Molecular typing of Borrelia burgdorferi from Lyme disease patients by PCR-restriction fragment length polymorphism analysis

Whole genome sequencing of human Borrelia burgdorferi isolates reveals linked blocks of accessory genome elements located on plasmids and associated with human dissemination

Lyme disease is the most common vector-borne disease in North America and Europe. The clinical manifestations of Lyme disease vary based on the genospecies of the infecting Borrelia burgdorferi spirochete, but the microbial genetic elements underlying these associations are not known. Here, we report the whole genome sequence (WGS) and analysis of 299 B. burgdorferi (Bb) isolates derived from patients in the Eastern and Midwestern US and Central Europe. We develop a WGS-based classification of Bb isolates, confirm and extend the findings of previous single- and multi-locus typing systems, define the plasmid profiles of human-infectious Bb isolates, annotate the core and strain-variable surface lipoproteome, and identify loci associated with disseminated infection. A core genome consisting of ~900 open reading frames and a core set of plasmids consisting of lp17, lp25, lp36, lp28-3, lp28-4, lp54, and cp26 are found in nearly all isolates. Strain-variable (accessory) plasmids and genes correlate strongly with phylogeny. Using genetic association study methods, we identify an accessory genome signature associated with dissemination in humans and define the individual plasmids and genes that make up this signature. Strains within the RST1/WGS A subgroup, particularly a subset marked by the OspC type A genotype, have increased rates of dissemination in humans. OspC type A strains possess a unique set of strongly linked genetic elements including the presence of lp56 and lp28-1 plasmids and a cluster of genes that may contribute to their enhanced virulence compared to other genotypes. These features of OspC type A strains reflect a broader paradigm across Bb isolates, in which near-clonal genotypes are defined by strain-specific clusters of linked genetic elements, particularly those encoding surface-exposed lipoproteins. These clusters of genes are maintained by strain-specific patterns of plasmid occupancy and are associated with the probability of invasive infection.

Whole genome sequencing of Borrelia burgdorferi isolates reveals linked clusters of plasmid-borne accessory genome elements associated with virulence

Lyme disease is the most common vector-borne disease in North America and Europe. The clinical manifestations of Lyme disease vary based on the genospecies of the infecting Borrelia burgdorferi spirochete, but the microbial genetic elements underlying these associations are not known. Here, we report the whole genome sequence (WGS) and analysis of 299 patient-derived B. burgdorferi sensu stricto ( Bbss ) isolates from patients in the Eastern and Midwestern US and Central Europe. We develop a WGS-based classification of Bbss isolates, confirm and extend the findings of previous single- and multi-locus typing systems, define the plasmid profiles of human-infectious Bbss isolates, annotate the core and strain-variable surface lipoproteome, and identify loci associated with disseminated infection. A core genome consisting of ∼800 open reading frames and a core set of plasmids consisting of lp17, lp25, lp36, lp28-3, lp28-4, lp54, and cp26 are found in nearly all isolates. Strain-variable (accessory) plasmids and genes correlate strongly with phylogeny. Using genetic association study methods, we identify an accessory genome signature associated with dissemination and define the individual plasmids and genes that make up this signature. Strains within the RST1/WGS A subgroup, particularly a subset marked by the OspC type A genotype, are associated with increased rates of dissemination. OspC type A strains possess a unique constellation of strongly linked genetic changes including the presence of lp56 and lp28-1 plasmids and a cluster of genes that may contribute to their enhanced virulence compared to other genotypes. The patterns of OspC type A strains typify a broader paradigm across Bbss isolates, in which genetic structure is defined by correlated groups of strain-variable genes located predominantly on plasmids, particularly for expression of surface-exposed lipoproteins. These clusters of genes are inherited in blocks through strain-specific patterns of plasmid occupancy and are associated with the probability of invasive infection.

Testing Raman spectroscopy as a diagnostic approach for Lyme disease patients

Lyme disease (LD), the leading tick-borne disease in the Northern hemisphere, is caused by spirochetes of several genospecies of the Borreliella burgdorferi sensu lato complex. LD is a multi-systemic and highly debilitating illness that is notoriously challenging to diagnose. The main drawbacks of the two-tiered serology, the only approved diagnostic test in the United States, include poor sensitivity, background seropositivity, and cross-reactivity. Recently, Raman spectroscopy (RS) was examined for its LD diagnostic utility by our earlier proof-of-concept study. The previous investigation analyzed the blood from mice that were infected with 297 and B31 strains of Borreliella burgdorferi sensu stricto (s.s.). The selected strains represented two out of the three major clades of B. burgdorferi s.s. isolates found in the United States. The obtained results were encouraging and prompted us to further investigate the RS diagnostic capacity for LD in this study. The present investigation has analyzed blood of mice infected with European genospecies, Borreliella afzelii or Borreliella garinii, or B. burgdorferi N40, a strain of the third major class of B. burgdorferi s.s. in the United States. Moreover, 90 human serum samples that originated from LD-confirmed, LD-negative, and LD-probable human patients were also analyzed by RS. The overall results demonstrated that blood samples from Borreliella-infected mice were identified with 96% accuracy, 94% sensitivity, and 100% specificity. Furthermore, human blood samples were analyzed with 88% accuracy, 85% sensitivity, and 90% specificity. Together, the current data indicate that RS should be further explored as a potential diagnostic test for LD patients.

Borreliella burgdorferi Antimicrobial-Tolerant Persistence in Lyme Disease and Posttreatment Lyme Disease Syndromes

The annual incidence of Lyme disease, caused by tick-transmitted Borreliella burgdorferi, is estimated to be at least 476,000 cases in the United States and many more worldwide. Ten to 20% of antimicrobial-treated Lyme disease patients display posttreatment Lyme disease syndrome (PTLDS), a clinical complication whose etiology and pathogenesis remain uncertain. Autoimmunity, cross-reactivity, molecular mimicry, coinfections, and borrelial tolerance to antimicrobials/persistence have been hypothesized and studied as potential causes of PTLDS. Studies of borrelial tolerance/persistence in vitro in response to antimicrobials and experimental studies in mice and nonhuman primates, taken together with clinical reports, have revealed that B. burgdorferi becomes tolerant to antimicrobials and may sometimes persist in animals and humans after the currently recommended antimicrobial treatment. Moreover, B. burgdorferi is pleomorphic and can generate viable-but-nonculturable bacteria, states also involved in antimicrobial tolerance. The multiple regulatory pathways and structural genes involved in mediating this tolerance to antimicrobials and environmental stressors by persistence might include the stringent (rel and dksA) and host adaptation (rpoS) responses, sugar metabolism (glpD), and polypeptide transporters (opp). Application of this recently reported knowledge to clinical studies can be expected to clarify the potential role of bacterial antibacterial tolerance/persistence in Lyme disease and PTLDS.

Coinfection of Ixodes scapularis (Acari: Ixodidae) Nymphs With Babesia spp. (Piroplasmida: Babesiidae) and Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) in Wisconsin

Borrelia burgdorferi, the spirochete that causes Lyme disease, is endemic and widespread in Wisconsin. Research in the northeastern United States has revealed a positive association between Babesia microti, the main pathogen that causes babesiosis in humans, and Bo. burgdorferi in humans and in ticks. This study was conducted to examine associations between the disease agents in the Upper midwestern United States. Ixodes scapularis Say nymphs (N = 2,858) collected between 2015 and 2017 from nine locations in Wisconsin were tested for Babesia spp. and Borrelia spp. using real-time PCR. Two species of Babesia were detected; Ba. microti and Babesia odocoilei (a parasite of members of the family Cervidae). Prevalence of infection at the nine locations ranged from 0 to 13% for Ba. microti, 11 to 31% for Bo. burgdorferi sensu stricto, and 5.7 to 26% for Ba. odocoilei. Coinfection of nymphs with Bo. burgdorferi and Ba. odocoilei was detected in eight of the nine locations and significant positive associations were observed in two of the eight locations. The prevalence of nymphal coinfection with both and Bo. burgdorferi and Ba. microti ranged from 0.81 to 6.5%. These two pathogens were significantly positively associated in one of the five locations where both pathogens were detected. In the other four locations, the observed prevalence of coinfection was higher than expected in all but one site-year. Clinics and healthcare providers should be aware of the association between Ba. microti and Bo. burgdorferi pathogens when treating patients who report tick bites.

