Production of recombinant Bartonella henselae 17-kDa protein for antibody-capture enzyme-linked immunosorbent assay

Development and Diagnostic Potential of a Novel Bartonella henselae-Specific Immunoglobulin

Bartonella henselae is a gram-negative rod-shaped bacterium and is the primary causative agent of Cat Scratch Disease (CSD). Although the prevalence of CSD is low in the human population, the possibility of developing multi-organ complications, especially in vulnerable individuals, remains a serious cause for concern. The immunofluorescent assay (IFA) is currently one of the most common laboratory tests for the detection of antibodies to B. henselae in serum, however, it has several disadvantages. The enzyme-linked immunosorbent assay (ELISA) technique offers a more quantitative, sensitive, and cost-effective alternative to conventional IFAs. Here, we report the purification of a novel bioidentical polyclonal antibody from discarded human serum for use as a standard in ELISAs against B. henselae. This novel method of antibody production overcomes the many limitations of animal-derived antibodies while also offering a more robust, reproducible, and scalable antibody production alternative for the diagnosis of CSD.

HIV and skin infections

HIV infection alters the skin microbiome and predisposes to a wide range of cutaneous infections, from atypical presentations of common skin infections to severe disseminated infections involving the skin that are AIDS-defining illnesses. Bacterial infection of the skin, most commonly caused by Staphylococcus aureus, occurs frequently and can result in bacteremia. Nontuberculous mycobacterial infections that are usually localized to the skin may disseminate, and guidance on the treatment of these infections is limited. Herpes simplex can be severe, and less common presentations such as herpetic sycosis and herpes vegetans have been reported. Severe herpes zoster, including disseminated infection, requires intravenous antiviral treatment. Viral warts can be particularly difficult to treat, and in atypical or treatment-resistant cases a biopsy should be considered. Superficial candidosis occurs very commonly in people living with HIV, and antifungal resistance is an increasing problem in non-albicans Candida species. Systemic infections carry a poor prognosis. In tropical settings the endemic mycoses including histoplasmosis are a problem for people living with HIV, and opportunistic infections can affect those with advanced HIV in all parts of the world. Most cutaneous infections can develop or worsen as a result of immune reconstitution in the weeks to months after starting antiretroviral therapy. Direct microscopic examination of clinical material can facilitate rapid diagnosis and treatment initiation, although culture is important to provide microbiological confirmation and guide treatment.

Limitations of Serological Diagnosis of Typical Cat Scratch Disease and Recommendations for the Diagnostic Procedure

Introduction

Cat scratch disease (CSD) is the most common cause of bacterial infectious lymphadenopathy, especially in children, but its diagnosis still remains challenging. Serological assays are widely applied due to their simplicity and the non-invasive sampling. However, these techniques present several limitations, including not well-defined antigen preparation, assay conditions and cutoff titers, severe cross-reactions with other species and organisms, and the notably ranging seroprevalence in the normal population. The objective of this study is to review the literature in order to determine the best diagnostic procedure for the diagnosis of CSD.

Methods

Databases including PubMed, Medline, Google Scholar, and Google were searched to determine the best diagnostic procedure for the diagnosis of CSD. A total of 437 papers were identified and screened, and after exclusion of papers that did not fulfill the including criteria, 63 papers were used.

Results

It was revealed that sensitivities of serological assays varied from 10% to 100%. Indeed, more than half of the studies reported a sensitivity lower than 70%, while 71% of them had a sensitivity lower than 80%. Moreover, specificities of serological assays ranged from 15% to 100%, with 25 assays reporting a specificity lower than 90%.

Conclusion

It is considered that molecular assays should be the gold standard technique for CSD confirmation, and physicians are reinforced to proceed to lymph node biopsy in suspicious CSD cases.

In silico analyses and design of chimeric proteins containing epitopes of Bartonella henselae antigens for the control of cat scratch disease

