Treponema pallidum PCR with blood and cerebrospinal fluid of newborns exposed and not exposed to syphilis during pregnancy.

INTRODUCTION: Congenital syphilis (CS) has severe adverse outcomes, including abortion and death. Diagnosis of CS in asymptomatic newborns remains difficult. This study aims to evaluate an in-house polymerase chain reaction (PCR) on cerebrospinal fluid (CSF) and blood samples (BS) to identify T. pallidum DNA in newborns. METHODOLOGY: We performed an exploratory cross-sectional study that included newborns exposed to syphilis during pregnancy (SEG) and non-exposed (SNEG) newborns, between 2019 and 2020. In-house conventional PCR for T. pallidum targeting the tpp47 gene was used to analyze CSFS and dried blood spots. RESULTS: BS was obtained from 54 newborns (33 SEG/21 SNEG) and CSF from 55 newborns (33 SEG/22 SNEG). Twenty-five (71.4%) SEG newborns had reactive BS rapid plasmatic reagins (RPR), and all of them had RPR titers less than or equal to the corresponding maternal titers. All RPR CSF tests were negative. PCR for T. pallidum DNA was positive in 19/33 (57.6%) BS, and in 22/33 CSF. The only SEG newborn with clinical signs of early CS had a positive CSF PCR and a negative BS PCR. Conversely, among SNEG newborns, PCR was positive in 2/21 BS and 5/22 (22.7%) CSF. CONCLUSIONS: T. pallidum DNA was identified using our PCR tests. The exposed group did not present abnormalities that would indicate CS. This prevented conclusions regarding sensitivity and specificity. Dried spot permitted bedside collection, easy transportation, and storage. Further research is needed to evaluate and improve the accuracy of CS low-cost PCR tests, especially for limited resource settings.

ADAMTS5 Promotes Permeability of the Blood-Brain Barrier during Treponema pallidum Subspecies pallidum Invading the Central Nervous System.

The pathogenesis of neurosyphilis remains unclear. A previous study found a noteworthy up-regulation of a disintegrin and metalloproteinase with thrombospondin type 1 motif 5 (ADAMTS5) gene in human brain microvascular endothelial cells cocultured with Treponema pallidum subspecies pallidum (Tp). To investigate the ADAMTS5 role in Tp invading the central nervous system (CNS), we conducted relevant experiments. Our study revealed that Tp caused an increase in human cortical microvascular endothelial cell/D3 (hCMEC/D3) barrier permeability and significantly enhanced ADAMTS5 expression. The heightened permeability of the hCMEC/D3 barrier was effectively mitigated by inhibiting ADAMTS5. During this process, Tp promoted interleukin-1ß production, which, in turn, facilitated ADAMTS5 expression. Furthermore, Tp significantly reduced the glycocalyx on the surface of hCMEC/D3 cells, which was also ameliorated by inhibiting ADAMTS5. Additionally, ADAMTS5 and endothelial glycocalyx components notably increased in the cerebrospinal fluid of HIV-negative neurosyphilis patients. This research provided the first demonstration of the ADAMTS5 role in Tp invading the CNS and offered new insight into neurosyphilis pathogenesis.

Establishment of reference measurement procedure and reference material for Treponema pallidum.

Stem cell preparations, as a new type of biotherapeutic product, should be subject to strict quality control in terms of cell safety. The testing of stem cell donors and blood products used in stem cell cultures, including but not limited to Treponema pallidum, is needed to reduce the risk of transmission of infectious diseases by stem cell medical products. In this study, a reference measurement procedure (RMP) was established based on digital PCR (dPCR). A homogeneous reference material (RM) of TP containing the tpp47 gene has been developed and characterized. Two dPCR assays (A and B) show ideal linearity within five orders of magnitude. The limit of quantification (LoQ) for both assays is 57 copies/reaction; the limits of detection (LoD) are 9.69 and 9.59 copies/reaction, respectively. The quantitative results of the established duplex dPCR assay are in good agreement. The RM of TP containing the tpp47 gene has been developed and characterized. The reference value with its expanded uncertainty is (2.21 ± 0.22) × 106 copies per µL determined by the established dPCR RMP. The developed dPCR was validated by applying a simulated stem cell matrix, and no impact was observed on the accuracy of dPCR. By providing an accurate reference value for the absolute copy number of the target gene, the developed RM can be used to improve the reliability of TP testing in the production of stem cell preparations and clinical diagnostics.