Lyme Neuroborreliosis: Mechanisms of B. burgdorferi Infection of the Nervous System

Lyme borreliosis is the most prevalent tick-borne disease in the United States, infecting ~476,000 people annually. Borrelia spp. spirochetal bacteria are the causative agents of Lyme disease in humans and are transmitted by Ixodes spp ticks. Clinical manifestations vary depending on which Borrelia genospecies infects the patient and may be a consequence of distinct organotropism between species. In the US, B. burgdorferi sensu stricto is the most commonly reported genospecies and infection can manifest as mild to severe symptoms. Different genotypes of B. burgdorferi sensu stricto may be responsible for causing varying degrees of clinical manifestations. While the majority of Lyme borreliae-infected patients fully recover with antibiotic treatment, approximately 15% of infected individuals experience long-term neurological and psychological symptoms that are unresponsive to antibiotics. Currently, long-term antibiotic treatment remains the only FDA-approved option for those suffering from these chronic effects. Here, we discuss the current knowledge pertaining to B. burgdorferi sensu stricto infection in the central nervous system (CNS), termed Lyme neuroborreliosis (LNB), within North America and specifically the United States. We explore the molecular mechanisms of spirochete entry into the brain and the role B. burgdorferi sensu stricto genotypes play in CNS infectivity. Understanding infectivity can provide therapeutic targets for LNB treatment and offer public health understanding of the B. burgdorferi sensu stricto genotypes that cause long-lasting symptoms.

Exploring a possibility of using Raman spectroscopy for detection of Lyme disease

Lyme disease (LD), one of the most prevalent tick-borne diseases in the United States (US), is caused by Borreliella burgdorferi sensu stricto (Bb). To date, in the US, LD diagnostics is primarily based on validated two-tiered serological testing, which overall exhibits low sensitivity among other drawbacks. In the present study, a potential of Raman spectroscopy (RS) to detect Bb infection in mice has been explored. For that, C3H mice were infected with wild-type Bb strains, 297, B31, or B31-derived mutant, ∆vlsE. Blood samples taken prior to and post Bb infection were subjected to RS. The data demonstrated that RS did not directly detect Bb spirochetes in blood, but rather sensed biochemical changes associated with Bb infection. Despite Bb infection-associated blood changes detectable by RS were very limited, the partial least square discriminant analysis showed that the average true positive rates were 86% for 297 and 89% for B31 and ∆vlsE.

New Zealand White Rabbits Effectively Clear Borrelia burgdorferi B31 despite the Bacterium's Functional vlsE Antigenic Variation System

Borrelia burgdorferi is a tick-borne bacterium responsible for approximately 300,000 annual cases of Lyme disease (LD) in the United States, with increasing incidences in other parts of the world. The debilitating nature of LD is mainly attributed to the ability of B. burgdorferi to persist in patients for many years despite strong anti-Borrelia antibody responses. Antimicrobial treatment of persistent infection is challenging. Similar to infection of humans, B. burgdorferi establishes long-term infection in various experimental animal models except for New Zealand White (NZW) rabbits, which clear the spirochete within 4 to 12 weeks. LD spirochetes have a highly evolved antigenic variation vls system, on the lp28-1 plasmid, where gene conversion results in surface expression of the antigenically variable VlsE protein. VlsE is required for B. burgdorferi to establish persistent infection by continually evading otherwise potent antibodies. Since the clearance of B. burgdorferi is mediated by humoral immunity in NZW rabbits, the previously reported results that LD spirochetes lose lp28-1 during rabbit infection could potentially explain the failure of B. burgdorferi to persist. However, the present study unequivocally disproves that previous finding by demonstrating that LD spirochetes retain the vls system. However, despite the vls system being fully functional, the spirochete fails to evade anti-Borrelia antibodies of NZW rabbits. In addition to being protective against homologous and heterologous challenges, the rabbit antibodies significantly ameliorate LD-induced arthritis in persistently infected mice. Overall, the current data indicate that NZW rabbits develop a protective antibody repertoire, whose specificities, once defined, will identify potential candidates for a much-anticipated LD vaccine.

Heterogeneity of Borrelia burgdorferi Sensu Stricto Population and Its Involvement in Borrelia Pathogenicity: Study on Murine Model with Specific Emphasis on the Skin Interface

Lyme disease is a multisystemic disorder caused by B. burgdorferi sl. The molecular basis for specific organ involvement is poorly understood. The skin plays a central role in the development of Lyme disease as the entry site of B. burgdorferi in which specific clones are selected before dissemination. We compared the skin inflammatory response (antimicrobial peptides, cytokines and chemokines) elicited by spirochete populations recovered from patients presenting different clinical manifestations. Remarkably, these spirochete populations induced different inflammatory profiles in the skin of C3H/HeN mice. As spirochete population transmitted into the host skin is heterogeneous, we isolated one bacterial clone from a population recovered from a patient with neuroborreliosis and compared its virulence to the parental population. This clone elicited a strong cutaneous inflammatory response characterized by MCP-1, IL-6 and antimicrobial peptides induction. Mass spectrometry of this clone revealed 110 overexpressed proteins when compared with the parental population. We further focused on the expression of nine bacterial surface proteins. bb0347 coding for a protein that interacts with host fibronectin, allowing bacterial adhesion to vascular endothelium and extracellular matrix, was found to be induced in host skin with another gene bb0213 coding for a hypothetical protein. These findings demonstrate the heterogeneity of the B. burgdorferi ss population and the complexity of the interaction involved early in the skin.

Borrelia burgdorferi promotes the establishment of Babesia microti in the northeastern United States

Babesia microti and Borrelia burgdorferi, the respective causative agents of human babesiosis and Lyme disease, are maintained in their enzootic cycles by the blacklegged tick (Ixodes scapularis) and use the white-footed mouse (Peromyscus leucopus) as primary reservoir host. The geographic range of both pathogens has expanded in the United States, but the spread of babesiosis has lagged behind that of Lyme disease. Several studies have estimated the basic reproduction number (R₀) for B. microti to be below the threshold for persistence (<1), a finding that is inconsistent with the persistence and geographic expansion of this pathogen. We tested the hypothesis that host coinfection with B. burgdorferi increases the likelihood of B. microti transmission and establishment in new areas. We fed I. scapularis larva on P. leucopus mice that had been infected in the laboratory with B. microti and/or B. burgdorferi. We observed that coinfection in mice increases the frequency of B. microti infected ticks. To identify the ecological variables that would increase the probability of B. microti establishment in the field, we integrated our laboratory data with field data on tick burden and feeding activity in an R₀ model. Our model predicts that high prevalence of B. burgdorferi infected mice lowers the ecological threshold for B. microti establishment, especially at sites where larval burden on P. leucopus is lower and where larvae feed simultaneously or soon after nymphs infect mice, when most of the transmission enhancement due to coinfection occurs. Our studies suggest that B. burgdorferi contributes to the emergence and expansion of B. microti and provides a model to predict the ecological factors that are sufficient for emergence of B. microti in the wild.

