Identification and purification of a recombinant Treponema pallidum basic membrane protein antigen expressed in Escherichia coli

Assessment of recombinant antigens Tp0100 and Tp1016 of Treponema pallidum for serological diagnosis of syphilis

Objective

To discover novel serodiagnostic candidates for the serological diagnosis of syphilis.

Methods

Two recombinant Treponema pallidum proteins Tp0100 and Tp1016 were expressed, purified, and identified by Western Blotting. A total of 600 clinical serum samples were tested with the Tp0100‐based ELISA, the Tp1016‐based ELISA, and the commercial LICA Syphilis TP kit (ChIVD, Beijing, China). The sensitivities were determined by testing 340 samples from individuals with clinically diagnosed primary, secondary, latent, and tertiary syphilis. The specificities were determined by screening 260 samples from healthy controls and individuals with potentially cross‐reactive infections, including leptospirosis, Lyme disease, hepatitis B, tuberculosis, rheumatoid arthritis, systemic lupus erythematosus. Kappa (κ) values were applied to compare the agreement between clinical syphilis diagnosis and the Tp0100‐based ELISA, the Tp1016‐based ELISA, or the LICA Syphilis TP test.

Results

Using clinical syphilis diagnosis as the gold standard, Tp0100 exhibited an overall sensitivity of 95.6% and specificity of 98.1% for testing IgG antibody while Tp1016 demonstrated only an overall sensitivity of 75.0% and specificity of 79.6%. In contrast, the LICA Syphilis TP test revealed an overall sensitivity of 97.6% and specificity of 96.2%. In addition, the overall percent agreement and corresponding κ values were 96.7% (95% CI 95.6%–97.8%) and 0.93 for the Tp0100‐based ELISA, 77.0% (95% CI 74.3%–79.7%) and 0.54 for the Tp1016‐based ELISA, and 97.0% (95% CI 96.0%–98.0%) and 0.94 for the LICA Syphilis TP test, respectively.

Conclusion

The recombinant T. pallidum protein Tp0100 shows promise as a novel diagnostic antigen in the serological tests for syphilis.

The major outer sheath protein forms distinct conformers and multimeric complexes in the outer membrane and periplasm of Treponema denticola

The major outer sheath protein (MOSP) is a prominent constituent of the cell envelope of Treponema denticola (TDE) and one of its principal virulence determinants. Bioinformatics predicts that MOSP consists of N- and C-terminal domains, MOSP^N and MOSP^C. Biophysical analysis of constructs refolded in vitro demonstrated that MOSP^C, previously shown to possess porin activity, forms amphiphilic trimers, while MOSP^N forms an extended hydrophilic monomer. In TDE and E. coli expressing MOSP with a PelB signal sequence (PelB-MOSP), MOSP^C is OM-embedded and surface-exposed, while MOSP^N resides in the periplasm. Immunofluorescence assay, surface proteolysis, and novel cell fractionation schemes revealed that MOSP in TDE exists as outer membrane (OM) and periplasmic trimeric conformers; PelB-MOSP, in contrast, formed only OM-MOSP trimers. Although both conformers form hetero-oligomeric complexes in TDE, only OM-MOSP associates with dentilisin. Mass spectrometry (MS) indicated that OM-MOSP interacts with proteins in addition to dentilisin, most notably, oligopeptide-binding proteins (OBPs) and the β-barrel of BamA. MS also identified candidate partners for periplasmic MOSP, including TDE1658, a spirochete-specific SurA/PrsA ortholog. Collectively, our data suggest that MOSP destined for the TDE OM follows the canonical BAM pathway, while formation of a stable periplasmic conformer involves an export-related, folding pathway not present in E. coli.

Advances and applications of molecular cloning in clinical microbiology

Molecular cloning is based on isolation of a DNA sequence of interest to obtain multiple copies of it in vitro. Application of this technique has become an increasingly important tool in clinical microbiology due to its simplicity, cost effectiveness, rapidity, and reliability. This review entails the recent advances in molecular cloning and its application in the clinical microbiology in the context of polymicrobial infections, recombinant antigens, recombinant vaccines, diagnostic probes, antimicrobial peptides, and recombinant cytokines. Culture-based methods in polymicrobial infection have many limitation, which has been overcome by cloning techniques and provide gold standard technique. Recombinant antigens produced by cloning technique are now being used for screening of HIV, HCV, HBV, CMV, Treponema pallidum, and other clinical infectious agents. Recombinant vaccines for hepatitis B, cholera, influenza A, and other diseases also use recombinant antigens which have replaced the use of live vaccines and thus reduce the risk for adverse effects. Gene probes developed by gene cloning have many applications including in early diagnosis of hereditary diseases, forensic investigations, and routine diagnosis. Industrial application of this technology produces new antibiotics in the form of antimicrobial peptides and recombinant cytokines that can be used as therapeutic agents.