Redefining the treponemal history through pre-Columbian genomes from Brazil.

The origins of treponemal diseases have long remained unknown, especially considering the sudden onset of the first syphilis epidemic in the late 15th century in Europe and its hypothesized arrival from the Americas with Columbus' expeditions1,2. Recently, ancient DNA evidence has revealed various treponemal infections circulating in early modern Europe and colonial-era Mexico3-6. However, there has been to our knowledge no genomic evidence of treponematosis recovered from either the Americas or the Old World that can be reliably dated to the time before the first trans-Atlantic contacts. Here, we present treponemal genomes from nearly 2,000-year-old human remains from Brazil. We reconstruct four ancient genomes of a prehistoric treponemal pathogen, most closely related to the bejel-causing agent Treponema pallidum endemicum. Contradicting the modern day geographical niche of bejel in the arid regions of the world, the results call into question the previous palaeopathological characterization of treponeme subspecies and showcase their adaptive potential. A high-coverage genome is used to improve molecular clock date estimations, placing the divergence of modern T. pallidum subspecies firmly in pre-Columbian times. Overall, our study demonstrates the opportunities within archaeogenetics to uncover key events in pathogen evolution and emergence, paving the way to new hypotheses on the origin and spread of treponematoses.

Low genetic diversity of Treponema pallidum ssp. pertenue (TPE) isolated from patients' ulcers in Namatanai District of Papua New Guinea: Local human population is infected by three TPE genotypes.

Yaws is an endemic disease caused by Treponema pallidum subsp. pertenue (TPE) that primarily affects children in rural regions of the tropics. The endemic character of yaws infections and the expected exclusive reservoir of TPE in humans opened a new opportunity to start a yaws eradication campaign. We have developed a multi-locus sequence typing (MLST) scheme for TPE isolates combining the previously published (TP0548, TP0488) and new (TP0858) chromosomal loci, and we compared this typing scheme to the two previously published MLST schemes. We applied this scheme to TPE-containing clinical isolates obtained during a mass drug administration study performed in the Namatanai District of Papua New Guinea between June 2018 and December 2019. Of 1081 samples collected, 302 (28.5%) tested positive for TPE DNA, from which 255 (84.4%) were fully typed. The TPE PCR-positivity in swab samples was higher in younger patients, patients with single ulcers, first ulcer episodes, and with ulcer duration less than six months. Non-treponemal serological test positivity correlated better with PCR positivity compared to treponema-specific serological tests. The MLST revealed a low level of genetic diversity among infecting TPE isolates, represented by just three distinct genotypes (JE11, SE22, and TE13). Two previously used typing schemes revealed similar typing resolutions. Two new alleles (one in TP0858 and one in TP0136) were shown to arise by intragenomic recombination/deletion events. Compared to samples genotyped as JE11, the minor genotypes (TE13 and SE22) were more frequently detected in samples from patients with two or more ulcers and patients with higher values of specific TP serological tests. Moreover, the A2058G mutation in the 23S rRNA genes of three JE11 isolates was found, resulting in azithromycin resistance.

A Cluster of Ocular Syphilis Cases with a Common Sex Partner - Southwest Michigan, 2022.

