii isolate WB-8-2 that contained genes conserved between pRM and pRF. The pRM plasmid may provide a basis for the development of a rickettsial transformation vector.

Isolation and propagation of the Ap-Variant 1 strain of Anaplasma phagocytophilum in a tick cell line

The first tissue culture isolates of the unique Anaplasma phagocytophilum strain, Ap-Variant 1, were obtained in the Ixodes scapularis tick-derived cell line ISE6. Two isolates were from goat blood samples: one from a goat infected with I. scapularis ticks from Rhode Island and a second from a goat infected by serial passage of blood from the first infected goat. Eight isolates were made directly from I. scapularis ticks collected from white-tailed deer in Minnesota and represent the first isolations of an Anaplasma species directly from ticks. Each of the 10 isolates had a 16S rRNA gene sequence identical to that previously described for Ap-Variant 1, but differences within the ank gene were found that suggest natural variation. Prevalence of Anaplasma in the Minnesota ticks was 63.9%; 23 of 36 ticks tested by PCR were positive. Six of the tick-derived isolates were obtained from a set of 18 PCR-positive ticks, for a 33.3% isolation success rate. The conservation of host tropism among the Rhode Island and Minnesota isolates of Ap-Variant 1 was examined by use of experimental infections of mice and a goat. A Minnesota tick-derived isolate (MN-61-2) was used to inoculate naïve animals, and this isolate was able to infect a goat but unable to infect each of five mice, confirming that the Minnesota isolates have the same host tropism as Ap-Variant 1 from the northeastern United States. Light and electron microscopy of the Ap-Variant 1 isolate MN-61-2 in ISE6 cells showed cytoplasmic inclusions characteristic of A. phagocytophilum with pleomorphic bacteria in membrane-bound vacuoles and both electron-dense and electron-lucent forms.

Isolation of Anaplasma phagocytophilum strain Ap-variant 1 in a tick-derived cell line

Ten isolates of the Ap-Variant 1 strain of Anaplasma phagocytophilum were made in the Ixodes scapularis (I. scapularis)-derived cell line, ISE6. Two isolates were obtained from laboratory-infected goats and eight isolates were obtained from field-collected I. scapularis ticks. Each isolate showed 16S rRNA sequences identical to those as previously described for the Ap-Variant 1 strain. These are the first tissue culture isolates of the Ap-Variant 1 strain and will allow for further characterization of the biological and antigenic properties of this strain.

Rickettsia peacockii, an endosymbiont of Dermacentor andersoni, does not elicit or inhibit humoral immune responses from immunocompetent D. andersoni or Ixodes scapularis cell lines

Ixodes scapularis and Dermacentor andersoni cell lines were stimulated with heat-killed Escherichia coli and Micrococcus luteus to investigate whether infection by Rickettsia peacockii, an endosymbiont of D. andersoni, modifies humoral immune responses. Radial diffusion assays, western blotting, flow cytometry, and quantitative reverse-transcription PCR were used to determine if expression of bacteriolytic peptides, including lysozyme and defensin, was upregulated by bacterial stimulation or infection with R. peacockii. The I. scapularis line IDE12 upregulated expression of lysozyme and defensin following stimulation. The D. andersoni cell line DAE15 also expressed defensin and lysozyme, but only lysozyme was upregulated by bacterial stimulation. R. peacockii infection alone, or in cells stimulated with bacteria, did not modify defensin or lysozyme expression in either cell line. These results suggest tick endosymbionts may avoid recognition by the tick immune system, and infection may not affect humoral immune responses to bacteria not normally associated with ticks.