Performance of the 47-kilodalton membrane protein versus DNA polymerase I genes for detection of Treponema pallidum by PCR in ulcers

Treponema pallidum PCR (Tp-PCR) is a direct diagnostic method for primary and secondary syphilis, but there is no recommendation regarding the best choice of target gene. In this study, we sequentially tested 272 specimens from patients with sexually transmitted ulcers using Tp-PCR targeting the tpp47 and then polA genes. The two methods showed similar accuracies and an almost-perfect agreement.

Major proteins and antigens of Treponema denticola

Treponema denticola is a Gram-negative, motile, asaccharolytic, anaerobic spirochaete which along with Porphyromonas gingivalis and Tannerella forsythia has been shown to form a bacterial consortium called the Red Complex that is strongly associated with the clinical progression of chronic periodontitis. T. denticola was grown in continuous culture in a complex medium with a mean generation time of 15.75 h. Samples from two different membrane-enriched preparations and a cytoplasm-enriched preparation were separated by two-dimensional gel electrophoresis and the proteins identified by MALDI-TOF/TOF mass spectrometry. In total, 219 non-redundant proteins were identified including numerous virulence factors, lipoproteins, ABC transporter proteins and enzymes involved in the metabolism of nine different amino acids of which glycine seems to be of particular importance. Novel findings include the identification of several abundant peptide uptake systems, and the identification of three flagellar filament outer layer proteins. Two-dimensional Western blot analysis using sera from mice immunized with formalin-killed T. denticola cells suggested that Msp, PrcA, OppA, OppA10, MglB, TmpC and several flagellar filament proteins are antigenic.

Molecular typing of treponema pallidum clinical strains from Lisbon, Portugal

A molecular system was used to subtype Portuguese Treponema pallidum clinical strains isolated from both skin lesions and blood. The study with this system constitutes the first typing study in a European country. Three T. pallidum subtypes were found: subtypes 14a (50%), 14d (45.2%), and 14f (4.8%). Further studies are needed to better characterize the isolates involved in syphilis outbreaks.

Reactivity of antibodies from syphilis patients to a protein array representing the Treponema pallidum proteome

To identify antigens important in the human immune response to syphilis, the serum antibody reactivity of syphilitic patients was examined with 908 of the 1,039 proteins in the proteome of Treponema pallidum subsp. pallidum using a protein array enzyme-linked immunosorbent assay. Thirty-four proteins exhibited significant reactivity when assayed with human sera from patients in the early latent stage of syphilis. A subset of antigens identified were further scrutinized for antibody reactivity at primary, secondary, and latent disease stages, and the results demonstrate that the humoral immune response to individual T. pallidum proteins develops at different rates during the time course of infection.

Genome scale identification of Treponema pallidum antigens

Antibody responses for 882 of the 1,039 proteins in the proteome of Treponema pallidum were examined. Sera collected from infected rabbits were used to systematically identify 106 antigenic proteins, including 22 previously identified antigens and 84 novel antigens. Additionally, sera collected from rabbits throughout the course of infection demonstrated a progression in the breadth and intensity of humoral immunoreactivity against a representative panel of T. pallidum antigens.

The time-dependent clearance of virulent Treponema pallidum in susceptible and resistant strains of guinea pigs is significantly different

The kinetics of clearance of Treponema pallidum spp. pallidum Nichols from skin and testes of susceptible C4-deficient (C4D) and -resistant Albany (Alb) strains of guinea pigs (gps) was evaluated using the polymerase chain reaction (PCR) and the rabbit infectivity test (RIT). For each strain there were two groups of animals, one infected with virulent T. pallidum (TP) and one control injected with heat-killed treponemes (HKTP). The kinetic studies and their statistical analysis showed that in the C4D strain the microbial clearance in both tissues was significantly slower (p < 0.005) and still incomplete at 3 months after infection. In the Alb strain the clearance was faster and apparently completed within a month. A greater permissiveness in bacterial growth in C4D compared to Alb appears to be one critical factor determining the different rate of local elimination after primary infection. In both strains there was some correlation between the severity and duration of cutaneous lesions and the local persistence of viable organisms. This correlation was not observed in testes. These studies suggest a genetic basis for the strain-specific susceptibility and resistance phenotypes in the pathogenesis of syphilis.