Untreated syphilis can lead to ocular syphilis, otosyphilis, and neurosyphilis, conditions resulting from Treponema pallidum infection of the eye, inner ear, or central nervous system. During March-July 2022, Michigan public health officials identified a cluster of ocular syphilis cases. The public health response included case investigation, partner notification, dissemination of health alerts, patient referral to a public health clinic for diagnosis and treatment, hospital care coordination, and specimen collection for T. pallidum molecular typing. Five cases occurred among southwest Michigan women, all of whom had the same male sex partner. The women were aged 40-60 years, HIV-negative, and identified as non-Hispanic White race; the disease was staged as early syphilis, and all patients were hospitalized and treated with intravenous penicillin. The common male sex partner was determined to have early latent syphilis and never developed ocular syphilis. No additional transmission was identified after the common male partner's treatment. Due to lack of genetic material in limited specimens, syphilis molecular typing was not possible. A common heterosexual partner in an ocular syphilis cluster has not been previously documented and suggests that an unidentified strain of T. pallidum might have been associated with increased risk for systemic manifestations of syphilis. A high index of clinical suspicion and thorough sexual history are critical to diagnosing ocular syphilis, otosyphilis, and neurosyphilis. Coordination of disease surveillance with disease intervention specialist investigation and treatment referral can interrupt syphilis transmission.

Insight into the invasion process and immune-protective evaluation of Tp0971, a membrane lipoprotein from Treponema pallidum.

IMPORTANCE: The past two decades have seen a worldwide resurgence in infections caused by Treponema pallidum (T. pallidum) subsp. pallidum, the syphilis spirochete. The well-recognized capacity of the syphilis spirochete for early dissemination and immune evasion has earned it the designation "the stealth pathogen." There are many hurdles to studying syphilis pathogenesis, most notably the difficulty of culturing and genetically manipulating T. pallidum, as well as the absence of an effective vaccine for T. pallidum prevention. T. pallidum infection in humans is a complex and lengthy process. In this study, we investigated the invasion process and the function of the infection-dependent antigen Tp0971 as an immunogen to inhibit the dissemination of T. pallidum in an animal infection model. This enables a better understanding of the specific pathogenic mechanism of this pathogen, syphilis pathogenesis, and vaccine research.

Deep proteome coverage advances knowledge of Treponema pallidum protein expression profiles during infection.

Comprehensive proteome-wide analysis of the syphilis spirochete, Treponema pallidum ssp. pallidum, is technically challenging due to high sample complexity, difficulties with obtaining sufficient quantities of bacteria for analysis, and the inherent fragility of the T. pallidum cell envelope which further complicates proteomic identification of rare T. pallidum outer membrane proteins (OMPs). The main aim of the present study was to gain a deeper understanding of the T. pallidum global proteome expression profile under infection conditions. This will corroborate and extend genome annotations, identify protein modifications that are unable to be predicted at the genomic or transcriptomic levels, and provide a foundational knowledge of the T. pallidum protein expression repertoire. Here we describe the optimization of a T. pallidum-specific sample preparation workflow and mass spectrometry-based proteomics pipeline which allowed for the detection of 77% of the T. pallidum protein repertoire under infection conditions. When combined with prior studies, this brings the overall coverage of the T. pallidum proteome to almost 90%. These investigations identified 27 known/predicted OMPs, including potential vaccine candidates, and detected expression of 11 potential OMPs under infection conditions for the first time. The optimized pipeline provides a robust and reproducible workflow for investigating T. pallidum protein expression during infection. Importantly, the combined results provide the deepest coverage of the T. pallidum proteome to date.

Dendritic Cell-Derived Exosomes Stimulated by Treponema pallidum Induce Endothelial Cell Inflammatory Response through the TLR4/MyD88/NF-κB Signaling Pathway.

Exosomes have been implicated in vascular damage in recent research. The influence of dendritic cell-derived exosomes generated by Treponema pallidum (T. pallidum) on the inflammatory process of vascular cells was examined in this study. Human umbilical vein endothelial cells (HUVECs) were cocultured with exosomes isolated from dendritic cells induced by T. pallidum. Western blot and reverse transcription-quantitative real-time polymerase chain reaction were used to assess toll-like receptor 4 (TLR4) expression and the quantity of proinflammatory cytokines. The findings showed that the expression of TLR4 was considerably upregulated, and TLR4 knockdown dramatically reduced interleukin-1ß (IL-1ß), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) production in exosome-treated HUVECs. Furthermore, TLR4 silencing reduced myeloid differentiation primary response protein 88 (MyD88) and nuclear factor kappa light chain enhancer of activated B cells (NF-κB) levels in exosome-treated HUVECs. Additionally, suppression of the activity of NF-κB with BAY11-7082, an NF-κB inhibitor, also reduced the exosome-treated inflammatory response. Our results suggested that dendritic cell-derived exosomes stimulated by T. pallidum induced endothelial cell inflammation, and the TLR4/MyD88/NF-κB signal axis was activated, significantly increasing IL-1ß, IL-6, and TNF-α expression. This may have a significant role in the vascular inflammatory response in syphilis, which would contribute to the understanding of the pathogenesis of syphilis and the host immunological response to T. pallidum.

