Production of recombinant protein Pap31 and its application for the diagnosis of Bartonella bacilliformis infection

Bartonella henselae Recombinant Pap31 for the Diagnosis of Canine and Human Bartonelloses

Bartonella spp. comprise a genus of Gram-negative alphaproteobacteria that are slow growing, fastidious, and facultative intracellular pathogens with zoonotic potential. Immunofluorescent antibody assays (IFAs), Western blot (WB), and enzyme-linked immunosorbent assays (ELISAs), the frequently used modalities for the serological diagnosis of canine and human Bartonelloses, generate numerous false negative results. Therefore, the development of a reliable serodiagnostic assay for Bartonelloses is of clinical and epidemiological importance. Pap31, a heme binding surface protein of B. henselae, is associated with bacterial adhesion and related to bacterial colonization. To our knowledge, B. henselae Pap31 and its fragments (N-terminal (NTD), middle (MD), and C-terminal (CTD) domains) have not been investigated for the serodiagnosis of canine and human Bartonelloses. In this study, we evaluate the diagnostic utility of B. henselae recombinant whole Pap31 (rPap31) and Pap31 fragments by ELISA using sera from 70 dogs (36 Bartonella spp. IFA-positive (naturally infected), and 34 Bartonella spp. IFA- and PCR-negative (control dogs)) and 36 humans (18 Bartonella spp. IFA-positive (naturally infected) and 18 controls)). In the dogs, the area under the curve (AUC) score of recombinant whole Pap31 was 0.714 with a sensitivity of 42% and specificity of 94% at an OD cutoff value of 0.8955. Among the evaluated recombinant Pap31 proteins for the diagnosis of canine Bartonelloses, rPap31-NTD yielded the highest AUC score of 0.792 (95% CI 0.688-0.895) with a sensitivity of 44% and specificity of 100% at a cutoff value of 1.198. In concordance with this finding, rPap31-NTD also had the highest AUC score of 0.747 (95% CI 0.581-0.913) among the Pap31 recombinant proteins for the diagnosis of human Bartonelloses, with 39% sensitivity and 94% specificity at a cutoff value of 1.366. Recombinant whole Pap31 (rPap31) resulted in 72% sensitivity and 61% specificity at a cutoff value of 0.215 for human Bartonelloses. Due to either low sensitivity or questionable specificity, our findings indicate that recombinant Pap31 and the selected fragments may not be appropriate diagnostic targets in detecting anti-Bartonella antibodies in Bartonella-infected dogs and humans. The findings from this study can be used to further assess the antigenicity and immunogenicity of B. henselae Pap31 as a diagnostic target.

Immunogenic Peptides from Pap31 and SCS-α of Bartonella bacilliformis: One Step Closer to a Rapid Diagnostic Tool for Carrion's Disease

Bartonella bacilliformis is the causal agent of Carrion’s disease, an overlooked illness endemic in the Andean Mountains with Peru being the most affected country. The diagnostic of this illness is a challenge due to the limited resources and the common symptomatology with other infectious diseases. The goal of this study was to identify immunogenic peptides from Pap31 and succinyl-CoA synthetase α (SCS-α) of B. bacilliformis that might be suitable for developing a serologic tool. The immunodominant character of Pap31 and SCS-α was determined by Western blotting and in-silico analysis. Subsequently, 35 peptides were selected for epitope mapping and their immunoreactivity was tested by enzyme-linked immunosorbent assay (ELISA). A total of 30 sera were tested including pre-exposed people with high IgM levels for Pap31/SCS-α (23 sera), patients (2 sera) as well as 5 sera with no reactivity to Pap31/SCS-α. The results indicate that Pap31-8 (₁₈₇QAIGSAILKGTKDTGT₂₀₂) and SCS-α-12 (₅₉IFASVAEGKEKTGANA₇₄) are the most immunogenic peptides, with Pap31-8 showing potential to discriminate between B. bacilliformis and the remaining Bartonella spp., and SCS-α-12 differentiating Bartonella spp. from other microorganisms.