Identification of homologs for thioredoxin, peptidyl prolyl cis-trans isomerase, and glycerophosphodiester phosphodiesterase in outer membrane fractions from Treponema pallidum, the syphilis spirochete

In this study, we characterized candidate rare outer membrane (OM) proteins with apparent molecular masses of 19, 27, 38, and 38.5 kDa, which had been identified previously in OM fractions from Treponema pallidum (J. D. Radolf et al., Infect. Immun. 63:4244-4252, 1995). Using N-terminal and internal amino acid sequences, a probe for the 19-kDa candidate was PCR amplified and used to screen a T. pallidum genomic library in Lambda Zap II. The corresponding gene (tlp) encoded a homolog for periplasmic thioredoxin-like proteins (Tlp), which reduce c-type cytochromes. A degenerate oligonucleotide derived from the N terminus of the 27-kDa protein was used to PCR amplify a duplex probe from a T. pallidum genomic library in pBluescript II SK+. With this probe, the corresponding gene (ppiB) was identified and found to code for a presumptive periplasmic cyclophilin B-type peptidyl prolyl cis-trans isomerase (PpiB). We postulate that PpiB assists the folding of proteins within the T. pallidum periplasmic space. The N terminus of the 38-kDa candidate was blocked to Edman degradation. However, internal sequence data revealed that it was basic membrane protein (Bmp), a previously characterized, signal peptidase I-processed protein. Triton X-114 phase partitioning revealed that despite its name, Bmp is hydrophilic and therefore likely to be periplasmic. The final candidate was also blocked to Edman degradation; as before, a duplex probe was PCR amplified with degenerate primers derived from internal sequences. The corresponding gene (glpQ) coded for a presumptively lipid-modified homolog of glycerophosphodiester phosphodiesterase (GlpQ). Based upon findings with other treponemal lipoproteins, the hydrophilic GlpQ polypeptide is thought to be anchored by N-terminal lipids to the periplasmic leaflet(s) of the cytoplasmic membrane and/or OM. The discovery of T. pallidum periplasmic proteins with potentially defined functions provides fresh insights into a poorly understood aspect of treponemal physiology. At the same time, however, these findings also raise important issues regarding the use of OM preparations for identifying rare OM proteins of T. pallidum.

Tromp1, a putative rare outer membrane protein, is anchored by an uncleaved signal sequence to the Treponema pallidum cytoplasmic membrane

Treponema pallidum rare outer membrane protein 1 (Tromp1) has extensive sequence homology with substrate-binding proteins of ATP-binding cassette transporters. Because such proteins typically are periplasmic or cytoplasmic membrane associated, experiments were conducted to clarify Tromp1's physicochemical properties and cellular location in T. pallidum. Comparison of the sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobilities of (i) native Tromp1 and Tromp1 synthesized by coupled in vitro transcription-translation and (ii) native Tromp1 and recombinant Tromp1 lacking the N-terminal signal sequence revealed that the native protein is not processed. Other studies demonstrated that recombinant Tromp1 lacks three basic porin-like properties: (i) the ability to form aqueous channels in liposomes which permit the influx of small hydrophilic solutes, (ii) an extensive beta-sheet secondary structure, and (iii) amphiphilicity. Subsurface localization of native Tromp1 was demonstrated by immunofluorescence analysis of treponemes encapsulated in gel microdroplets, while opsonization assays failed to detect surface-exposed Tromp1. Incubation of motile treponemes with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)-diazarine, a photoactivatable, lipophilic probe, also did not result in the detection of Tromp1 within the outer membranes of intact treponemes but, instead, resulted in the labeling of a basic 30.5-kDa presumptive outer membrane protein. Finally, analysis of fractionated treponemes revealed that native Tromp1 is associated predominantly with cell cylinders. These findings comprise a body of evidence that Tromp1 actually is anchored by an uncleaved signal sequence to the periplasmic face of the T. pallidum cytoplasmic membrane, where it likely subserves a transport-related function.

Target organs of infection in guinea pigs with acquired congenital syphilis

The target organs of infection in guinea pigs with asymptomatic acquired or congenital syphilis were identified by PCR and in some cases by rabbit infectivity test (RIT). The prevalence of Treponema pallidum DNA was examined in the following seven organs: the inguinal and mesenteric lymph nodes, spleen, liver, kidney, heart, and brain. Test samples consisted of 95 organs from two genetically different strains of female guinea pigs (C4-deficient and Albany) with different susceptibilities to cutaneous infection by T. pallidum and 195 organs from their asymptomatic offspring. Twenty organs from dams of both strains injected with heat-killed T. pallidum and 19 organs from their progeny served as negative controls. The infections of mothers and neonates were documented by PCR, RIT, and serology. Though any of the organs tested could be infected, there was a spirochetal predilection for some anatomical locations, such as the lymph nodes, heart, and brain, regardless of the strain, route of maternal infection, and age. None of the 49 organs collected from control animals were positive by PCR. In infected C4-deficient dams, one to four organs were positive by PCR, whereas the organs of 7 of their 27 (25%) asymptomatic offspring were treponemal DNA negative, despite evidence of immunoglobulin M treponemal antibodies. Comparative analysis done by both PCR and RIT on a limited number of samples showed 90% agreement between results. An examination of multiple samples obtained from single organs demonstrated that even within 24 h of spirochetemia, when most organs appeared to be infected, not all samples from an individual organ were positive by PCR. A specific immunological response in guinea pigs with congenital syphilis was a more consistent parameter of vertical transmission than was an analysis of T. pallidum DNA.