Bartonella henselae is a Gram-negative bacterium that causes cat scratch disease (CSD), as well as bacteremia, endocarditis, and other clinical presentations. CSD remains one of the most common infections caused by bacteria in the genus Bartonella, and it is transmitted to humans through a scratch or cat bite. Vaccination and more efficient diagnostic methods would represent a promising and sustainable alternative measure for CSD control in humans and animals. Here, we described the in silico analyses and design of three recombinant chimeric proteins (rC1, rC2, and rC3), for use in the control of CSD. The chimeras were constructed with epitopes identified from the sequences of the GroEL, 17 kDa, P26, BadA, Pap31, OMP 89, and OMP 43, previously described as the most important B. henselae antigens. The rC1, rC2, and rC3 were expressed and purified using a heterologous system based on Escherichia coli and reacted with antibodies present in the sera of humans naturally infected. The chimeric proteins were used to immunize mice using Freund adjuvant, and the humoral immune response was evaluated. Animals immunized with rC1 and rC3 showed a significant IgG antibodies response from the 28th day (P < 0.05), and the animals immunized with the rC2 from the 35th day (P < 0.05) remained until the 56th day of experimentation, with a titer of 1:3200 (P < 0.05), 1:1600 (P < 0.05) and 1:1600 (P < 0.05) from rC1, rC2, and rC3, respectively. Significant production of IgA and IgG1 isotype was detected in animals immunized with rC1 and rC2 proteins. Additionally, analysis using 13 serum samples from naturally infected patients showed that the proteins are recognized by antibodies present in sera, reinforcing the possibility of using these chimeras for CSD control. KEY POINTS: • The recombinant chimeras were expressed in Escherichia coli with 37 kDa (rC1), 35 kDa (rC2), and 38 kDa (rC3). • Animals immunized with rC1, rC2, and rC3 showed significant antibody response. • The chimeras were recognized by the sera of naturally infected patients.

Analytical and clinical evaluation of new automated chemiluminescent immunoassays for the detection of IgG and IgM anti-Bartonella henselae antibodies

Serological diagnosis of Bartonella henselae infection mainly rely on microscopic immunofluorescence assays (IFA), which are however time-consuming and poorly standardized. The aim of the study was to assess the use of the new fully automated VirClia® chemiluminescent immunoassays for the detection of IgG and IgM anti-B. henselae antibodies. Eighty-one patients with a well-defined B. henselae infection as well as 80 patients with an alternative disease were included. The VirClia® IgG antibody assay showed a sensitivity of 79.0% and a specificity of 93.8% for the diagnosis of B. henselae infection. For the VirClia® IgM assay, results were more conflicting with a sensitivity of 42.0% and a specificity of 98.2% to predict IFA IgM results. In 11 additional patients with uninterpretable IFA due to autoimmune antibodies, VirClia® assays were able to deliver valuable quantitative results. The VirClia® IgG assay shows good analytical and clinical performances and could be easily integrated in the diagnostic workflow of B. henselae infection.

Development of a Specific and Sensitive Enzyme-Linked Immunosorbent Assay as an In Vitro Diagnostic Tool for Detection of Bartonella henselae Antibodies in Human Serum

Bartonella henselae causes cat scratch disease and several other clinical entities. Infections with B. henselae are frequently occurring; however, the infection is only rarely diagnosed, mainly due to a lack of knowledge in the medical community. Microscopic immunofluorescence assays (IFA) are widely used for the serodiagnosis of B. henselae infections but are laborious and time-consuming, and interpretation is subjective. An easy and reliable method for the serological diagnosis of B. henselae infections is needed to overcome the shortcomings of the current IFA. Here, we report the development of an ELISA detecting human anti-B. henselae antibodies from serum samples. By separating the water-insoluble fraction of B. henselae Houston-1 via ion-exchange chromatography, 16 subfractions were generated and tested for immunoreactivity via line blotting. One particular fraction (fraction 24) was selected and spotted on ELISA plates using an industrial production platform. By use of well-characterized human sera from the strictly quality-controlled serum library of the German National Consiliary Laboratory for Bartonella infections, the sensitivity of this ELISA was 100% for PCR-proven infections and 76% for clinically suspected infections at a specificity of 93%. This ELISA is therefore a reliable high-throughput method allowing the serodiagnosis of B. henselae infections.

Bartonella Species, an Emerging Cause of Blood-Culture-Negative Endocarditis

Since the reclassification of the genus Bartonella in 1993, the number of species has grown from 1 to 45 currently designated members. Likewise, the association of different Bartonella species with human disease continues to grow, as does the range of clinical presentations associated with these bacteria. Among these, blood-culture-negative endocarditis stands out as a common, often undiagnosed, clinical presentation of infection with several different Bartonella species. The limitations of laboratory tests resulting in this underdiagnosis of Bartonella endocarditis are discussed. The varied clinical picture of Bartonella infection and a review of clinical aspects of endocarditis caused by Bartonella are presented. We also summarize the current knowledge of the molecular basis of Bartonella pathogenesis, focusing on surface adhesins in the two Bartonella species that most commonly cause endocarditis, B. henselae and B. quintana. We discuss evidence that surface adhesins are important factors for autoaggregation and biofilm formation by Bartonella species. Finally, we propose that biofilm formation is a critical step in the formation of vegetative masses during Bartonella-mediated endocarditis and represents a potential reservoir for persistence by these bacteria.