Molecular Typing of Borrelia burgdorferi

Borrelia burgdorferi sensu lato is a group of spirochetes belonging to the genus Borrelia in the family of Spirochaetaceae. The spirochete is transmitted between reservoirs and hosts by ticks of the family Ixodidae. Infection with B. burgdorferi in humans causes Lyme disease or Lyme borreliosis. Currently, 20 Lyme disease-associated Borrelia species and more than 20 relapsing fever-associated Borrelia species have been described. Identification and differentiation of different Borrelia species and strains is largely dependent on analyses of their genetic characteristics. A variety of molecular techniques have been described for Borrelia isolate speciation, molecular epidemiology, and pathogenicity studies. In this unit, we focus on three basic protocols, PCR-RFLP-based typing of the rrs-rrlA and rrfA-rrlB ribosomal spacer, ospC typing, and MLST. These protocols can be employed alone or in combination for characterization of B. burgdorferi isolates or directly on uncultivated organisms in ticks, mammalian host reservoirs, and human clinical specimens.

Induction of type I and type III interferons by Borrelia burgdorferi correlates with pathogenesis and requires linear plasmid 36

The capacity for Borrelia burgdorferi to cause disseminated infection in humans or mice is associated with the genotype of the infecting strain. The cytokine profiles elicited by B. burgdorferi clinical isolates of different genotype (ribosomal spacer type) groups were assessed in a human PBMC co-incubation model. RST1 isolates, which are more frequently associated with disseminated Lyme disease in humans and mice, induced significantly higher levels of IFN-α and IFN-λ1/IL29 relative to RST3 isolates, which are less frequently associated with disseminated infection. No differences in the protein concentrations of IFN-γ, IL-1β, IL-6, IL-8, IL-10 or TNF-α were observed between isolates of differing genotype. The ability of B. burgdorferi to induce type I and type III IFNs was completely dependent on the presence of linear plasmid (lp) 36. An lp36-deficient B. burgdorferi mutant adhered to, and was internalized by, PBMCs and specific dendritic cell (DC) subsets less efficiently than its isogenic B31 parent strain. The association defect with mDC1s and pDCs could be restored by complementation of the mutant with the complete lp36. The RST1 clinical isolates studied were found to contain a 2.5-kB region, located in the distal one-third of lp36, which was not present in any of the RST3 isolates tested. This divergent region of lp36 may encode one or more factors required for optimal spirochetal recognition and the production of type I and type III IFNs by human DCs, thus suggesting a potential role for DCs in the pathogenesis of B. burgdorferi infection.

Inter- and intra-specific pan-genomes of Borrelia burgdorferi sensu lato: genome stability and adaptive radiation

BACKGROUND

Lyme disease is caused by spirochete bacteria from the Borrelia burgdorferi sensu lato (B. burgdorferi s.l.) species complex. To reconstruct the evolution of B. burgdorferi s.l. and identify the genomic basis of its human virulence, we compared the genomes of 23 B. burgdorferi s.l. isolates from Europe and the United States, including B. burgdorferi sensu stricto (B. burgdorferi s.s., 14 isolates), B. afzelii (2), B. garinii (2), B. "bavariensis" (1), B. spielmanii (1), B. valaisiana (1), B. bissettii (1), and B. "finlandensis" (1).

RESULTS

Robust B. burgdorferi s.s. and B. burgdorferi s.l. phylogenies were obtained using genome-wide single-nucleotide polymorphisms, despite recombination. Phylogeny-based pan-genome analysis showed that the rate of gene acquisition was higher between species than within species, suggesting adaptive speciation. Strong positive natural selection drives the sequence evolution of lipoproteins, including chromosomally-encoded genes 0102 and 0404, cp26-encoded ospC and b08, and lp54-encoded dbpA, a07, a22, a33, a53, a65. Computer simulations predicted rapid adaptive radiation of genomic groups as population size increases.

CONCLUSIONS

Intra- and inter-specific pan-genome sizes of B. burgdorferi s.l. expand linearly with phylogenetic diversity. Yet gene-acquisition rates in B. burgdorferi s.l. are among the lowest in bacterial pathogens, resulting in high genome stability and few lineage-specific genes. Genome adaptation of B. burgdorferi s.l. is driven predominantly by copy-number and sequence variations of lipoprotein genes. New genomic groups are likely to emerge if the current trend of B. burgdorferi s.l. population expansion continues.

Multilocus sequence typing of Borrelia burgdorferi suggests existence of lineages with differential pathogenic properties in humans

The clinical manifestations of Lyme disease, caused by Borrelia burgdorferi, vary considerably in different patients, possibly due to infection by strains with varying pathogenicity. Both rRNA intergenic spacer and ospC typing methods have proven to be useful tools for categorizing B. burgdorferi strains that vary in their tendency to disseminate in humans. Neither method, however, is suitable for inferring intraspecific relationships among strains that are important for understanding the evolution of pathogenicity and the geographic spread of disease. In this study, multilocus sequence typing (MLST) was employed to investigate the population structure of B. burgdorferi recovered from human Lyme disease patients. A total of 146 clinical isolates from patients in New York and Wisconsin were divided into 53 sequence types (STs). A goeBURST analysis, that also included previously published STs from the northeastern and upper Midwestern US and adjoining areas of Canada, identified 11 major and 3 minor clonal complexes, as well as 14 singletons. The data revealed that patients from New York and Wisconsin were infected with two distinct, but genetically and phylogenetically closely related, populations of B. burgdorferi. Importantly, the data suggest the existence of B. burgdorferi lineages with differential capabilities for dissemination in humans. Interestingly, the data also indicate that MLST is better able to predict the outcome of localized or disseminated infection than is ospC typing.

Structure of rrn operons in pathogenic non-cultivable treponemes: sequence but not genomic position of intergenic spacers correlates with classification of Treponema pallidum and Treponema paraluiscuniculi strains

This study examined the sequences of the two rRNA (rrn) operons of pathogenic non-cultivable treponemes, comprising 11 strains of T. pallidum ssp. pallidum (TPA), five strains of T. pallidum ssp. pertenue (TPE), two strains of T. pallidum ssp. endemicum (TEN), a simian Fribourg-Blanc strain and a rabbit T. paraluiscuniculi (TPc) strain. PCR was used to determine the type of 16S–23S ribosomal intergenic spacers in the rrn operons from 30 clinical samples belonging to five different genotypes. When compared with the TPA strains, TPc Cuniculi A strain had a 17 bp deletion, and the TPE, TEN and Fribourg-Blanc isolates had a deletion of 33 bp. Other than these deletions, only 17 heterogeneous sites were found within the entire region (excluding the 16S–23S intergenic spacer region encoding tRNA-Ile or tRNA-Ala). The pattern of nucleotide changes in the rrn operons corresponded to the classification of treponemal strains, whilst two different rrn spacer patterns (Ile/Ala and Ala/Ile) appeared to be distributed randomly across species/subspecies classification, time and geographical source of the treponemal strains. It is suggested that the random distribution of tRNA genes is caused by reciprocal translocation between repetitive sequences mediated by a recBCD-like system.

Comparative molecular analyses of Borrelia burgdorferi sensu stricto strains B31 and N40D10/E9 and determination of their pathogenicity

Background

Lyme disease in the United States is caused primarily by B. burgdorferi sensu stricto while other species are also prevalent in Europe. Genetic techniques have identified several chromosomal and plasmid-borne regulatory and virulence factors involved in Lyme pathogenesis. B31 and N40 are two widely studied strains of B. burgdorferi, which belong to two different 16 S-23 S rRNA spacer types (RST) and outer surface protein C (OspC) allelic groups. However, the presence of several known virulence factors in N40 has not been investigated. This is the first comprehensive study that compared these two strains both in vitro and using the mouse model of infection.