Diagnosis of congenital syphilis from placental examination: comparison of histopathology, Steiner stain, and polymerase chain reaction for Treponema pallidum DNA

Congenital syphilis is often a presumptive diagnosis (based on serologies), because confirmation requires identification of Treponema pallidum in fetal/neonatal tissues or in the placenta. Placental histological features associated with congenital syphilis include the triad of enlarged hypercellular villi, proliferative fetal vascular changes, and acute or chronic villitis. The authors blindly evaluated 49 formalin-fixed, paraffin-embedded placentas (38 with positive maternal syphilis serologies; 11 with negative serologies) and compared results of histology, Steiner stain, and polymerase chain reaction (PCR) for T pallidum DNA. Histology was categorized as positive (triad present), suspicious (two thirds of triad present), or negative. Treponemal DNA was detected by amplifying a 189 base pair region of the 47 kd treponemal membrane antigen with 44 cycles of PCR; products were detected by Southern blot. Placentas from the 11 seronegative mothers were all negative by histology, Steiner stain, and PCR. Among the 38 placentas from serologically positive mothers, 4 had positive histology (2 of 4 positive Steiner, 4 of 4 positive PCR); 6 had suggestive histology (0 of 6 positive Steiner; 1 of 6 positive PCR); and, 28 had negative histology (0 of 28 positive Steiner; 1 of 28 positive PCR). PCR identification of treponemal DNA was significantly associated with the triad (P = .0003), proliferative fetal vascular changes (P = .0003), acute villitis (P = .003), chronic villitis (P = .004), and spirochetes on Steiner stain (P = .01). These results (1) confirm a strong association between placental histopathologic features and congenital syphilis; (2) indicate that when such features are present, PCR of placental tissue may confirm the diagnosis of congenital syphilis; and (3) suggest that even when such features are absent, PCR of placental tissue may identify additional cases of histologically unsuspected congenital syphilis.

Simultaneous PCR detection of Haemophilus ducreyi, Treponema pallidum, and herpes simplex virus types 1 and 2 from genital ulcers

A multiplex PCR (M-PCR) assay with colorimetric detection was devised for the simultaneous amplification of DNA targets from Haemophilus ducreyi, Treponema pallidum, and herpes simplex virus (HSV) types 1 and 2. By using target-specific oligonucleotides in a microwell format, 298 genital ulcer swab specimens collected in New Orleans during three intervals from 1992 through 1994 were evaluated. The results of the M-PCR assay were compared with the results of dark-field microscopy and H. ducreyi culture on two different culture media. HSV culture results were available for 99 specimens collected during the third interval. Confirmatory PCR assays targeting different gene sequences for each of the three organisms were used to validate the M-PCR results. Specimens were resolved as positive for the determination of sensitivity if the reference diagnostic test was positive or if the results of both the M-PCR and the confirmatory PCR were positive. The resolved sensitivities of M-PCR for HSV, H. ducreyi, and T. pallidum were 100, 98.4, and 91%, respectively. The resolved sensitivities of HSV culture, H. ducreyi culture, and dark-field microscopy were 71.8, 74.2, and 81%, respectively. These results indicate that the M-PCR assay is more sensitive than standard diagnostic tests for the detection of HSV, H. ducreyi, and T. pallidum from genital ulcers.

Expression and sequence analysis of a Treponema pallidum gene, tpn38(b), encoding an exported protein with homology to T. pallidum and Borrelia burgdorferi proteins

An Escherichia coli clone containing recombinant plasmid C19 was identified from a Treponema pallidum genomic DNA library by in situ immunoassay. E. coli maxicells containing pC19 synthesized a treponemal protein doublet of 39.2 and 38.2 kDa, designated TpN38(b). Pulse-chase and protein processing studies showed that TpN38(b) is synthesized with a cleavable amino-terminal signal peptide. A 2.0-kb fragment of pC19 containing the tpn38(b) gene was subcloned and sequenced. The tpn38(b) gene is 1029 nucleotides long and encodes a protein of 343 amino acids with a calculated molecular mass of 37.9 kDa. The deduced amino acid sequence of TpN38(b) has homology with the T. pallidum TpN35 lipoprotein and the Borrelia burgdorferi BmpA, BmpB, BmpC, and BmpD proteins.