Development of an enzyme-linked immunosorbent assay for Bartonella henselae infection detection

Several serological diagnostics rely on enzyme-linked immunosorbent assay (ELISA) to detect bacterial infections. However, for some pathogens, including Bartonella henselae, diagnosis still depends on manually intensive, time-consuming assays including micro-immunofluorescence, Western blotting or indirect immunofluorescence. For such pathogens, there is obviously still a need to identify antigens to establish a reliable, fast and high-throughput assay (Dupon et al. ). We evaluated two B. henselae proteins to develop a novel serological ELISA: a well-known antigen, the 17-kDa protein, and GroEL, identified during this study by a proteomic approach. When serum IgG were tested, the specificity and sensitivity were 76 and 65·7% for 17-kDa, respectively, and 82 and 42·9% for GroEL, respectively. IgM were found to be more sensitive and specific for both proteins: 17-kDa protein, specificity 86·2% and sensitivity 75%; GroEL, specificity 97·7% and sensitivity 45·3%. IgM antibodies were also measured in lymphoma patients and patients with Mycobacterium tuberculosis infection to assess the usefulness of our ELISA to distinguish them from B. henselae infected patients. The resulting specificities were 89·1 and 93·5% for 17-kDa protein and GroEL, respectively. Combining the results from the two tests, we obtained a sensitivity of 82·8% and a specificity of 83·9%. Our work described and validated a proteomic approach suitable to identify immunogenic proteins useful for developing a serological test of B. henselae infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

A reliable serological assay for the diagnosis of Cat Scratch Disease (CSD) - a pathological condition caused by Bartonella henselae infection - has not yet been developed. Such an assay would be extremely useful to discriminate between CSD and other pathologies with similar symptoms but different aetiologies, for example lymphoma or tuberculosis. We investigate the use of two B. henselae proteins - GroEL and 17-kDa - to develop a serological-based ELISA, showing promising results with the potential for further development as an effective tool for the differential diagnosing of B. henselae infection.

Hemin-binding proteins as potent markers for serological diagnosis of infections with Bartonella quintana

It is difficult to distinguish infections with different Bartonella species using commercially available immunofluorescence (indirect immunofluorescent antibody [IFA]) assay kits. To identify appropriate proteins for serodiagnosis of Bartonella quintana infections, we investigated the antigenicity of B. quintana proteins using sera from homeless people with high B. quintana IgG titers in IFA assay. These sera reacted strongly to an outer membrane protein, hemin-binding protein D (HbpD). Further, serum from an endocarditis patient infected with B. quintana reacted to HbpB and HbpD. To locate the antigenic sites within the proteins, we generated deletion mutants of HbpB and HbpD. Amino acid residues 89 to 220 of HbpB and 151 to 200 of HbpD were identified as the minimum regions required for recognition by these sera. Several oligopeptides comprising parts of the minimum regions of HbpB and HbpD were synthesized, and their immunoreactivity with the above-mentioned sera was tested by enzyme-linked immunosorbent assay (ELISA). Serum from the endocarditis patient reacted similarly to synthetic peptides HbpB2 (amino acid residues 144 to 173 of HbpB) and HbpD3 (151 to 200 residues of HbpD), while sera from the other subjects reacted to HbpD3. These results indicate that synthetic peptides HbpB2 and HbpD3 might be suitable for developing serological tools for differential diagnosis of B. quintana infections from other Bartonella infections.

Identification of candidate proteins for the diagnosis of Bartonella henselae infections using an immunoproteomic approach

Bartonella henselae is an emerging gram-negative facultative intracellular pathogen transmitted via Ctenocephalides felis (cat fleas) or cat scratches. Bartonellosis is present mainly in the form of cat scratch disease (CSD), bacillary angiomatosis and infective endocarditis (IE). The methods used to diagnose B. henselae rely on culturing, immunofluorescent assays and molecular techniques. The objective of the present study was to identify candidate proteins for the serodiagnosis of bartonellosis with the differential discrimination of both clinical scenarios: CSD and IE. For this, an immunoproteomic approach combined with 2-DE, immunoblotting and matrix-assisted laser desorption/ionization time-of-flight MS has been developed. Immunoproteomic profiles of sera collected from patients with CSD and IE were compared with those of blood donors. We identified several candidate proteins as phage-encoding Pap31 protein and an outer membrane protein of BH11510 that, in our view, might be useful for the serodiagnosis of bartonellosis.