Results

Phylogenetic analyses predict B31 to be more infectious. However, our studies here indicate that N40D10/E9 is more infectious than the B31 strain at lower doses of inoculation in the susceptible C3H mice. Based-upon a careful analyses of known adhesins of these strains, it is predicted that the absence of a known fibronectin-glycosaminoglycan binding adhesin, bbk32, in the N40 strain could at least partially be responsible for reduction in its binding to Vero cells in vitro. Nevertheless, this difference does not affect the infectivity of N40D10/E9 strain. The genes encoding known regulatory and virulence factors critical for pathogenesis were detected in both strains. Differences in the protein profiles of these B. burgdorferi strains in vitro suggest that the novel, differentially expressed molecules may affect infectivity of B. burgdorferi. Further exacerbation of these molecular differences in vivo could affect the pathogenesis of spirochete strains.

Conclusion

Based upon the studies here, it can be predicted that N40D10/E9 disseminated infection at lower doses may be enhanced by its lower binding to epithelial cells at the site of inoculation due to the absence of BBK32. We suggest that complete molecular analyses of virulence factors followed by their evaluation using the mouse infection model should form the basis of determining infectivity and pathogenicity of different strains rather than simple phylogenetic group analyses. This study further emphasizes a need to investigate multiple invasive strains of B. burgdorferi to fully appreciate the pathogenic mechanisms that contribute to Lyme disease manifestations.

Detection of established virulence genes and plasmids to differentiate Borrelia burgdorferi strains

Borrelia burgdorferi sensu stricto is the major causative agent of Lyme disease in the United States, while B. garinii and B. afzelii are more prevalent in Europe. The highly complex genome of B. burgdorferi is comprised of a linear chromosome and a large number of variably sized linear and circular plasmids. Many plasmids of this spirochete are unstable during its culture in vitro. Given that many of the B. burgdorferi virulence factors identified to date are plasmid encoded, spirochetal plasmid content determination is essential for genetic analysis of Lyme pathogenesis. Although PCR-based assays facilitate plasmid profiling of sequenced B. burgdorferi strains, a rapid genetic content determination strategy for nonsequenced strains has not yet been described. In this study, we combined pulsed-field gel electrophoresis (PFGE) and Southern hybridization for detection of genes encoding known virulence factors, ribosomal RNA gene spacer restriction fragment length polymorphism types (RSTs), ospC group determination, and sequencing of the variable dbpA and ospC genes. We show that two strains isolated from the same tick and both originally named N40 are in fact very distinct. Furthermore, we failed to detect bbk32, which encodes a fibronectin-binding adhesin, in one "N40" strain. Thus, two distinct strains that show different plasmid profiles, as determined by PFGE and PCR, were isolated from the same tick and vary in their ospC and dbpA sequences. However, both belong to group RST3B.

The expanding Lyme Borrelia complex--clinical significance of genomic species?

Ten years after the discovery of spirochaetes as agents of Lyme disease in 1982 in the USA, three genomic species had diverged from the phenotypically heterogeneous strains of Borrelia burgdorferi isolated in North America and Europe: Borrelia afzelii, B. burgdorferi sensu stricto (further B. burgdorferi), and Borrelia garinii. Whereas B. burgdorferi remained the only human pathogen in North America, all three species are aetiological agents of Lyme borreliosis in Europe. Another seven genospecies were described in the 1990s, including species from Asia (Borrelia japonica, Borrelia turdi, and B. tanukii), North America (Borrelia andersonii), Europe (Borrelia lusitaniae and Borrelia valaisiana), and from Europe and Asia (Borrelia bissettii). Another eight species were delineated in the years up to 2010: Borrelia sinica (Asia), Borrelia spielmanii (Europe), Borrelia yangtze (Asia), Borrelia californiensis, Borrelia americana, Borrelia carolinensis (North America), Borrelia bavariensis (Europe), and Borrelia kurtenbachii (North America). Of these 18 genomic species B. afzelii, B. burgdorferi and B. garinii are the confirmed agents of localized, disseminated and chronic manifestations of Lyme borreliosis, whereas B. spielmanii has been detected in early skin disease, and B. bissettii and B. valaisiana have been detected in specimens from single cases of Lyme borreliosis. The clinical role of B. lusitaniae remains to be substantiated.

Uncoordinated phylogeography of Borrelia burgdorferi and its tick vector, Ixodes scapularis

Vector-borne microbes necessarily co-occur with their hosts and vectors, but the degree to which they share common evolutionary or biogeographic histories remains unexplored. We examine the congruity of the evolutionary and biogeographic histories of the bacterium and vector of the Lyme disease system, the most prevalent vector-borne disease in North America. In the eastern and midwestern US, Ixodes scapularis ticks are the primary vectors of Borrelia burgdorferi, the bacterium that causes Lyme disease. Our phylogeographic and demographic analyses of the 16S mitochondrial rDNA suggest that northern I. scapularis populations originated from very few migrants from the southeastern US that expanded rapidly in the Northeast and subsequently in the Midwest after the recession of the Pleistocene ice sheets. Despite this historical gene flow, current tick migration is restricted even between proximal sites within regions. In contrast, B. burgdorferi suffers no barriers to gene flow within the northeastern and midwestern regions but shows clear interregional migration barriers. Despite the intimate association of B. burgdorferi and I. scapularis, the population structure, evolutionary history, and historical biogeography of the pathogen are all contrary to its arthropod vector. In the case of Lyme disease, movements of infected vertebrate hosts may play a larger role in the contemporary expansion and homogenization of the pathogen than the movement of tick vectors whose populations continue to bear the historical signature of climate-induced range shifts.

Evolution of northeastern and midwestern Borrelia burgdorferi, United States

Differences in animal ecology or human behavior may account for differences in human incidence in the 2 regions.

The per capita incidence of human Lyme disease in the northeastern United States is more than twice that in the Midwest. However, the prevalence of Borrelia burgdorferi, the bacterium that causes Lyme disease, in the tick vector is nearly identical in the 2 regions. The disparity in human Lyme disease incidence may result from a disparity in the human invasiveness of the bacteria in the Northeast and Midwest caused by fundamentally different evolutionary histories. B. burgdorferi populations in the Northeast and Midwest are geographically isolated, enabling evolutionary divergence in human invasiveness. However, we found that B. burgdorferi populations in the Northeast and Midwest shared a recent common ancestor, which suggests that substantial evolutionary divergence in human invasiveness has not occurred. We propose that differences in either animal ecology or human behavior are the root cause of the differences in human incidence between the 2 regions.

Prevalence of Borrelia burgdorferi sensu lato in rodents from Gansu, northwestern China

Background

Lyme disease is a multi-organ infection disease caused by Borrelia burgdorferi sensu lato. Lyme disease was first documented in north-east China in 1986. Since then more than 20 provinces in China were confirmed the existence of nature foci of Lyme disease. In the present study, a molecular epidemiological survey was conducted to investigate the presence of Borrelia burgdorferi sensu lato in rodents from Gansu Province for the first time.

Result

A total of 140 rodents of 7 species were examined for Borrelia burgdorferi sensu lato. by nested-PCR and culture isolation. The overall infection rate was 22.86%. Two rodent species most frequently trapped were responsible for all positive. 3 strains were isolated from Apodemus agrarius, which belonged to B. garinii, 1 strain isolated from Rattus losea was identified as B. afzelii.

Conclusion

The study firstly showed the role of rodents in maintaining the pathogen of Lyme disease in the environment from Gansu Province and there existed at least two genotypes of Lyme disease spirochaetes in rodents.