Similarity between the 38-kilodalton lipoprotein of Treponema pallidum and the glucose/galactose-binding (MglB) protein of Escherichia coli

The recent discovery that abundant and immunogenic lipoproteins constitute the integral membrane proteins of Treponema pallidum has prompted efforts to investigate their importance in the physiology and ultrastructure of the organism and in immune responses during infection. Earlier studies identified a 38-kDa lipoprotein of T. pallidum believed to be specific to the pathogen. In the present study, monoclonal antibodies generated against the 38-kDa lipoprotein of T. pallidum reacted with cognate 37-kDa molecules in the nonpathogens Treponema phagedenis, Treponema denticola, and Treponema refringens. Cloning and expression of the 38-kDa-lipoprotein gene of T. pallidum in Escherichia coli revealed that the recombinant product displayed a slightly larger (39-kDa) apparent molecular mass but remained reactive with anti-38-kDa-protein monoclonal antibodies. The recombinant product was processed and acylated in E. coli. DNA and amino acid sequence analyses indicated an open reading frame encoding 403 amino acids, with the first 25 amino acids corresponding to a leader peptide terminated by a signal peptidase II processing site of Val-Val-Gly-Cys. The predicted mature protein is 378 amino acids in length with a deduced molecular weight of 40,422 (excluding acylation). Southern blotting failed to demonstrate in nonpathogenic treponemes genomic sequences homologous with the 38-kDa-lipoprotein gene of T. pallidum. Computer analysis revealed that the 38-kDa lipoprotein of T. pallidum had 34.2% identity and 58.9% similarity with the glucose/galactose-binding protein (MglB) of E. coli and Salmonella typhimurium. Furthermore, of the 19 amino acids of MglB involved in carbohydrate binding, the 38-kDa lipoprotein had identity with 11. These studies have allowed the first putative functional assignment (carbohydrate binding) to a T. pallidum integral membrane protein. Recognition of this potential physiological role for the 38-kDa lipoprotein underscores the possibility that the membrane biology of T. pallidum may more closely resemble that of gram-positive organisms, which also utilize lipoproteins as anchored transporters, than that of gram-negative bacteria to which T. pallidum often is analogized.

Identification and characterization of the Treponema pallidum tpn50 gene, an ompA homolog

Treponema pallidum is a pathogenic spirochete that has no known genetic exchange mechanisms. In order to identify treponemal genes encoding surface and secreted proteins, we carried out TnphoA mutagenesis of a T. pallidum genomic DNA library in Escherichia coli. Several of the resulting clones expressed enzymatically active T. pallidum-alkaline phosphatase fusion proteins. The DNA sequence of the 5' portion of a number of the treponemal genes was obtained and analyzed. A recombinant clone harboring plasmid p4A2 that encoded a treponemal protein with an approximate molecular mass of 50,000 Da was identified. Plasmid p4A2 contained an open reading frame of 1,251 nucleotides that resulted in a predicted protein of 417 amino acids with a calculated molecular mass of 47,582 Da. We have named this gene tpn50 in accordance with the current nomenclature for T. pallidum genes. A 1.9-kb HincII-ClaI fragment from p4A2 that contained the tpn50 gene was subcloned to produce p4A2HC2. Comparison of the predicted amino acid sequence of TpN50 with protein sequences in the National Center for Biotechnology Information data base indicated statistically significant homology to the Pseudomonas sp. OprF, E. coli OmpA, Bordetella avium OmpA, Neisseria meningitidis RmpM, Neisseria gonorrhoeae PIII, Haemophilus influenzae P6, E. coli PAL, and Legionella pneumophila PAL proteins. These proteins are all members of a family of outer membrane proteins that are present in gram-negative bacteria. The tpn50 gene complemented E. coli ompA mutations on the basis of two separate criteria. First, morphometry and electron microscopy data showed that E. coli C386 (ompA lpp) cells harboring plasmid vector pEBH21 were rounded while cells of the same strain harboring p4A2HC2 (TpN50+), pWW2200 (OprF+), or pRD87 (OmpA+) were rod shaped. Second, E. coli BRE51 (MC4100 delta sulA-ompA) cells harboring pEBH21 grew poorly at 42 degrees C in minimal medium, while the growth of BRE51 cells harboring p4A2HC2 was similar to that of the parental MC4100 cells. These results demonstrate that the TpN50 protein is functionally equivalent to the E. coli OmpA protein. If TpN50 functions in a similar fashion in T. pallidum, then it may be localized to the treponemal outer membrane.

Polypeptides of Treponema pallidum: progress toward understanding their structural, functional, and immunologic roles. Treponema Pallidum Polypeptide Research Group

Treponema pallidum subsp. pallidum, the spirochete that causes syphilis, is unusual in a number of respects, including its small genome size, inability to grow under standard in vitro culture conditions, microaerophilism, apparent paucity of outer membrane proteins, structurally complex periplasmic flagella, and ability to evade the host immune responses and cause disease over a period of years to decades. Many of these attributes are related ultimately to its protein content. Our knowledge of the activities, structure, and immunogenicity of its proteins has been expanded by the application of recombinant DNA, hybridoma, and structural fractionation techniques. The purpose of this monograph is to summarize and correlate this new information by using two-dimensional gel electrophoresis, monoclonal antibody reactivity, sequence data, and other properties as the bases of polypeptide identification. The protein profiles of the T. pallidum subspecies causing syphilis, yaws, and endemic syphilis are virtually indistinguishable but differ considerably from those of other treponemal species. Among the most abundant polypeptides are a group of lipoproteins of unknown function that appear to be important in the immune response during syphilitic infection. The periplasmic flagella of T. pallidum and other spirochetes are unique with regard to their protein content and ultrastructure, as well as their periplasmic location. They are composed of three core proteins (homologous to the other members of the eubacterial flagellin family) and a single, unrelated sheath protein; the functional significance of this arrangement is not understood at present. Although the bacterium contains the chaperonins GroEL and DnaK, these proteins are not under the control of the heat shock regulon as they are in most organisms. Studies of the immunogenicity of T. pallidum proteins indicate that many may be useful for immunodiagnosis and immunoprotection. Future goals in T. pallidum polypeptide research include continued elucidation of their structural locations and functional activities, identification and characterization of the low-abundance outer membrane proteins, further study of the immunoprotective and immunodiagnostic potential of T. pallidum proteins, and clarification of the roles of treponemal proteins in pathogenesis.