Phagocytosis of the Lyme disease spirochete, Borrelia burgdorferi, by cells from the ticks, Ixodes scapularis and Dermacentor andersoni, infected with an endosymbiont, Rickettsia peacockii

Tick cell lines were used to model the effects of endosymbiont infection on phagocytic immune responses. The lines tested for their ability to phagocytose the Lyme disease spirochete, Borrelia burgdorferi (Spirochaetales: Spirochaetaceae), were ISE6 and IDE12 from the black-legged tick, Ixodes scapularis Say (Acari: Ixodidae) and DAE15 from the Rocky Mountain wood tick, Dermacentor andersoni Stiles. Rickettsia peacockii (Rickettsiales: Rickettsiaceae), an endosymbiont of D. andersoni, was used as a representative tick endosymbiont. 70-80% of uninfected or R. peacocciz-infected IDE12 and DAE15 cells phagocytosed heat-killed borreliae and 80-90% of IDE12 and DAE15 cells phagocytosed viable spirochetes. ISE6 cells were permissive of spirochetes; less than 1% of these cells phagocytosed borreliae, and spirochetes remained adherent to the cells seven days after inoculation. Cytochalasin B blocked phagocytosis of killed and viable borreliae by IDE12 cells, and prevented phagocytosis of killed spirochetes by DAE15 cells, whereas viable spirochetes successfully invaded cytochalasin-treated DAE15. IDE12 and DAE15 cells degraded borreliae within phagolysosome-like compartments. Time-lapse microscopy showed that DAE15 cells phagocytosed borreliae more rapidly than IDE12 cells. IDE12 and DAE15 cells eliminated most adherent spirochetes within 7 days of inoculation. Thus, endosymbiont infection does not significantly interfere with the phagocytic activity of immunocompetent tick cells.

Infection of Ixodes scapularis ticks with Rickettsia monacensis expressing green fluorescent protein: a model system

Ticks (Acari: Ixodidae) are ubiquitous hosts of rickettsiae (Rickettsiaceae: Rickettsia), obligate intracellular bacteria that occur as a continuum from nonpathogenic arthropod endosymbionts to virulent pathogens of both arthropod vectors and vertebrates. Visualization of rickettsiae in hosts has traditionally been limited to techniques utilizing fixed tissues. We report epifluorescence microscopy observations of unfixed tick tissues infected with a spotted fever group endosymbiont, Rickettsia monacensis, transformed to express green fluorescent protein (GFP). Fluorescent rickettsiae were readily visualized in tick tissues. In adult female, but not male, Ixodes scapularis infected by capillary feeding, R. monacensis disseminated from the gut and infected the salivary glands that are crucial to the role of ticks as vectors. The rickettsiae infected the respiratory tracheal system, a potential dissemination pathway and possible infection reservoir during tick molting. R. monacensis disseminated from the gut of capillary fed I. scapularis nymphs and was transstadially transmitted to adults. Larvae, infected by immersion, transstadially transmitted the rickettsiae to nymphs. Infected female I. scapularis did not transovarially transmit R. monacensis to progeny and the rickettsiae were not horizontally transmitted to a rabbit or hamsters. Survival of infected nymphal and adult I. scapularis did not differ from that of uninfected control ticks. R. monacensis did not disseminate from the gut of capillary fed adult female Amblyomma americanum (L.), or adult Dermacentor variabilis (Say) ticks of either sex. Infection of I. scapularis with R. monacensis expressing GFP provides a model system allowing visualization and study of live rickettsiae in unfixed tissues of an arthropod host.

Transformation of Anaplasma phagocytophilum

Background

Tick-borne pathogens cause emerging zoonoses, and include fastidious organisms such as Anaplasma phagocytophilum. Because of their obligate intracellular nature, methods for mutagenesis and transformation have not been available.

Results

To facilitate genetic manipulation, we transformed A. phagocytophilum (Ap) to express a green fluorescent protein (GFP) with the Himar1 transposase system and selection with the clinically irrelevant antibiotic spectinomycin.

Conclusion

These transformed bacteria (GFP/Ap) grow at normal rates and are brightly fluorescent in human, monkey, and tick cell culture. Molecular characterization of the GFP/Ap genomic DNA confirmed transposition and the flanking genomic insertion locations were sequenced. Three mice inoculated with GFP/Ap by intraperitoneal injection became infected as demonstrated by the appearance of morulae in a peripheral blood neutrophil and re-isolation of the bacteria in culture.