Effects of tick control by acaricide self-treatment of white-tailed deer on host-seeking tick infection prevalence and entomologic risk for Ixodes scapularis-borne pathogens

We evaluated the effects of tick control by acaricide self-treatment of white-tailed deer on the infection prevalence and entomologic risk for three Ixodes scapularis-borne bacteria in host-seeking ticks. Ticks were collected from vegetation in areas treated with the "4-Poster" device and from control areas over a 6-year period in five geographically diverse study locations in the Northeastern United States and tested for infection with two known agents of human disease, Borrelia burgdorferi and Anaplasma phagocytophilum, and for a novel relapsing fever-group spirochete related to Borrelia miyamotoi. Overall, 38.2% of adults and 12.5% of nymphs were infected with B. burgdorferi; 8.5% of adults and 4.2% of nymphs were infected with A. phagocytophilum; and 1.9% of adults and 0.8% of nymphs were infected with B. miyamotoi. In most cases, treatment with the 4-Poster device was not associated with changes in the prevalence of infection with any of these three microorganisms among nymphal or adult ticks. However, the density of nymphs infected with B. burgdorferi, and consequently the entomologic risk for Lyme disease, was reduced overall by 68% in treated areas compared to control areas among the five study sites at the end of the study. The frequency of bacterial coinfections in ticks was generally equal to the product of the proportion of ticks infected with a single bacterium, indicating that enzootic maintenance of these pathogens is independent. We conclude that controlling ticks on deer by self-application of acaricide results in an overall decrease in the human risk for exposure to these three bacterial agents, which is due solely to a reduction in tick density.

Population structure of the lyme borreliosis spirochete Borrelia burgdorferi in the western black-legged tick (Ixodes pacificus) in Northern California

Factors potentially contributing to the lower incidence of Lyme borreliosis (LB) in the far-western than in the northeastern United States include tick host-seeking behavior resulting in fewer human tick encounters, lower densities of Borrelia burgdorferi-infected vector ticks in peridomestic environments, and genetic variation among B. burgdorferi spirochetes to which humans are exposed. We determined the population structure of B. burgdorferi in over 200 infected nymphs of the primary bridging vector to humans, Ixodes pacificus, collected in Mendocino County, CA. This was accomplished by sequence typing the spirochete lipoprotein ospC and the 16S-23S rRNA intergenic spacer (IGS). Thirteen ospC alleles belonging to 12 genotypes were found in California, and the two most abundant, ospC genotypes H3 and E3, have not been detected in ticks in the Northeast. The most prevalent ospC and IGS biallelic profile in the population, found in about 22% of ticks, was a new B. burgdorferi strain defined by ospC genotype H3. Eight of the most common ospC genotypes in the northeastern United States, including genotypes I and K that are associated with disseminated human infections, were absent in Mendocino County nymphs. ospC H3 was associated with hardwood-dominated habitats where western gray squirrels, the reservoir host, are commonly infected with LB spirochetes. The differences in B. burgdorferi population structure in California ticks compared to the Northeast emphasize the need for a greater understanding of the genetic diversity of spirochetes infecting California LB patients.

Pattern of proinflammatory cytokine induction in RAW264.7 mouse macrophages is identical for virulent and attenuated Borrelia burgdorferi

Lyme disease pathogenesis results from a complex interaction between Borrelia burgdorferi and the host immune system. The intensity and nature of the inflammatory response of host immune cells to B. burgdorferi may be a determining factor in disease progression. Gene array analysis was used to examine the expression of genes encoding cytokines, chemokines, and related factors in the joint tissue of infected C3H/HeJ mice and in a murine macrophage-like cell line in response to a disseminating or attenuated clinical isolate of B. burgdorferi. Both isolates elicited a robust proinflammatory response in RAW264.7 cells characterized by an increase in transcript levels of genes encoding CC and CXC chemokines, proinflammatory cytokines, and TNF superfamily members. Transcription of genes encoding IL-1beta, IL-6, MCP-1, MIP-1alpha, CXCR4, and TLR2 induced in RAW264.7 cells by either live or heat-killed spirochetes did not differ significantly at any time point over a 24-h period, nor was there a difference in the protein levels of IL-10, TNF-alpha, IL-6, and IL-12p70 in culture supernatants. Thus, induction of host macrophage expression of proinflammatory mediators by host macrophages does not contribute to the differential pathogenicity of different B. burgdorferi strains.

The propensity of different Borrelia burgdorferi sensu stricto genotypes to cause disseminated infections in humans

Lineages of Borrelia burgdorferi, the bacterium that causes Lyme disease, can be characterized by distinct alleles at the outer surface protein C (ospC) locus. The lineages marked by ospC genotypes have been shown to be differentially invasive in different species of mammals, including humans; genotypes A, B, I, and K effectively disseminate to human blood and cerebrospinal fluid. In this report, we extend the sample of genotypes isolated from human blood to include genotypes N, H, C, M, and D, and rank each by their probability of disseminating from ticks to the blood of humans. Our results demonstrate that only some genotypes of B. burgdorferi present in ticks have a high propensity to disseminate in humans.

Hematogenous dissemination in early Lyme disease

Hematogenous dissemination has long been considered an important pathogenetic event in Lyme borreliosis but has been hard to document and characterize due to insensitive blood culture methods. In a series of recent investigations involving adult patients from the United States with erythema migrans, it was concluded that plasma was a better source of culture material than serum or whole blood, and yield correlated directly with the volume of material cultured. The rate of recovery of Borrelia burgdorferi from 9 mL of plasma exceeded 40%. Both the genotype of the strain of B. burgdorferi introduced by the tick and host factors, such as having a first episode of Lyme borreliosis and being more than 55 years of age, appear to affect the risk of hematogenous dissemination. Although the majority of spirochetemic patients are symptomatic, spirochetemia can be a subclinical event. In summary, hematogenous dissemination is a common and important feature of early Lyme borreliosis in the United States. The high rate, early onset and prolonged duration of risk of spirochetemia probably explain why untreated patients with erythema migrans may develop objective clinical manifestations at a distant anatomic site.

Borrelia burgdorferi spirochetes that harbor only a portion of the lp28-1 plasmid elicit antibody responses detectable with the C6 test for Lyme disease

Detection of antibody to C6, a peptide that reproduces the sequence of the sixth invariable region within the central domain of the VlsE protein of Borrelia burgdorferi, is used currently for the serologic diagnosis of Lyme disease in humans. B. burgdorferi isolates taken from infected humans can be categorized into specific genetic subtypes (designated RST1, -2, and -3) by restriction fragment length polymorphisms in the 16S to 23S rRNA spacer sequence. Many of these, usually categorized as RST2, retain only segments of the linear plasmid lp28-1, which encodes VlsE. The VlsE genetic region is retained, but altered expression of this molecule could affect diagnosis by the C6 enzyme-linked immunosorbent assay (ELISA). Serum samples from patients infected with each of the three genotypes and from mice infected with three RST2 isolates were tested with the C6 ELISA. Such isolates elicited marked C6 responses in infected mice. The sensitivity of C6 antibody detection in patients infected with RST2 spirochetes was statistically indistinguishable from detection of RST1 and RST3 infections. These findings demonstrate that diagnosis by C6 ELISA remains effective for infection with all B. burgdorferi genotypes, including those with incomplete lp28-1 plasmids.