Detection of Treponema pallidum in early syphilis by DNA amplification

By using experimentally infected rabbits as a model for early syphilis, the applicability of in vitro DNA amplification was explored for detection of Treponema pallidum. It was determined that whole blood in heparin or EDTA (but not serum), lesion exudate, and punch biopsy as well as swabs of lesions are useful specimens for examination by the polymerase chain reaction. Swabs do not require special diluents, and the specimens, whether kept at room temperature or frozen, are well suited for use in the polymerase chain reaction.

Detection by polymerase chain reaction of Treponema pallidum DNA in cerebrospinal fluid from neurosyphilis patients before and after antibiotic treatment

A polymerase chain reaction with nested primer pairs based on the DNA sequence of the 39-kDa bmp gene of Treponema pallidum subsp. pallidum is described. The method allowed the detection of purified T. pallidum DNA equivalent to the amount of DNA in a single bacterium and was specific for T. pallidum subspecies. After concentration of DNA, using diatomaceous earth, it was possible to detect about 100 treponemes in 1 ml of cerebrospinal fluid. Cerebrospinal fluid samples from a total of 29 symptomatic and asymptomatic patients with neurosyphilis were tested for the presence of treponemal DNA before and at various intervals after intravenous treatment with penicillin. Prior to the penicillin treatment, we detected T. pallidum DNA in 5 of 7 patients with acute symptomatic neurosyphilis, in none of the 4 patients with chronic symptomatic neurosyphilis tested before treatment, and in 2 of 16 patients with asymptomatic neurosyphilis. Unexpectedly, T. pallidum DNA was also often detected in cerebrospinal fluid long after intervenous treatment with penicillin, sometimes up to 3 years after therapy.

Molecular cloning and characterization of a 35.5-kilodalton lipoprotein of Treponema pallidum

A clone expressing a 35.5-kDa recombinant treponemal protein was isolated from a genomic DNA library constructed from Treponema pallidum street strain 14. Polyclonal antiserum raised against the recombinant protein reacted with a corresponding native protein of comparable size in T. pallidum that is specific to the pathogenic treponemes. Radiolabeling of the recombinant protein with [3H]palmitate demonstrated that it is lipid modified. Like other recently characterized T. pallidum lipoproteins, the 35.5-kDa lipoprotein partitioned into the detergent phase from T. pallidum cells fractionated with Triton X-114, suggesting that it is an integral membrane protein. Processing of the recombinant 35.5-kDa lipoprotein from a precursor form to a smaller mature form was not evident in pulse-chase experiments. However, pretreatment of Escherichia coli cells expressing the 35.5-kDa lipoprotein with inhibitors of protein processing or translocation revealed the existence of a higher-molecular-mass precursor. Gene fusion studies with the transposon TnphoA demonstrated the presence of an export signal in the 35.5-kDa lipoprotein that promotes the extracytoplasmic localization of a 35.5-kDa lipoprotein-PhoA hybrid.

Expression in Escherichia coli of the 37-kilodalton endoflagellar sheath protein of Treponema pallidum by use of the polymerase chain reaction and a T7 expression system

We previously reported the complete primary structure of the 37-kilodalton endoflagellar sheath protein (FlaA) of Treponema pallidum. However, we were unable to determine the nucleotide sequence of flaA upstream of amino acid 10. The desired nucleotide sequence was obtained by use of a strategy based upon the polymerase chain reaction and was found to contain a consensus Escherichia coli promoter, a ribosomal binding site, and a 20-amino-acid signal peptide. Expression of FlaA in E. coli was achieved by cloning polymerase chain reaction-derived constructs lacking the native T. pallidum promoter into a temperature-inducible T7 expression system. Pulse-chase and ethanol inhibition analyses of protein processing in E. coli cells and minicells, respectively, indicated that processing of the FlaA precursor was incomplete. Native and recombinant FlaA were identical as assessed by antibody reactivity and sodium dodecyl sulfate- and two-dimensional polyacrylamide gel electrophoretic mobilities. Soluble FlaA was not detected in either the cytoplasmic or the periplasmic fractions of E. coli transformants. Fractionation of E. coli cell envelopes unexpectedly revealed that FlaA precursor and FlaA were associated with both the cytoplasmic and outer membranes. This is the first report of expression in E. coli of a T. pallidum protein which could not be cloned or expressed with its native promoter. Our data also indicate that information obtained in E. coli regarding the subcellular location of cloned treponemal proteins must be cautiously extrapolated to T. pallidum.

