Adaptation of Borrelia burgdorferi in the tick and the mammalian host

Borrelia burgdorferi, the causative agent of Lyme disease, shows a great ability to adapt to different environments, including the arthropod vector, and the mammalian host. The success of these microorganisms to survive in nature and complete their enzootic cycle depends on the regulation of genes that are essential to their survival in the different environments. This review describes the current knowledge of gene expression by B. burgdorferi in the tick and the mammalian host. The functions of the differentially regulated gene products as well as the factors that influence their expression are discussed. A thorough understanding of the changes in gene expression and the function of the differentially expressed antigens during the life cycle of the spirochete will allow a better control of this prevalent infection and the design of new, second generation vaccines to prevent infection with the spirochete.     

Feeding of Ticks on Animals for Transmission and Xenodiagnosis in Lyme Disease Research

Transmission of the etiologic agent of Lyme disease, Borrelia burgdorferi, occurs by the attachment and blood feeding of Ixodes species ticks on mammalian hosts. In nature, this zoonotic bacterial pathogen may use a variety of reservoir hosts, but the white-footed mouse (Peromyscus leucopus) is the primary reservoir for larval and nymphal ticks in North America. Humans are incidental hosts most frequently infected with B. burgdorferi by the bite of ticks in the nymphal stage. B. burgdorferi adapts to its hosts throughout the enzootic cycle, so the ability to explore the functions of these spirochetes and their effects on mammalian hosts requires the use of tick feeding. In addition, the technique of xenodiagnosis (using the natural vector for detection and recovery of an infectious agent) has been useful in studies of cryptic infection. In order to obtain nymphal ticks that harbor B. burgdorferi, ticks are fed live spirochetes in culture through capillary tubes. Two animal models, mice and nonhuman primates, are most commonly used for Lyme disease studies involving tick feeding. We demonstrate the methods by which these ticks can be fed upon, and recovered from animals for either infection or xenodiagnosis.     

Borrelia Burgdorferi Upregulates the Adhesion Molecules E-selectin,P-selectin,ICAM-1 and VCAM-1 on Mouse Endothelioma Cells in vitro

In order to obtain more information on processes leading to Borrelia burgdorferi-induced inflammation in the host, we have developed an in vitro model to study the upregulation of cell surface expression of adhesion molecules on endothelial cells by spirochetes. A mouse endothelioma cell line, derived from brain capillaries, bEnd3, was used as indicator population. bEnd3 cells were incubated with preparations of viable, inactivated or sonicated spirochetes and the expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 was monitored by immunocytochemistry and quantified by cell surface ELISA. We show that all three spirochetal preparations are able to upregulate cell surface expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 on bEnd3 cells in a dose-dependent manner. The kinetics of cell surface expression of the individual adhesion molecules in the presence of Borrelia burgdorferi showed maxima at about 50 h of incubation or later; this was distinct from results obtained with sonicated-preparations of Escherichia coli bacteria or with enterobacterial LPS where peak expression was observed between 4 h and 16 h. The fact that Borrelia burgdorferi does not contain conventional LPS suggests that the mode of induction of adhesion molecules on endothelial cells is influenced by the phenotype of bacteria. At the peak of spirochete-induced cell surface expression of adhesion molecules (≈50 h), bEnd3 cells were found to bind cells of a VLA-4⁺ B lymphoma line (L1-2) much more efficiently than untreated control cells. The binding of L1-2 cells to presensitized bEnd3 cells was significantly inhibited (more than 75%) in the presence of monoclonal antibodies to both VLA-4 and its endothelial counterreceptor VCAM-1. These findings demonstrate that Borrelia burgdorferi organisms are able to induce functionally active adhesion molecules on endothelial cells in vitro and suggest that E-selectin, P-selectin, ICAM-1 and VCAM-1 play an important role in the pathogenesis of spirochetal infection.     

The Lon-2 protease of Borrelia burgdorferi is critical for infection in the mammalian host

Borrelia burgdorferi encodes a functional homolog of canonical Lon protease termed Lon-2. To date, the contribution of Lon-2 to B. burgdorferi fitness and infection remains unexplored. Herein, we showed that expression of lon-2 was highly induced during animal infection, suggesting that Lon-2 is important for B. burgdorferi infection. We further generated a lon-2 deletion mutant. Compared with that of wild-type (WT) strain, the infectivity of the mutant was severely attenuated in a murine infection model. Although no growth defect was observed for the mutant in normal BSK-II medium, resistance of the lon-2 mutant to osmotic stress was markedly reduced. In addition, when exposed to tert-Butyl hydroperoxide, survival of the lon-2 mutant was impaired. In addition, we found that the protein levels of RpoS and RpoS-dependent OspC were decreased in the mutant. All these phenotypes were restored to WT or near-WT levels when lon-2 mutation was complemented in cis. Taken together, these results demonstrate that Lon-2 is critical for B. burgdorferi to establish infection and to cope with environmental stresses. This study provides a foundation for further uncovering the direct link between the dual roles of Lon-2 in protein quality control and bacterial pathogenesis.     