Borrelia burgdorferi genetic markers and disseminated disease in patients with early Lyme disease

Three genetic markers of Borrelia burgdorferi have been associated with disseminated disease: the OspC type, the 16S-23S rRNA intergenic spacer type (RST), and vlsE. Here, we modified previous methods so as to identify the three markers by PCR and restriction fragment length polymorphism in parallel, analyzed B. burgdorferi isolates from erythema migrans (EM) skin lesions in 91 patients, and correlated the results with evidence of dissemination. OspC type A was found approximately twice as frequently in patients with disseminated disease, whereas type K was identified approximately twice as often in those without evidence of dissemination, but these trends were not statistically significant. The remaining seven types identified were found nearly equally in patients with or without evidence of dissemination. RST 1 strains were significantly associated with dissemination (P=0.03), whereas RST 2 and RST 3 strains tended to have an inverse association with this outcome. The vlsE gene was identified in all 91 cases, using primer sets specific for an N-terminal sequence of B. burgdorferi strain B31 (vlsEB31) or strain 297 (vlsE297), but neither marker was associated with dissemination. Specific combinations of the three genetic markers usually occurred together. OspC type A was always found with RST 1 and vlsEB31, type K was always identified with RST 2 and more often with vlsE297, and types E and I were almost always found with RST 3 and equally often with vlsEB31 and vlsE297. We conclude that B. burgdorferi strains vary in their capacity to disseminate, but almost all strains isolated from EM lesions sometimes caused disseminated disease.

Comparative genome hybridization reveals substantial variation among clinical isolates of Borrelia burgdorferi sensu stricto with different pathogenic properties

Clinical and murine studies suggest that there is a differential pathogenicity of different genotypes of Borrelia burgdorferi, the spirochetal agent of Lyme disease. Comparative genome hybridization was used to explore the relationship between different genotypes. The chromosomes of all studied isolates were highly conserved (>93%) with respect to both sequence and gene order. Plasmid sequences were substantially more diverse. Plasmids lp54, cp26, and cp32 were present in all tested isolates, and their sequences and gene order were conserved. The majority of linear plasmids showed variation both in terms of presence among different isolates and in terms of sequence and gene order. The data strongly imply that all B. burgdorferi clinical isolates contain linear plasmids related to each other, but the structure of these replicons may vary substantially from isolate to isolate. These alterations include deletions and presumed rearrangements that are likely to result in unique plasmid elements in many isolates. There is a strong correlation between complete genome hybridization profiles and other typing methods, which, in turn, also correlate to differences in pathogenicity. Because there is substantially less variation in the chromosomal and circular plasmid portions of the genome, the major differences in open reading frame content and genomic diversity among isolates are linear plasmid driven.

MyD88 deficiency enhances acquisition and transmission of Borrelia burgdorferi by Ixodes scapularis ticks

Borrelia burgdorferi strains exhibit various degrees of infectivity and pathogenicity in mammals, which may be due to their relative ability to evade initial host immunity. Innate immune cells recognize B. burgdorferi by Toll-like receptors (TLRs) that use the intracellular molecule MyD88 to mediate effector functions. To determine whether impaired TLR signaling enhances Ixodes scapularis acquisition of B. burgdorferi, we fed nymphs on wild-type (WT) and MyD88-/- mice previously infected with two clinical isolates of B. burgdorferi, BL206, a high-virulence strain, and B348, an attenuated strain. Seventy-three percent of the nymphs that fed on BL206-infected WT mice and 40% of the nymphs that fed on B348-infected WT mice acquired B. burgdorferi, whereas 100% of the nymphs that fed on MyD88-/- mice became infected, irrespective of B. burgdorferi strain. Ticks that acquired infection after feeding on MyD88-/- mice harbored more spirochetes than those that fed on WT mice, as assessed by quantitative PCR for B. burgdorferi DNA. Vector transmission of BL206 and B348 was also enhanced when MyD88-/- mice were the blood meal hosts, with the mean pathogen burden at the skin inoculation site significantly higher than levels in WT mice. These results show that the absence of MyD88 facilitates passage of both low- and high-infectivity B. burgdorferi strains between the tick vector and the mammal and enhances the infectivity of a low-infectivity B. burgdorferi strain.

Co-evolution of the outer surface protein C gene (ospC) and intraspecific lineages of Borrelia burgdorferi sensu stricto in the northeastern United States

Clinical and tick isolates of Borrelia burgdorferi sensu stricto, the bacterial agent of Lyme disease, from the northeastern United States were sequenced at 12 loci located on the main chromosome and 7 plasmids (lp54, cp26, cp9, lp17, lp25, lp28-2, and lp38). The outer surface protein C gene (ospC) showed the highest number (12) of major alleles (defined as alleles differing by 5% or more in nucleotide sequence) while other ORFs had only two to four major alleles. A non-recombining chromosomal marker, the rrs-rrlA ribosomal RNA spacer, was used to infer the intraspecific phylogeny among these B. burgdorferi isolates. We were thus able to analyze the multilocus genotypes in the context of a B. burgdorferi intraspecific phylogeny. Except for ospC, sequence variations at plasmid-borne loci showed broad inconsistency with the intraspecific phylogeny, supporting DNA exchanges mediated by plasmid transfers. The multilocus linkage frequently observed in B. burgdorferi populations is due more likely to a "founder effect" than to a lack of recombination. The exceptional phylogenetic consistency of ospC, in conjunction with its selectively maintained high intraspecific diversity, suggested a dominant role ospC plays in the initiation and maintenance of adaptive differentiation in B. burgdorferi.

Comparison of isolation rate of Borrelia burgdorferi sensu lato in MKP and BSK-II medium

Different media have been utilized for borrelial cultivation. The aim of the present study was to evaluate the isolation rate of Borrelia burgdorferi sensu lato from two commonly used media, i.e. modified Kelly-Pettenkofer (MKP) and Barbour-Stoenner-Kelly II (BSK-II) medium, and to compare the isolated strains with regard to their phenotypic and genotypic characteristics. Skin biopsy specimens of 2 x 2 x 4 mm were taken from the peripheral site of human solitary erythema lesions and were divided in two pieces, one of which was inoculated into MKP and the other one into BSK-II medium. Species analysis of the obtained strains was performed and their plasmid and protein profiles were determined. Borrelia strains were isolated from 48/96 patients (50%) with erythema migrans. We obtained in 26/48 patients (54%) from MKP as well as from BSK-II, in 11 patients (23%) only from MKP, and in another 11 (23%) only from BSK-II medium a positive result. B. afzelii was isolated from 43 patients (23 were positive in both media, nine in MKP only and 11 in BSK-II medium only), while B. garinii was isolated from five patients (in three from both media, in two from MKP only). All strains of the obtained strain pairs were identical according to species and the type within the species. Plasmid profiles were identical in 17/21 B. afzelii strain pairs (81%) and in 1/3 B. garinii strain pairs; in 6/24 strain pairs, distinctions in the number of plasmids or in their molecular mass were present. Differences in the protein profile were found in 7/24 strain pairs (29%). The distinctions were uniform and were limited to the expression of OspC. In conclusion, our study showed comparable Borrelia isolation rates from MKP and BSK-II medium. The results of the present study indicate that human patients with Lyme borreliosis may simultaneously harbor heterogeneous B. burgdorferi s.l. strains.