Molecular and antigenic analysis of treponemes

The treponemes comprise the essentially non-cultivable Treponema pallidum subspecies (agents of syphilis, yaws and other human trepanematoses), the gut pathogen of pigs, T. hydysenteriae, and a group of antigenically related, cultivable species, some of which are strongly implicated in human periodontal or gastrointestinal disease. Technical developments during the last decade have made possible the molecular analysis of components of this diverse group of organisms. Polypeptides and other macromolecular components have been characterized by techniques including electron microscopy, gel electrophoresis and immunoblotting. Antigenic analysis has been greatly enhanced by the use of monoclonal antibodies. Finally, DNA cloning and genetic manipulation have enabled the detailed investigation of important antigens at a genetic, structural and functional level. We examine these developments and provide a current overview of the data now available, which is an important foundation for applications in diagnosis, therapy, and, potentially, immunization against disease.

Molecular cloning and characterization of the 15-kilodalton major immunogen of Treponema pallidum

Pathogen-specific membrane immunogens of Treponema pallidum subsp. pallidum (T. pallidum) have been identified previously by phase partitioning with the nonionic detergent Triton X-114. One of these antigens, a 15-kilodalton (kDa) polypeptide, is expressed in relatively small quantities in T. pallidum but is highly immunogenic in both human and experimental syphilis. The native T. pallidum antigen was purified to homogeneity from the mixture of Triton X-114 detergent-phase proteins by chromatofocusing. Recombinant Escherichia coli clones were selected from a T. pallidum genomic DNA library by using monoclonal antibodies specific to the 15-kDa antigen; immunoblotting and minicell analyses confirmed expression of the 15-kDa protein in the transformants. Southern hybridization with a 1.1-kilobase fragment of DNA encoding the 15-kDa-antigen gene indicated that the gene is probably present in a single copy within the genomes of both T. pallidum and T. pallidum subsp. pertenue (the agent of yaws), while it is absent from the genome of the nonpathogenic Treponema phagedenis biotype Reiter. Cell fractionation studies with Triton X-114 demonstrated that the recombinant polypeptide possesses hydrophobic properties similar to those of the native antigen and localized the cloned 15-kDa antigen to the inner membrane of E. coli. Protein processing experiments in minicells revealed that a precursor appears to be processed to the mature 15-kDa polypeptide.

Molecular characterization of the pathogen-specific, 34-kilodalton membrane immunogen of Treponema pallidum

The 34-kilodalton (kDa) antigen of Treponema pallidum subsp. pallidum (T. pallidum) is a pathogen-specific integral membrane protein. DNA sequence analysis of the cloned gene revealed an open reading frame encoding a primary product of 204 residues with a molecular mass of 22,087 daltons. Sequences that correspond to a consensus Escherichia coli promoter and a ribosome-binding site were found upstream from the AUG start codon that begins the open reading frame, suggesting that the cloned gene can use its own regulatory sequences for expression. Examination of the deduced amino acid sequence revealed the presence of a typical procaryotic leader peptide 19 amino acids long; processing results in a mature molecule with a molecular mass of 20,123 daltons. Pulse-chase experiments with E. coli minicells confirmed that the 34-kDa antigen is synthesized as a higher-molecular-weight precursor that is processed to a mature form with the electrophoretic mobility that is characteristic for this protein. The presence in the leader peptide of the sequence Phe-Ser-Ala-Cys suggested that the 34-kDa antigen is a proteolipid. Although hydropathy analysis of the deduced amino acid sequence of the mature 34-kDa antigen predicted that the molecule was primarily hydrophilic, both the native and recombinant 34-kDa molecules displayed hydrophobic biochemical behavior by fractionating into the detergent phase after extraction of intact organisms with Triton X-114. Cell fractionation experiments with E. coli showed that the 34-kDa molecule was localized in both the inner and outer membranes of the recombinant host. The combined data demonstrate that the 34-kDa antigen is an integral membrane protein that behaves in a biochemically consistent manner in both T. pallidum and E. coli.