Antimicrobial susceptibility of Treponema pallidum subspecies pallidum: an in-vitro study.

BACKGROUND: The increasing incidence of syphilis and the limitations of first-line treatment with penicillin, particularly in neurosyphilis, neonatal syphilis, and pregnancy, highlight the need to expand the therapeutic repertoire for effective management of this disease. We assessed the in-vitro efficacy of 18 antibiotics from several classes on Treponema pallidum subspecies pallidum (T pallidum), the syphilis bacteria. METHODS: Using the in-vitro culture system for T pallidum, we exposed the pathogen to a concentration range of each tested antibiotic. After a 7-day incubation, the treponemal burden was evaluated by quantitative PCR targeting the T pallidum tp0574 gene. The primary outcome was the minimum inhibitory concentration (MIC) at which the quantitative PCR values were not significantly higher than the inoculum wells. We also investigated the susceptibility of macrolide-resistant strains to high concentrations of azithromycin, and the possibility of developing resistance to linezolid, a proposed candidate for syphilis treatment. FINDINGS: Amoxicillin, ceftriaxone, several oral cephalosporins, tedizolid, and dalbavancin exhibited anti-treponemal activity at concentrations achievable in human plasma following regular dosing regimens. The experiments revealed a MIC for amoxicillin at 0·02 mg/L, ceftriaxone at 0·0025 mg/L, cephalexin at 0·25 mg/L, cefetamet and cefixime at 0·0313 mg/L, cefuroxime at 0·0156 mg/L, tedizolid at 0·0625 mg/L, spectinomycin at 0·1 mg/L, and dalbavancin at 0·125 mg/L. The MIC for zoliflodacin and balofloxacin was 2 mg/L. Ertapenem, isoniazid, pyrazinamide, and metronidazole had either a poor or no effect. Azithromycin concentrations up to 2 mg/L (64 times the MIC) were ineffective against strains carrying mutations associated to macrolide resistance. Exposure to subtherapeutic doses of linezolid for 10 weeks did not induce phenotypic or genotypic resistance. INTERPRETATION: Cephalosporins and oxazolidinones are potential candidates for expanding the current therapeutic repertoire for syphilis. Our findings warrant testing efficacy in animal models and, if successful, clinical assessment of efficacy. FUNDING: European Research Council.

Placental Syphilis: A Comprehensive Review of Routine Histomorphology, HIV Co-infection, Penicillin Treatment, Immunohistochemistry, and Polymerase Chain Reaction.

Introduction: Placental examination is valuable for diagnosing congenital syphilis, but the classic histological triad is not always observed. This study aimed to identify additional morphological clues, evaluate the sensitivity of IHC and qPCR, and investigate the impact of HIV co-infection and penicillin treatment on placental morphology. Materials and methods: Two hundred and fifteen placental specimens with treponemal infection were reviewed. Morphological findings, IHC, and qPCR results were analyzed. Results: Chronic villitis (94%), acute chorioamnionitis (91.6%), and villous immaturity (65.6%) were the most common abnormalities. HIV co-infection and penicillin treatment were associated with reduced frequencies of inflammatory lesions. IHC and qPCR exhibited sensitivities of 74.4 and 25.8%, respectively, confirming the diagnosis in 42 cases with negative or unknown serology. Conclusion: Villitis, chorioamnionitis, and villous immaturity were identified as the predominant placental abnormalities. HIV co-infection and penicillin treatment can impact morphology and hamper the diagnosis. IHC and q-PCR are valuable adjuncts when serology is negative.