Characterization of a new densovirus infecting the German cockroach, Blattella germanica

A new DNA virus (Parvoviridae: Densovirinae, Densovirus) was isolated and purified from descendants of field-collected German cockroaches, Blattella germanica. Viral DNA and cockroach tissues infected with B. germanica densovirus (BgDNV) were examined by electron microscopy. Virus particles, about 20 nm in diameter, were observed both in the nucleus and in the cytoplasm of infected cells. Virus DNA proved to be a linear molecule of about 1.2 microm in length. BgDNV isolated from infected cockroaches infected successfully and could be maintained in BGE-2, a B. germanica cell line. The complete BgDNV genome was sequenced and analysed. Five open reading frames (ORFs) were detected in the 5335 nt sequence: two ORFS that were on one DNA strand encoded structural capsid proteins (69.7 and 24.8 kDa) and three ORFs that were on the other strand encoded non-structural proteins (60.2, 30.3 and 25.9 kDa). Three putative promoters and polyadenylation signals were identified. Structural analysis of the inverted terminal repeats revealed the presence of extended palindromes. The genome structure of BgDNV was compared with that of other members of the family Parvoviridae; the predicted amino acid sequences were aligned and subjected to phylogenetic analyses.

In vitro cultivation and antibiotic susceptibility of a Cytophaga-like intracellular symbiote isolated from the tick Ixodes scapularis

A Cytophaga-like organism (CLO), isolated from the tick Ixodes scapularis (IsCLO), was adapted to growth in insect cell lines and its antibiotic sensitivity was tested. IsCLO were introduced to four insect cell lines, and their growth was measured by quantitative polymerase chain reaction. IsCLO propagated well in a mosquito cell line, AeAl-2, and caused cytopathic effects in host cells. A lepidopteran cell line, HZ-AM1, was also suitable for propagation of IsCLO and kept a steady state with bacterial growth. Using IsCLO-infected AeAl-2, antibiotics effective against the bacteria included ampicillin, chloramphenicol, penicillin-G, rifampicin, and tetracycline. These antibiotics will be useful for eliminating CLO from host arthropods, which is necessary for in vivo studies of the intracellular facultative symbiotes.

The Interactions of Anaplasma phagocytophilum, Endothelial Cells, and Human Neutrophils

Ixodes scapularis ticks transmit Anaplasma phagocytophilum (Ap), agent of human granulocytic anaplasmosis (HGA). Invasion of neutrophil granulocytes (PMN) by Ap is the hallmark of the disease, but these short-lived phagocytes are not likely the sole cell type required for productive infection. We analyzed infection of microvascular endothelial cells during pathogenesis of anaplasmosis in vivo and in vitro. Organs from Ap-infected mice were processed for confocal microscopy 41 days p.i. Fluorescent labeling of heart and liver sections using anti-factor VIII and anti-MSP2 antibodies allowed colocalization of Ap and vascular endothelium, indicating infection. Ap rapidly invaded and grew within HMEC-1 human microvascular endothelial cells and readily transferred to PMN. Over 50% of PMN became infected within two hours of coincubation with HMEC-1. PMN adhered to, polarized, and migrated upon infected endothelial monolayers. The Ap receptor on human PMN is PSGL-1, and infected endothelial cells upregulate ICAM-1 (CD54), but the mechanisms of transfer of Ap remain unknown. To elucidate the cellular determinants involved, we tested relevant antibodies and lectins. Anti-PSGL-1 reduced infection of PMN, but did not inhibit adherence of PMN to Ap infected HMEC-1 cells while anti-CD18 did. Sialidase pretreatment increased, and EDTA and fucoidan decreased binding of Ap to HMEC-1, whereas several other lectins had no effect. An endothelial reservoir of Ap offers opportunities for ongoing, direct cell-to-cell infection of PMN, avoidance of host immune effectors, and completion of the Ap life cycle by infection of circulating leukocytes available for transfer to blood-feeding ticks.