Development of an immunoglobulin M capture-based enzyme-linked immunosorbent assay for diagnosis of acute infections with Bartonella henselae

We describe the development of an immunoglobulin M-specific enzyme-linked immunosorbent assay for the detection of an early antibody response to Bartonella henselae, the causative agent of cat scratch disease, bacillary angiomatosis, and endocarditis. This assay discriminates between B. henselae-positive and -negative patient samples with sensitivity and specificity values of 100% and 97.1%, respectively.

Discovery and analysis of Bartonella henselae antigens for use in clinical serologic assays

The antibody response to Bartonella henselae has been studied in a number of mammals; however, the human response needs to be further studied. After natural infection, humans have antibody reactivity to a large number of B. henselae proteins. We used a proteomic approach to identify antigenic proteins of B. henselae to determine their capacity to elicit a human antibody response. Comparing patient sera by Western blot analysis demonstrated significant amounts of reactivity to B. henselae. The immunofluorescence assay (IFA)-positive sera identified several protein spots of interest. However, a consistent reactivity to a single spot by all sera was not observed. Three of these spots demonstrated reactivity in 71%, 64%, and 64% of positive sera tested with negligible reactivity to the negative sera. These proteins were identified as GroES, BepA, and GroEL. Most IFA-positive sera demonstrated reactivity to GroES, GroEL, and BepA. The usefulness of these proteins for a clinical serologic assay is discussed.

Characterization of an immunogenic outer membrane autotransporter protein, Arp, of Bartonella henselae

Bartonella henselae is a recently recognized pathogenic bacterium associated with cat scratch disease, bacillary angiomatosis, and bacillary peliosis. This study describes the cloning, sequencing, and characterization of an antigenic autotransporter gene from B. henselae. A cloned 6.0-kb BclI-EcoRI DNA fragment expresses a 120-kDa B. henselae protein immunoreactive with 21.2% of sera from patients positive for B. henselae immunoglobulin G antibodies by indirect immunofluorescence, with 97.3% specificity and no cross-reactivity with antibodies against various other organisms. DNA sequencing of the clone revealed one open reading frame of 4,320 bp with a deduced amino acid sequence that shows homology to the family of autotransporters. The autotransporters are a group of proteins that mediate their own export through the outer membrane and consist of a passenger region, the alpha-domain, and an outer membrane transporter region, the beta-domain. The passenger domain shows homology to a family of pertactin-like adhesion proteins and contains seven, nearly identical 48-amino-acid repeats not found in any other bacterial or Bartonella DNA sequences. The passenger alpha-domain has a calculated molecular mass of 117 kDa, and the transporter beta-domain has a calculated molecular mass of 36 kDa. The clone expresses a 120-kDa protein and a protein that migrates at approximately 38 kDa exclusively in the outer membrane protein fraction, suggesting that the 120-kDa passenger protein remains associated with the outer membrane after cleavage from the 36-kDa transporter.

Cloning, characterization, and expression of Bartonella henselae p26

In order to identify immunoreactive Bartonella henselae proteins, B. henselae antiserum from an experimentally infected cat was used to screen a B. henselae genomic DNA expression library. One immunoreactive phage clone contained a gene (p26) with significant nucleotide identity with orthologs in brucellae, bartonellae, and several plant-associated bacteria. p26 gene sequences from four B. henselae strains, one B. koehlerae strain, and one B. clarridgeiae strain were cloned. Comparative nucleotide sequence analysis showed that p26 is a potential marker for molecular diagnosis of infection, as well as for identification to species level and genotyping of Bartonella sp. isolates. Alignment of the predicted amino acid sequences illustrated conserved putative protein features including a hydrophobic transmembrane region, a peptide cleavage site, and four dominant antigenic sites. Expression of p26 in Escherichia coli produced two proteins (26 and 27.5 kDa), both of which were reactive with feline anti-B. henselae antisera. Furthermore, murine hyperimmune serum raised against either recombinant protein reacted with both proteins. No reactivity to either recombinant protein was detected in nonimmune serum, and reactivity persisted as long as 20 weeks for one cat. The p26 protein product is an immunodominant antigen that is expressed during infection in cats as a preprotein and is subsequently cleaved to form mature P26.