Molecular cloning and DNA sequence analysis of the 37-kilodalton endoflagellar sheath protein gene of Treponema pallidum

We have used a combination of nucleotide and N-terminal-amino-acid-sequence analyses to determine the primary structure of the 37-kilodalton (kDa) endoflagellar outer layer, or sheath, protein. Initially, a lambda gt11 clone (designated lambda A34) expressing a portion of the 37-kDa protein was selected from a Treponema pallidum genomic library with a murine monoclonal antibody (H9-2) directed against an epitope of the 37-kDa protein. The insert from lambda A34 provided a probe with which a chimeric plasmid (pR14) encoding all but the nine N-terminal amino acids of the entire protein was selected from a T. pallidum(pBR322) genomic library. The nine N-terminal amino acids determined by amino acid sequencing were combined with the DNA sequence encoded by pR14 to determine the primary structure of the entire 37-kDa protein; the combined sequence made up a polypeptide with a calculated molecular mass of 36,948 Da. Approximately one-third of the deduced sequence was confirmed by N-terminal amino acid analysis of tryptic peptides from the purified 37-kDa protein. Repeated attempts to clone upstream portions of the gene (flaA) by using a variety of strategies were unsuccessful, suggesting that unregulated expression of the intact sheath protein or of its most amino-terminal portions is toxic in Escherichia coli. These studies should provide the basis for further molecular investigations of the endoflagellar apparatus and of treponemal motility.

Acylation of the 47-kilodalton major membrane immunogen of Treponema pallidum determines its hydrophobicity

The 47-kilodalton (kDa) major integral membrane immunogen of Treponema pallidum was recently found to be a proteolipid. Similar two-dimensional electrophoretic mobilities and common hydrophobic properties displayed by the native (T. pallidum) and recombinant (Escherichia coli) 47-kDa antigens suggested that the recombinant antigen also possesses covalently bound lipid. Both intact E. coli and E. coli minicells acylated the 47-kDa antigen; immunoprecipitation with a monoclonal antibody specific for the 47-kDa immunogen supported the contention that the acylated product of E. coli corresponds to the cloned T. pallidum antigen. Triton X-114 phase partitioning was used to compare the relative hydrophobicities of 47-kDa molecules synthesized by in vitro and in vivo protein translation systems. The products synthesized by T. pallidum, intact E. coli, or E. coli minicells were hydrophobic, while the protein synthesized in an E. coli cell-free translation system was hydrophilic. Processing experiments with E. coli suggested that the primary gene translation product of the protein is not synthesized in a precursor form, unlike other bacterial proteolipids. These results indicate that the hydrophobicity of the 47-kDa integral membrane protein is conferred substantially by the covalently attached lipid(s). The biochemical similarities between the native and recombinant 47-kDa proteolipids will provide a foundation for future investigations into the structure and immunogenicity of this integral membrane protein of T. pallidum.

Evaluation of Western immunoblotting technique in the serological diagnosis of human syphilitic infections

Purified human syphilitic antibodies against both 15.5 Kd and 45 Kd treponemal antigens appear T. pallidum specific and do not cross react with antigens possessed by other treponemes (T. phagedenis, T. hyodysenteriae and a human intestinal treponeme). By using Western immunoblotting technique, 107 out of 110 syphilitic patients and 291 out of 294 subjects with serologically positive diagnostic tests for syphilis were found to have in their sera antibodies against a 15.5 Kd specific antigen of T. pallidum. These antibodies were present in 100% of the patient with secondary or early latent syphilis, both untreated and treated, in 98.24% of those with late latent treated syphilis and in 100% of patients with neurosyphilis. On the contrary, they were absent in 47 patients with false positive reactions for syphilis and in 121 healthy blood donors. For these reasons, the demonstration of these kind of antibodies in a patient's serum can be considered of high value in differentiating syphilitic patients from non infected individuals.

Sequence analysis of the 47-kilodalton major integral membrane immunogen of Treponema pallidum

The complete primary amino acid sequence for the 47-kilodalton (kDa) major integral membrane immunogen of Treponema pallidum subsp. pallidum was obtained by using a combined strategy of DNA sequencing (of the cloned gene in Escherichia coli) and N-terminal amino acid sequencing of the native (T. pallidum subsp. pallidum-derived) antigen. An open reading frame believed to encode the 47-kDa antigen comprised 367 amino acid codons, which gave rise to a calculated molecular weight for the corresponding antigen of 40,701. Of the 367 amino acids, 113 (31%) were sequenced by N-terminal amino acid sequencing of trypsin and hydroxylamine cleavage fragments of the native molecule isolated from T. pallidum subsp. pallidum; amino acid sequence data had a 100% correlation with that of the amino acid sequence predicted from DNA sequencing of the cloned gene in E. coli. Although no consensus sequences for the initiation of transcription or translation were readily identifiable immediately 5' to the putative methionine start codon, a 63-base-pair PstI fragment located 159 nucleotides upstream was required for expression of the 47-kDa antigen in E. coli. The 47-kDa antigen sequence did not reveal a typical leader sequence. The overall G+C content for the DNA corresponding to the structural gene was 53%. Hydrophilicity analysis identified at least one major hydrophilic domain of the protein near the N terminus of the molecule which potentially represents an immunodominant epitope. No repetitive primary sequence epitopes were found. The combined data provide the molecular basis for further structural and functional studies regarding the role of the antigen in the immunopathogenesis of treponemal disease.