Factors influencing in vitro infectivity and growth of Rickettsia peacockii (Rickettsiales: Rickettsiaceae), an endosymbiont of the Rocky Mountain wood tick, Dermacentor andersoni (Acari, Ixodidae)

Rickettsia peacockii, a spotted fever group rickettsia, is a transovarially transmitted endosymbiont of Rocky Mountain wood ticks, Dermacentor andersoni. This rickettsia, formerly known as the East Side Agent and restricted to female ticks, was detected in a chronically infected embryonic cell line, DAE100, from D. andersoni. We examined infectivity, ability to induce cytopathic effect (CPE) and host cell specificity of R. peacockii using cultured arthropod and mammalian cells. Aposymbiotic DAE100 cells were obtained using oxytetracycline or incubation at 37 degrees C. Uninfected DAE100 sublines grew faster than the parent line, indicating R. peacockii regulation of host cell growth. Nevertheless, DAE100 cellular defenses exerted partial control over R. peacockii growth. Rickettsiae existed free in the cytosol of DAE100 cells or within autophagolysosomes. Exocytosed rickettsiae accumulated in the medium and were occasionally contained within host membranes. R. peacockii multiplied in other cell lines from the hard ticks D. andersoni, Dermacentor albipictus, Ixodes scapularis, and Ixodes ricinus; the soft tick Carios capensis; and the lepidopteran Trichoplusia ni. Lines from the tick Amblyomma americanum, the mosquito Aedes albopictus, and two mammalian cell lines were non-permissive to R. peacockii. High cell densities facilitated rickettsial spread within permissive cell cultures, and an inoculum of one infected to nine uninfected cells resulted in the greatest yield of infected tick cells. Cell-free R. peacockii also were infectious for tick cells and centrifugation onto cell layers enhanced infectivity approximately 100-fold. The ability of R. peacockii to cause mild CPE suggests that its pathogenicity is not completely muted. An analysis of R. peacockii-cell interactions in comparison to pathogenic rickettsiae will provide insights into host cell colonization mechanisms.

Susceptibility of Rickettsia monacensis and Rickettsia peacockii to Cecropin A, Ceratotoxin A, and Lysozyme

Ticks host obligate intracellular bacteria that range from benign symbiotes to virulent human pathogens. The effects on those bacteria of antimicrobial peptides (AMPs) involved in arthropod innate immunity to microbial infections are largely unknown. We evaluated effects of AMPs and a c-type lysozyme on host cell-free suspensions of the tick symbiotes Rickettsia monacensis and Rickettsia peacockii with stain-based infectivity and viability assays. Cecropin A at a concentration of 8 muM: had a lethal effect on both rickettsiae while ceratotoxin A was approximately 20-fold less effective. Toxicity of both AMPs was synergized by lysozyme, an enzyme expressed by ticks. Lactoferrin, a transferrin, had no effect on R. monacensis at up to 110 microM. The rickettsiae were less sensitive to the AMPs than is typical of bacteria that grow extracellularly. Our assays may be useful in the study of AMP activity against other obligate intracellular bacteria.

Analysis of fluorescent protein expression in transformants of Rickettsia monacensis, an obligate intracellular tick symbiont

We developed and applied transposon-based transformation vectors for molecular manipulation and analysis of spotted fever group rickettsiae, which are obligate intracellular bacteria that infect ticks and, in some cases, mammals. Using the Epicentre EZ::TN transposon system, we designed transposons for simultaneous expression of a reporter gene and a chloramphenicol acetyltransferase (CAT) resistance marker. Transposomes (transposon-transposase complexes) were electroporated into Rickettsia monacensis, a rickettsial symbiont isolated from the tick Ixodes ricinus. Each transposon contained an expression cassette consisting of the rickettsial ompA promoter and a green fluorescent protein (GFP) reporter gene (GFPuv) or the ompB promoter and a red fluorescent protein reporter gene (DsRed2), followed by the ompA transcription terminator and a second ompA promoter CAT gene cassette. Selection with chloramphenicol gave rise to rickettsial populations with chromosomally integrated single-copy transposons as determined by PCR, Southern blotting, and sequence analysis. Reverse transcription-PCR and Northern blots demonstrated transcription of all three genes. GFPuv transformant rickettsiae exhibited strong fluorescence in individual cells, but DsRed2 transformants did not. Western blots confirmed expression of GFPuv in R. monacensis and in Escherichia coli, but DsRed2 was expressed only in E. coli. The DsRed2 gene, but not the GFPuv gene, contains many GC-rich amino acid codons that are rare in the preferred codon suite of rickettsiae, possibly explaining the failure to express DsRed2 protein in R. monacensis. We demonstrated that our vectors provide a means to study rickettsia-host cell interactions by visualizing GFPuv-fluorescent R. monacensis associated with actin tails in tick host cells.