The outer membrane protein Tp92 of Treponema pallidum delays human neutrophil apoptosis via the ERK, PI3K/Akt, and NF-κB pathways.

Syphilis is a persistent sexually transmitted disease caused by infiltration of the elusive pathogen Treponema pallidum. Despite the prevalence of human polymorphonuclear neutrophils (hPMNs) within cutaneous lesions, which are characteristic of incipient syphilis, their role in T. pallidum infection remains unclear. Tp92 is the only T. pallidum helical outer membrane protein that exhibits structural features similar to those of outer membrane proteins in other gram-negative bacteria. However, the functional mechanism of this protein in immune cells remains unclear. Neutrophils are short-lived cells that undergo innate apoptosis in response to external stimuli that typically influence this process. In this study, we determined that Tp92 impedes the activation of procaspase-3 via the ERK MAPK, PI3K/Akt, and NF-κB signaling pathways, consequently suppressing caspase-3 activity within hPMNs, and thereby preventing hPMNs apoptosis. Furthermore, Tp92 could also modulate hPMNs apoptosis by enhancing the expression of the anti-apoptotic protein Mcl-1, stimulating IL-8 secretion, and preserving the mitochondrial membrane potential. These findings provide valuable insights into the molecular mechanisms underlying T. pallidum infection and suggest potential therapeutic targets for syphilis treatment.

Advancements in the development of nucleic acid vaccines for syphilis prevention and control.

Syphilis, a chronic systemic sexually transmitted disease, is caused by the bacterium Treponema pallidum (T. pallidum). Currently, syphilis remains a widespread infectious disease with significant disease burden in many countries. Despite the absence of identified penicillin-resistant strains, challenges in syphilis treatment persist due to penicillin allergies, supply issues, and the emergence of macrolide-resistant strains. Vaccines represent the most cost-effective strategy to prevent and control the syphilis epidemic. In light of the ongoing global coronavirus disease 2019 (COVID-19) pandemic, nucleic acid vaccines have gained prominence in the field of vaccine research and development, owing to their superior efficiency compared to traditional vaccines. This review summarizes the current state of the syphilis epidemic and the preliminary findings in T. pallidum nucleic acid vaccine research, discusses the challenges associated with the development of T. pallidum nucleic acid vaccines, and proposes strategies and measures for future T. pallidum vaccine development.

Treponema pallidum promoted microglia apoptosis and prevented itself from clearing by human microglia via blocking autophagic flux.

Treponema pallidum (Tp) has a well-known ability to evade the immune system and can cause neurosyphilis by invading the central nervous system (CNS). Microglia are resident macrophages of the CNS that are essential for host defense against pathogens, this study aims to investigate the interaction between Tp and microglia and the potential mechanism. Here, we found that Tp can exert significant toxic effects on microglia in vivo in Tg (mpeg1: EGFP) transgenic zebrafish embryos. Single-cell RNA sequencing results showed that Tp downregulated autophagy-related genes in human HMC3 microglial cells, which is negatively associated with apoptotic gene expression. Biochemical and cell biology assays further established that Tp inhibits microglial autophagy by interfering with the autophagosome-lysosome fusion process. Transcription factor EB (TFEB) is a master regulator of lysosome biogenesis, Tp activates the mechanistic target of rapamycin complex 1 (mTORC1) signaling to inhibit the nuclear translocation of TFEB, leading to decreased lysosomal biogenesis and accumulated autophagosome. Importantly, the inhibition of autophagosome formation reversed Tp-induced apoptosis and promoted microglial clearance of Tp. Taken together, these findings show that Tp blocks autophagic flux by inhibiting TFEB-mediated lysosomal biosynthesis in human microglia. Autophagosome accumulation was demonstrated to be a key mechanism underlying the effects of Tp in promoting apoptosis and preventing itself from clearing by human microglia. This study offers novel perspectives on the potential mechanism of immune evasion employed by Tp within CNS. The results not only establish the pivotal role of autophagy dysregulation in the detrimental effects of Tp on microglial cells but also bear considerable implications for the development of therapeutic strategies against Tp, specifically involving mTORC1 inhibitors and autophagosome formation inhibitors, in the context of neurosyphilis patients.