Landscape features predict the current and forecast the future geographic spread of Lyme disease

Lyme disease, the most prevalent vector-borne disease in North America, is increasing in incidence and geographic distribution as the tick vector, Ixodes scapularis, spreads to new regions. We re-construct the spatial-temporal invasion of the tick and human disease in the Midwestern US, a major focus of Lyme disease transmission, from 1967 to 2018, to analyse the influence of spatial factors on the geographic spread. A regression model indicates that three spatial factors—proximity to a previously invaded county, forest cover and adjacency to a river—collectively predict tick occurrence. Validation of the predictive capability of this model correctly predicts counties invaded or uninvaded with 90.6% and 98.5% accuracy, respectively. Reported incidence increases in counties after the first report of the tick; based on this modelled relationship, we identify 31 counties where we suspect I. scapularis already occurs yet remains undetected. Finally, we apply the model to forecast tick establishment by 2021 and predict 42 additional counties where I. scapularis will probably be detected based upon historical drivers of geographic spread. Our findings leverage resources dedicated to tick and human disease reporting and provide the opportunity to take proactive steps (e.g. educational efforts) to prevent and limit transmission in areas of future geographic spread.     

Tick abundances in South London parks and the potential risk for Lyme borreliosis to the general public

Tick abundances and prevalences of infection with Borrelia burgdorferi sensu lato, the causative agent of Lyme disease, were investigated in four South London parks. A total of 360 transects were sampled using three methods of collection (blanket, leggings and flags) simultaneously. No ticks were found on Wimbledon Common or at Hampton Court, but 1118 Ixodes ricinus (Ixodida: Ixodidae) ticks were collected at Richmond and Bushy Parks. At Richmond Park, lower canopy humidity [odds ratio (OR) 0.94; P = 0.005], increased mat depth (OR 1.15; P < 0.001) and increased soil moisture (OR 1.40; P = 0.001) predicted the presence of I. ricinus, and increased sward height [incidence rate ratio (IRR) 1.01; P = 0.006] and decreased ground temperature (IRR 0.90; P = 0.009) predicted increased abundance. At Bushy Park, thicker mat depth predicted tick presence (OR 1.17; P = 0.006) and increasing temperature correlated with tick absence (OR 0.57; P = 0.023). A total of 279 ticks were screened for the presence of B. burgdorferi using quantitative polymerase chain reaction. Point prevalences of 0% for larvae (n = 78), 2.14% for nymphs (n = 174) and 0% for adult ticks (n = 7) related to an acarological risk of 0.22 infected ticks per 40 m transect in Richmond Park. The abundance of ticks and the acarological risk, particularly at Richmond Park, highlight the need for appropriate communication of the associated risk to the general public frequenting these recreational areas.     

Expression and secretion of outer surface protein (OSP-A) of Borrelia burgdorferi from Escherichia coli

Abstract Outer surface protein A (OspA) is encoded by the ospA gene from Borrelia burgdorferi . This protein induces immunity against infection in mice. The cloning and expression of OspA in Escherichia coli have been previously described, but the secretion of OspA into culture media in E. coli has not yet been reported. In this report we demonstrate that a chimeric OspA protein was secreted into culture media by E. coli when it also harbors the hemolysin secretion genes hlyBD . The OspA fusion protein was also overexpressed from a T7 promoter and purified by immobilized metal ion chromatography. This was possible because the fusion protein contains ix histidyl residues in its N-terminus.     

Relationship between infectivity and OspC expression in Lyme disease Borrelia

Abstract Borrelia burgdorferi sensu stricto strain 297 and B. garinii strains HP1 and 12–92 were serially subcultured for 36–50 passages in vitro for 1 year. All low-passage strains showed abundant expression of outer surface protein C (OspC) in the 22–23-kDa range, but the high-passage strains lost or showed reduced expression of OspC in comparison with the low-passage strains. The low-passage strains efficiently infected outbred ddY mice when inoculated into the hind footpad or peritoneal cavity. In contrast, the incidence of infection with the high-passage strains was low. Isolates from the bladders of mice inoculated with the high-passage strains expressed large amounts of OspC in comparison with those originally inoculated. These results indicate that OspC expression is related to the infectivity of Lyme disease borreliae.     

Evidence for frequent OspC gene transfer between Borrelia valaisiana sp. nov. and other Lyme disease spirochetes

IMP-1 metallo-beta-lactamase is a transferable carbapenem-hydrolyzing enzyme found in some clinical isolates of Pseudomonas aeruginosa, Serratia marcescens and Klebsiella pneumoniae. Bacteria that express IMP-1 show significantly reduced sensitivity to carbapenems and other beta-lactam antibiotics. A series of thioester derivatives has been shown to competitively inhibit purified IMP-1. As substrates for IMP-1, the thioesters yielded thiol hydrolysis products which themselves were reversible competitive inhibitors. The thioesters also increased sensitivity to the carbapenem L-742,728 in an IMP-1-producing laboratory stain of Escherichia coli, but will need further modification to improve their activity in less permeable organisms such as Pseudomonas and Serratia. Nonetheless, the thioester IMP-1 inhibitors offer an encouraging start to overcoming metallo-beta-lactamase-mediated resistance in bacteria.     

Restriction endonuclease analysis of four Borrelia burgdorferi strains

Abstract A restriction endonuclease analysis was performed on four strains of Borrelia burgdorferi : one isolated from man (SF), one from Ixodes dammini (B31) and two form I. ricinus (BITS in Italy and B45 in Germany). Digestion by Taq I and Hae III gave the best resolution of the DNA fragments. Three different restriction patterns were obtained: BITS and B45 showed only one band difference. These results correlate with the reactivity of the four strains with monoclonal antibodies.