Sequence and expression analysis of the ompA gene of Rickettsia peacockii, an endosymbiont of the Rocky Mountain wood tick, Dermacentor andersoni

The transmission dynamics of Rocky Mountain spotted fever in Montana appears to be regulated by Rickettsia peacockii, a tick symbiotic rickettsia that interferes with transmission of virulent Rickettsia rickettsii. To elucidate the molecular relationships between the two rickettsiae and glean information on how to possibly exploit this interference phenomenon, we studied a major rickettsial outer membrane protein gene, ompA, presumed to be involved in infection and pathogenesis of spotted fever group rickettsiae (SFGR) but which is not expressed in the symbiont. Based on PCR amplification and DNA sequence analysis of the SFGR ompA gene, we demonstrate that R. peacockii is the most closely related of all known SFGR to R. rickettsii. We show that R. peacockii, originally described as East Side agent in Dermacentor andersoni ticks from the east side of the Bitterroot Valley in Montana, is still present in that tick population as well as in D. andersoni ticks collected at two widely separated locations in Colorado. The ompA genes of R. peacockii from these locations share three identical premature stop codons and a weakened ribosome binding site consensus sequence relative to ompA of R. rickettsii. The R. peacockii ompA promoter closely resembles that of R. rickettsii and is functional based on reverse transcription-PCR results. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting showed that OmpA translation products were not detected in cultured tick cells infected with R. peacockii. Double immunolabeling studies revealed actin tail structures in tick cells infected with R. rickettsii strain Hlp#2 but not in cells infected with R. peacockii.

Infection of endothelial cells with Anaplasma marginale and A. phagocytophilum

Anaplasma marginale and A. phagocytophilum are obligate intracellular, tick-borne pathogens that target erythrocytes and neutrophil granulocytes, respectively. Because ticks do not directly tap blood vessels, an intermediate tissue may mediate infection of blood cells. We considered that vascular endothelium interacts with circulating blood cells in vivo, and could be involved in pathogenesis and dissemination of the organisms. We used light and electron microscopy and immune labeling to show that A. phagocytophilum invaded rhesus (RF/6A), human (HMEC-1, MVEC), as well as bovine (BCE C/D-1b) endothelial cell lines, whereas A. marginale infected rhesus and bovine endothelial cells. A. marginale formed large intracellular inclusions that appeared smooth and solid at first, and subsequently coalesced into discrete granules. A. phagocytophilum formed numerous smaller inclusions in each cell. Within 1-3 weeks, the monolayers were destroyed, and lysed cultures were diluted onto fresh monolayers. Electron microscopy demonstrated uneven distribution of A. marginale inside large inclusions, with reticulated forms grouped more tightly than denser cells, whereas in A. phagocytophilum individual organisms appeared more evenly spaced. Specific polyclonal and monoclonal antibodies both labeled A. marginale and A. phagocytophilum in endothelial cells, and oligonucleotide primers complimentary to either A. marginale or A. phagocytophilum amplified their expected target from these cultures. In conclusion, we demonstrate that relevant microvascular endothelium is susceptible to anaplasmas in vitro and may present a link that could explain development of the immune response and persistent infection.