Comparative transcriptional profiling of Borrelia burgdorferi clinical isolates differing in capacities for hematogenous dissemination

Borrelia burgdorferi, the etiologic agent of Lyme disease, is genetically heterogeneous. Previous studies have shown a significant association between the frequency of hematogenous dissemination in Lyme disease patients and the genotype of the infecting B. burgdorferi strain. Comparative transcriptional profiling of two representative clinical isolates with distinct genotypes (BL206 and B356) was undertaken. A total of 78 open reading frames (ORFs) had expression levels that differed significantly between the two isolates. A number of genes with potential involvement in nutrient uptake (BB0603, BBA74, BB0329, BB0330, and BBB29) have significantly higher expression levels in isolate B356. Moreover, nearly 25% of the differentially expressed genes are predicted to be localized on the cell surface, implying that these two isolates have cell surface properties that differ considerably. One of these genes, BBA74, encodes a protein of 257 amino acid residues that has been shown to possess porin activity. BBA74 transcript level was >20-fold higher in B356 than in BL206, and strain B356 contained three- to fivefold more BBA74 protein. BBA74 was disrupted by the insertion of a kanamycin resistance cassette into the coding region. The growth rates of both wild-type and mutant strains were essentially identical, and cultures reached the same final cell densities. However, the mutant strains consistently showed prolonged lags of 2 to 5 days prior to the induction of log-phase growth compared to wild-type strains. It is tempting to speculate that the absence of BBA74 interferes with the enhanced nutrient uptake that may be required for the entry of cells into log-phase growth. These studies demonstrate the value of comparative transcriptional profiling for identifying differences in the transcriptomes of B. burgdorferi clinical isolates that may provide clues to pathogenesis. The 78 ORFs identified here are a good starting point for the investigation of factors involved in the hematogenous dissemination of B. burgdorferi.

Three multiplex assays for detection of Borrelia burgdorferi sensu lato and Borrelia miyamotoi sensu lato in field-collected Ixodes nymphs in North America

Two hundred fifty New Jersey field-collected Ixodes scapularis Say ticks and 17 Colorado Ixodes spinipalpis Hadwen & Nuttall ticks were tested using three separate multiplex real-time polymerase chain reaction (PCR) assays. One assay targets the rrs-rrlA IGS region of Borrelia spp. to detect Borrelia burgdorferi sensu lato (s.l.) and Borrelia miyamotoi s.l. The second assay targets the ospA region of B. burgdorferi s.l. to detect B. burgdorferi sensu stricto (s.s.), Borrelia bissettii, and Borrelia andersonii. The final assay targets the glpQ region of B. miyamotoi s.l. to differentiate B. miyamotoi LB-2001 and Borrelia lonestari. A testing scheme combining these tests yielded 18% of tested I. scapularis ticks surveyed from New Jersey positive for B. burgdorferi s.s., 3.2% I. scapularis ticks positive for B. miyamotoi LB-2001, and 41.2% I. spinipalpis ticks positive for B. bissettii surveyed from Colorado.

Association between human leukocyte antigen class II alleles and genotype of Borrelia burgdorferi in patients with early lyme disease

BACKGROUND

On the basis of a polymerase chain reaction-restriction fragment-length polymorphism analysis of the 16S-23S ribosomal DNA intergenic spacer, clinical isolates of Borrelia burgdorferi can be classified into 3 genotypes designated as RST1, RST2, and RST3. RST1 strains are the most pathogenic, and RST3 strains are the least pathogenic.

METHODS

Human leukocyte antigen (HLA) class II alleles were determined for a group of culture-positive patients with Lyme disease-associated erythema migrans and were evaluated for an association with the genotype of the infecting B. burgdorferi strain.

RESULTS

The DRB1*0101 allele carriage rate was higher in patients infected with RST3 strains (9/25 [36.0%]) than in patients infected with RST1 strains (2/28 [7.1%]) or RST2 strains (7/36 [19.4%]) (P=.010). The same relationship was found for carriage of the DRB1*0101-DQB1*0501 haplotype (P=.018), because of tight linkage disequilibrium. Similar associations could not be demonstrated for any of the other DRB1 and DQB1 alleles or haplotypes that were assessed.

CONCLUSION

The DRB1*0101 allele and the DRB1*0101-DQB1*0501 haplotype may be relevant to the development of infection with strains from the least invasive genotypes of B. burgdorferi.

Comparison of Borrelia burgdorferi sensu lato strains isolated from specimens obtained simultaneously from two different sites of infection in individual patients

The aim of the present study was to analyze and compare Borrelia strains isolated from two different specimens obtained simultaneously from individual patients with Lyme borreliosis. Fifty such patients and 50 corresponding pairs of Borrelia isolates (100 low-propagated strains) were subjected to genotypic and phenotypic analysis, including pulsed-field gel electrophoresis for species identification and plasmid profile determination and protein profile electrophoresis for the assessment of the presence and molecular masses of separated proteins. The strains were isolated from two distinct skin lesions (12 patients), skin and blood (28 patients), skin and cerebrospinal fluid (8 patients), and blood and cerebrospinal fluid (2 patients). Out of 100 isolates, 63 were typed as B. afzelii and 37 as B. garinii. From each individual specimen only a single Borrelia species was cultured. Comparison of 50 Borrelia strain pairs isolated from two different specimens of an individual patient revealed that 12/50 (24%) patients were simultaneously infected with two different Borrelia strains; in 3/50 (6%) patients strains differed at the species level, in 4 out of the remaining 47 (9%) patients a strain difference in plasmid profile was established, while 5 out of the remaining 43 (11%) patient strain pairs differed in regard to the protein profiles of the two concurrently isolated strains. The results of the present study indicate that human patients with Lyme borreliosis may simultaneously harbor different B. burgdorferi sensu lato strains.

Differentiation of bacterial strains by thermal gradient gel electrophoresis using non-GC-clamped PCR primers for the 16S-23S rDNA intergenic spacer region

The method for DNA fingerprinting of the 16S-23S rDNA intergenic spacer region was modified to increase resolution of bacterial strains by thermal gradient gel electrophoresis (TGGE) analysis. By utilizing the high melting temperature region of the tRNA gene located in the middle of the 16S-23S rDNA intergenic spacer region as an internal clamp for TGGE, multiple melting domain problems were solved. PCR primers lacking a stretch of GC-rich sequences (GC-clamp) amplified the intergenic spacer region more efficiently than GC-clamped primers. Therefore, PCR artifacts were avoided by using low, 17-cycle, PCR. The method was successfully applied to diverse bacterial species for strain differentiation by TGGE without requiring a special PCR primer set.

Interaction and transmission of two Borrelia burgdorferi sensu stricto strains in a tick-rodent maintenance system

In the northeastern United States, the Lyme disease agent, Borrelia burgdorferi sensu stricto, is maintained by enzoonotic transmission, cycling between white-footed mice (Peromyscus leucopus) and black-legged ticks (Ixodes scapularis). B. burgdorferi sensu stricto is genetically variable and has been divided into three major genotypes based on 16S-23S ribosomal DNA spacer (RST) analysis. To better understand how genetic differences in B. burgdorferi sensu stricto may influence transmission dynamics in nature, we investigated the interaction between an RST1 and an RST3 strain in a laboratory system with P. leucopus mice and I. scapularis ticks. Two groups of mice were infected with either BL206 (RST1) or B348 (RST3). Two weeks later, experimental mice were challenged with the opposite strain, while control mice were challenged with the same strain as that used for the primary infection. The transmission of BL206 and B348 from infected mice was then determined by xenodiagnosis with uninfected larval ticks at weekly intervals for 42 days. Mice in both experimental groups were permissive for infection with the second strain and were able to transmit both strains to the xenodiagnostic ticks. However, the overall transmission efficiencies of BL206 and B348 were significantly different. BL206 was more efficiently transmitted than B348 to xenodiagnostic ticks. Significantly fewer double infections than expected were detected in xenodiagnostic ticks. The results suggest that some B. burgdorferi sensu stricto strains, such as BL206, may be preferentially maintained in transmission cycles between ticks and white-footed mice. Other strains, such as B348, may be more effectively maintained in different tick-vertebrate transmission cycles.