Timely Diagnosis of Incubating Syphilis Infections Using Treponema pallidum Transcription-Mediated Amplification Assay.

BACKGROUND: Syphilis is a complex, multistage, sexually transmitted infection (STI) caused by the bacterium Treponema pallidum subspecies pallidum (TP). New diagnostic tools are needed to minimize transmission. In this study, we aimed to assess the additional value of an investigational transcription-mediated amplification test for TP (TP-TMA) for routine diagnostics. METHODS: Between September 2021 and August 2022, visits by all participants of the national preexposure prophylaxis (PrEP) program at the sexual health center (SHC) in Amsterdam were included. Anal, pharyngeal, vaginal, and urine samples collected for Chlamydia trachomatis and Neisseria gonorrhoeae screening were additionally tested with the TP-TMA assay based on detection of 23S rRNA of TP. RESULTS: In total, 9974 SHC visits by 3283 participants were included. There were 191 infectious syphilis cases diagnosed: 26 (14%) primary syphilis, 54 (29%) secondary syphilis, and 111 (58%) early latent syphilis. In 79 of the 191 (41%) syphilis cases, at least 1 sample was TP-TMA-positive. For 16 participants, the positive TP-TMA result was not concordant with routine diagnostics. Of those, 2 participants were treated for syphilis within a week before the visit. Eight participants were treated for a syphilis notification at the visit or for another STI. Five participants were diagnosed with syphilis at the following visit, and 1 participant was lost to follow-up. CONCLUSIONS: By adding the TP-TMA assay to routine diagnostics, we identified 14 of 191 (7%) additional syphilis infections among participants of the national PrEP program. The TP-TMA assay is a useful diagnostic tool to increase syphilis case finding and thus limit the transmission of syphilis.

Rapid Serologic Test for Diagnosis of Yaws in Patients with Suspicious Skin Ulcers.

The Chembio DPP (Dual Path Platform) Syphilis Screen & Confirm kit (https://chembio.com) is a rapid serologic test that can be used to diagnose yaws. We evaluated its capacity to detect patients with ulcers that tested PCR positive for Treponema pallidum subsp. pertenue. DPP detected 84% of ulcers that were positive by PCR.

Old World Medieval Treponema pallidum Complex Treponematosis: A Case Report.

BACKGROUND: Introduction of 1 Treponema pallidum complex pathogen in naive European populations following the return of Christopher Columbus' troops from Central America in 1493 is a central dogma in venereology. METHODS: Among skeletal elements from the seventh or eighth century uncovered in Roquevaire, France, individual RS-1003 femur macroscopically suspected of having an infectious disease was investigated by means of paleoautoimmunohistochemistry, direct metagenomics, and paleoserology, along with 1 control femur from an apparently healthy individual (R-1003) and experimental negative controls. RESULTS: RS-1003 femur showed infectious bone; paleoautoimmunohistochemistry of the lesions led to microscopic detection of a T. pallidum complex pathogen. Phylogenetic analyses comprising 71 T. pallidum complex-specific reads covering 2.37% of the T. pallidum subsp. pallidum reference genome sequence revealed an ancestral T. pallidum complex pathogen in the lesion. Paleoserology detecting T. pallidum-specific antigens confirmed positive serological findings in individual RS-1003. Individual R-1003 and the negative controls remained negative. CONCLUSIONS: This case, predating by 8 centuries previous detections of T. pallidum complex treponematosis in Europe, indicated that European populations were not naive to these pathogens before the 1493 introduction of a Central American T. pallidum complex pathogen overwhelming the T. pallidum ones previously circulating in the Old World. These data break a century-old dogma in medical microbiology.