Experimental infection of dogs with Borrelia burgdorferi sensu stricto using Ixodes scapularis ticks artificially infected by capillary feeding

Specific pathogen-free dogs were experimentally infected with Borrelia burgdorferi sensu stricto using nymphal or adult female Ixodes scapularis ticks artificially infected with spirochetes by capillary feeding. The ticks were capillary fed B. burgdorferi isolate 610, previously isolated from a dog with Lyme disease and grown in BSK medium. This isolate induced clinical signs in the dogs similar to those for dogs infested with ticks naturally infected with B. burgdorferi. Adult ticks were more efficient than nymphs in transmitting spirochetes to the dogs. One of five dogs infested with nymphal ticks capillary fed B. burgdorferi was skin biopsy culture and serologically positive, and demonstrated lameness. In contrast, all five dogs infested with adult female ticks that had been capillary fed with B. burgdorferi were culture and serologically positive, with one dog developing lameness. The immunoblot profiles of dogs challenged with female ticks infected by capillary feeding (8 weeks post challenge) were similar to immunoblots (4 weeks post challenge) from dogs challenged with naturally infected females collected in the field. These studies demonstrated that B. burgdorferi cultured in BSK medium can be capillary fed to either nymphal or adult female ticks under laboratory controlled conditions for the purpose of transmitting the spirochete to dogs during the tick's blood meal. This tick infection system would be useful for a controlled and defined challenge of vaccinated and non-vaccinated dogs for proper evaluation of vaccine efficacy, which is difficult to achieve using field-collected ticks. Furthermore, this system may also be useful for investigation of the pathogenesis of Lyme disease, evaluation of the pathogenicity of new isolates of B. burgdorferi, or evaluation of antibiotic therapy.

Isolation of an Anaplasma sp. organism from white-tailed deer by tick cell culture

We used tick cell culture to isolate a bacterium previously referred to as the "white-tailed deer (WTD) agent" from two captive fawns inoculated with blood from wild WTD (Odocoileus virginianus). Buffy coat cells were added to ISE6 tick cell cultures and incubated at 34 degrees C, and 8 days later, Anaplasma-like inclusions were demonstrated in Giemsa-stained culture samples. The microbes became established and could be continuously passaged in tick cells. The identity of a culture isolate designated WTD76 was verified as the WTD agent by using specific PCR primers and by DNA sequencing. Comparison with sequences available in GenBank indicated that the isolate was most closely related first to Anaplasma platys and second to Anaplasma phagocytophilum, supporting its placement in the genus Anaplasma. Transmission electron microscopy of this Anaplasma sp. organism in tick cell cultures revealed large inclusions filled with pleomorphic and rod-shaped bacteria. Tick cells infected with the Anaplasma sp. organism were used to successfully infect a naive deer, thereby proving the infectivity of the isolate for deer.

Rickettsia monacensis sp. nov., a spotted fever group Rickettsia, from ticks (Ixodes ricinus) collected in a European city park

We describe the isolation and characterization of Rickettsia monacensis sp. nov. (type strain, IrR/Munich(T)) from an Ixodes ricinus tick collected in a city park, the English Garden in Munich, Germany. Rickettsiae were propagated in vitro with Ixodes scapularis cell line ISE6. BLAST analysis of the 16S rRNA, the citrate synthase, and the partial 190-kDa rickettsial outer membrane protein A (rOmpA) gene sequences demonstrated that the isolate was a spotted fever group (SFG) rickettsia closely related to several yet-to-be-cultivated rickettsiae associated with I. ricinus. Phylogenetic analysis of partial rompA sequences demonstrated that the isolate was genotypically different from other validated species of SFG rickettsiae. R. monacensis also replicated in cell lines derived from the ticks I. ricinus (IRE11) and Dermacentor andersoni (DAE100) and in the mammalian cell lines L-929 and Vero, causing cell lysis. Transmission electron microscopy of infected ISE6 and Vero cells showed rickettsiae within the cytoplasm, pseudopodia, nuclei, and vacuoles. Hamsters inoculated with R. monacensis had immunoglobulin G antibody titers as high as 1:16,384, as determined by indirect immunofluorescence assay. Western blot analyses demonstrated that the hamster sera cross-reacted with peptides from other phylogenetically distinct rickettsiae, including rOmpA. R. monacensis induced actin tails in both tick and mammalian cells similar to those reported for R. rickettsii. R. monacensis joins a growing list of SFG rickettsiae that colonize ticks but whose infectivity and pathogenicity for vertebrates are unknown.