An ecological approach to preventing human infection: vaccinating wild mouse reservoirs intervenes in the Lyme disease cycle

Many pathogens, such as the agents of West Nile encephalitis and plague, are maintained in nature by animal reservoirs and transmitted to humans by arthropod vectors. Efforts to reduce disease incidence usually rely on vector control or immunization of humans. Lyme disease, for which no human vaccine is currently available, is a commonly reported vector-borne disease in North America and Europe. In a recently developed, ecological approach to disease prevention, we intervened in the natural cycle of the Lyme disease agent (Borrelia burgdorferi) by immunizing wild white-footed mice (Peromyscus leucopus), a reservoir host species, with either a recombinant antigen of the pathogen, outer surface protein A, or a negative control antigen in a repeated field experiment with paired experimental and control grids stratified by site. Outer surface protein A vaccination significantly reduced the prevalence of B. burgdorferi in nymphal blacklegged ticks (Ixodes scapularis) collected at the sites the following year in both experiments. The magnitude of the vaccine's effect at a given site correlated with the tick infection prevalence found on the control grid, which in turn correlated with mouse density. These data, as well as differences in the population structures of B. burgdorferi in sympatric ticks and mice, indicated that nonmouse hosts contributed more to infecting ticks than previously expected. Thus, where nonmouse hosts play a large role in infection dynamics, vaccination should be directed at additional species.

Linear and circular plasmid content in Borrelia burgdorferi clinical isolates

The genome of Borrelia burgdorferi, the etiologic agent of Lyme disease, is composed of a linear chromosome and more than 20 linear and circular plasmids. Typically, plasmid content analysis has been carried out by pulsed-field gel electrophoresis and confirmed by Southern hybridization. However, multiple plasmids of virtually identical sizes (e.g., lp28 and cp32) complicate the interpretation of such data. The present study was undertaken to investigate the complete plasmid complements of B. burgdorferi clinical isolates cultivated from patients from a single region where early Lyme disease is endemic. A total of 21 isolates obtained from the skin biopsy or blood samples of Lyme disease patients were examined for their complete plasmid complements by Southern hybridization and plasmid-specific PCR analysis. All clinical isolates harbored at least six of the nine previously characterized cp32s. Fourteen isolates harbored all B31-like linear plasmids, and seven isolates simultaneously lacked lp56, lp38, and some segments of lp28-1. The distinctive plasmid profile observed in these seven isolates was specific to organisms that had ribosomal spacer type 2 and pulsed-field gel type A, which implies a clonal origin for this genotype. The presence of nearly identical complements of multiple linear and circular plasmids in all of the human isolates suggests that these plasmids may be particularly necessary for infection, adaptation, and/or maintenance in the infected host.

Detection and molecular typing of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks and in different patient samples from southwest Germany

The prevalence of different genospecies of Borrelia burgdorferi sensu lato in infected ticks could be a determinant for the risk of acquiring Lyme borreliosis (LB) and its clinical presentation. A total of 7373 ticks and 2761 samples from LB patients from the same area in southwest Germany were analyzed by PCR to assess the frequency of the occurrence of LB-associated genospecies. Fifteen percent of the tick samples and 19% of the human samples were found positive for the presence of B. burgdorferi sensu lato. Further identification of 1106 B. burgdorferi sensu lato positive tick samples by reverse line blotting and 125 positive patient samples by nested PCR using species-specific primers revealed the occurrence of B. afzelii, B. burgdorferi sensu stricto, B. garinii and B. valaisiana. Both single-species and mixed infections were noted and a similar distribution of the different genospecies was found in ticks compared with human samples. It was also the purpose of this study to obtain more information about a possible correlation between the distribution of Borrelia species and clinical syndromes of LB. Skin biopsies of 59 patients with acrodermatitis chronica atrophicans and cerebrospinal fluid samples from 78 patients with possible neuroborreliosis were analyzed. In conclusion, the distribution of the different genospecies in ticks is the decisive factor for the occurrence of the different Borrelia genospecies in samples from LB patients. Borrelia afzelii is the predominant genospecies in all kind of samples from the observed area and there seems to be no association of particular Borrelia genospecies with distinct clinical manifestations of LB.

Genetic variability within Borrelia burgdorferi sensu lato genospecies established by PCR-single-strand conformation polymorphism analysis of the rrfA-rrlB intergenic spacer in ixodes ricinus ticks from the Czech Republic

In Europe the Borrelia burgdorferi sensu lato complex is represented by five distinct genospecies: Borrelia burgdorferi sensu stricto, Borrelia afzelii, Borrelia garinii, Borrelia valaisiana, and Borrelia lusitaniae. These taxonomic entities are known to differ in their specific associations with vertebrate hosts and to provoke distinct clinical manifestations in human patients. However, exceptions to these rules have often been observed, indicating that strains belonging to a single genospecies may be more heterogeneous than expected. It is, therefore, important to develop alternative identification tools which are able to distinguish Borrelia strains not only at the specific level but also at the intraspecific level. DNA from a sample of 370 Ixodes ricinus ticks collected in the Czech Republic was analyzed by PCR for the presence of a approximately 230-bp fragment of the rrfA-rrlB intergenic spacer of Borrelia spp. A total of 20.5% of the ticks were found to be positive. The infecting genospecies were identified by analyzing the amplified products by the restriction fragment length polymorphism (RFLP) method with restriction enzyme MseI and by single-strand conformation polymorphism (SSCP) analysis. The two methods were compared, and PCR-SSCP analysis appeared to be a valuable tool for rapid identification of spirochetes at the intraspecific level, particularly when large samples are examined. Furthermore, by using PCR-SSCP analysis we identified a previously unknown Borrelia genotype, genotype I-77, which would have gone unnoticed if RFLP analysis alone had been used.

Disease severity in a murine model of lyme borreliosis is associated with the genotype of the infecting Borrelia burgdorferi sensu stricto strain

The pathogenicity of Borrelia burgdorferi sensu stricto clinical isolates representing 2 distinct ribosomal DNA spacer restriction fragment-length polymorphism genotypes (RSTs) was assessed in a murine model of Lyme disease. B. burgdorferi was recovered from 71.5% and 26.6% of specimens from mice infected with RST1 and RST3 isolates, respectively (P<.0001). The average ankle diameter and histologic scores for carditis and arthritis were significantly higher after 2 weeks of infection among mice infected with RST1 isolates than among those infected with RST3 isolates (P<.001). These clinical manifestations were associated with larger numbers of spirochetes in target tissues but not with the serum sensitivity of the individual isolates. Thus, the development and severity of disease in genetically identical susceptible hosts is determined mainly by the pathogenic properties of the infecting B. burgdorferi isolate. The RST1 genotype is genetically homogeneous and thus may represent a recently evolved clonal lineage that is highly pathogenic in humans and animals.

Asymptomatic Borrelia burgdorferi infection

Little is known about the natural history of asymptomatic Borrelia burgdorferi infection. Our analysis of the asymptomatic infections diagnosed serologically in a recent OspA vaccine trial conducted in the United States (N Engl J Med 1998;339: 209-215), suggests that the natural history of this event is more benign than that reported for untreated patients with erythema migrans (Ann Intern Med 1987;107: 725-731). We hypothesize that this is due either to incorrect diagnosis since the specificity of the serologic criteria used to diagnose asymptomatic infection in the vaccine study is unknown, or to infection with non-pathogenic strains of B. burgdorferi. Increasing evidence indicates that the invasive potential of strains of B. burgdorferi varies according to the specific subtype. Theoretically, a serologic testing method could be devised which would distinguish infection with invasive versus non-invasive strains of B. burgdorferi, and allow testing of the second hypothesis.