The Role of Decorin in the Adhesion Process of Treponema Pallidum Subspecies Pallidum to Human Brain Microvascular Endothelial Cells.

Objective: This study aims to investigate the role of decorin in the adhesion process of Treponema pallidum subspecies pallidum (T. pallidum) to human brain microvascular endothelial cells. Methods: The study involved an in vitro experimental design. Western blot analysis was conducted to determine the protein expression level of decorin in the cells. The cells were divided into four groups: Tp group, inactivated Tp group, LPS group, and negative control group. The adhesion of T. pallidum to the cells was analyzed using darkfield microscopy counting and quantitative polymerase chain reaction (qPCR). The cells were divided into four groups based on different preprocessing treatments: control group, decorin group, DCN-siRNA group, and DCN-siRNA+decorin group. Changes in the F-actin of the cells were explored using confocal laser scanning microscopy. The cells were divided into the Tp group, Tp+decorin group, and control group. Results: Western blot analysis showed high expression of decorin in the Tp group and LPS group. Darkfield microscopy counting revealed a significantly higher number of T. pallidum adhered to a single cell in the decorin group compared to the control group. Conversely, the number of adhered T. pallidum was significantly lower in the DCN-siRNA group compared to the control group. qPCR results indicated a considerably higher T. pallidum load in the decorin group compared to the control group. In the Tp group, T. pallidum treatment induced the reorganization of F-actin, while the distribution of F-actin in the Tp+decorin group was comparable to that of the control group. Conclusions: Decorin enhances the adhesion of T. pallidum to human brain microvascular endothelial cells, suggesting that decorin may act as one of the receptors regulating the adhesion of T. pallidum to cells. Furthermore, T. pallidum treatment triggers the rearrangement of F-actin in cells, and decorin plays a protective role in this process.

Longitudinal Variations in the tprK Gene of Treponema pallidum in an Amoy Strain-Infected Rabbit Model.

Heterogeneous tprK sequences have been hypothesized to be an important factor for persistent infection of Treponema pallidum subsp. pallidum (T. pallidum) in humans. Previous research has only explored tprK diversity using a rabbit model infected with almost clonal isolates, which is inconsistent with the fact that infected human isolates contain multiple heterogeneous tprK sequences. Here, we used the T. pallidum Amoy strain with heterogeneous tprK sequences to establish a rabbit infection model and explore longitudinal variations in the tprK gene under normal infection, immunosuppression treatment, and benzathine penicillin G (BPG) treatment using next-generation sequencing. The diversity of the tprK gene was high in all three groups but was highest in the control group and lowest in the BPG group. Interestingly, the overall diversity of tprK in all three groups decreased during infection, exhibiting a "more to less" trend, indicating that survival selection may be an important factor affecting tprK variation in the later infection stage. BPG treatment appeared to reduce the diversity of tprK but increased the frequency of predominant sequence changes, which might facilitate the escape of T. pallidum from the host immune clearance. Furthermore, the original predominant V region sequence did not disappear with disease progression but retained a relatively high proportion within the population, suggesting a new direction for tprK-related vaccine research. This study provides insights into longitudinal variations within the highly heterogeneous tprK gene sequences of T. pallidum and will contribute to further exploration of the pathogenesis of syphilis. IMPORTANCE The tprK variations are an important factor in persistent T. pallidum infection. A nearly clonal isolate has been used previously to investigate the mechanism of tprK gene variations; however, clinical T. pallidum isolates in infected humans exhibit multiple heterogeneous tprK sequences. Here, we use next-generation sequencing to explore longitudinal variations in the tprK gene under normal infection and immunosuppression and benzathine penicillin G treatment in a rabbit model infected with the Amoy strain with heterogeneous tprK sequences. The overall diversity of tprK in all three groups was high and decreased during infection, exhibiting a "more to less" trend. Benzathine penicillin G treatment reduced the diversity of tprK but increased the frequency of predominant sequence changes. Moreover, the original predominant V region sequence did not disappear as the disease progressed but remained at a relatively high proportion within the population. The research results give us a new understanding about tprK variation.