In silico analysis of Pap31 from Bartonella bacilliformis and other Bartonella spp

Pap31 is an outer membrane protein of Bartonella bacilliformis which is considered to be a potential antigenic candidate for the development of diagnostic tools. The present study aimed to compare Pap31 from B. bacilliformis with that of other Bartonella spp. The results showed the presence of at least 5 different B. bacilliformis Pap31 alleles, with the strain Ver097 being the most divergent (89.7% of identity with the reference strain KC583). The most significant finding was the presence of a variable number (1 to 3) of 6 amino acid tandem repeats (GTEGGG) in the different B. bacilliformis Pap31 alleles, with no similar structure in other established Bartonella spp., except for Bartonella ancashensis, another Bartonella spp. isolated from chronic cases of Carrion's disease. In both B. bacilliformis and B. ancashensis this repetitive region was coincident with the most predicted immunogenic region of the protein. In other microorganisms, the presence of amino acid tandem repeats has been related to the development of poorly functional antibodies. The findings of this study also suggest a utility of Pap31 amino acid tandem repeats as potential contributors to the immune evasion of Carrion's disease-related Bartonella spp. and the establishment of asymptomatic B. bacilliformis / B. ancashensis infections.

Carrion's disease: more than a neglected disease

Infections with Bartonella bacilliformis result in Carrion's disease in humans. In the first phase of infection, the pathogen causes a hemolytic fever ("Oroya fever") with case-fatality rates as high as ~90% in untreated patients, followed by a chronical phase resulting in angiogenic skin lesions ("verruga peruana"). Bartonella bacilliformis is endemic to South American Andean valleys and is transmitted via sand flies (Lutzomyia spp.). Humans are the only known reservoir for this old disease and therefore no animal infection model is available. In the present review, we provide the current knowledge on B. bacilliformis and its pathogenicity factors, vectors, possible unknown reservoirs, established and potential infection models and immunological aspects of the disease.

Seroprevalence and risk factors for infection with Bartonella bacilliformis in Loja province, Ecuador

The seroprevalence and epidemiology of Bartonella bacilliformis infection in the Andean highlands of Ecuador is largely unknown. We conducted a sero-epidemiologic survey of 319 healthy children aged 1-15 years living in six rural, mountain communities in Loja Province, Ecuador. Blood was collected by finger stick onto filter paper and dried, and the eluted sera analyzed for antibodies to B. bacilliformis by rPap31 ELISA. Demographic, entomologic, and household variables were assessed to investigate associated risk factors for antibody seropositivity to B. bacilliformis. Seroprevalence of 28% was found among children in the study communities. Increased risk of seropositivity was associated with the presence of lumber piles near houses. Decreased risk of seropositivity was observed with the presence of animal waste and incremental 100 meter increases in elevation. Although investigation of clinical cases of Carrion's disease was not within the scope of this study, our serology data suggest that infection of children with B. bacilliformis is prevalent in this region of Ecuador and is largely unrecognized and undiagnosed. This study highlights the need to further investigate the prevalence, pathogenesis, epidemiology, and disease impact of this pathogen in Ecuador.

Carrion's Disease: the Sound of Silence

Carrion's disease (CD) is a neglected biphasic vector-borne illness related to Bartonella bacilliformis. It is found in the Andean valleys and is transmitted mainly by members of the Lutzomyia genus but also by blood transfusions and from mother to child. The acute phase, Oroya fever, presents severe anemia and fever. The lethality is high in the absence of adequate treatment, despite the organism being susceptible to most antibiotics. Partial immunity is developed after infection by B. bacilliformis, resulting in high numbers of asymptomatic carriers. Following infection there is the chronic phase, Peruvian warts, involving abnormal proliferation of the endothelial cells. Despite potentially being eradicable, CD has been expanded due to human migration and geographical expansion of the vector. Moreover, in vitro studies have demonstrated the risk of the development of antimicrobial resistance. These findings, together with the description of new Bartonella species producing CD-like infections, the presence of undescribed potential vectors in new areas, the lack of adequate diagnostic tools and knowledge of the immunology and bacterial pathogenesis of CD, and poor international visibility, have led to the risk of increasing the potential expansion of resistant strains which will challenge current treatment schemes as well as the possible appearance of CD in areas where it is not endemic.

Succinyl-CoA Synthetase: New Antigen Candidate of Bartonella bacilliformis

Background

Bartonella bacilliformis is the causative agent of Carrion’s disease, a neglected illness with mortality rates of 40–85% in the absence of treatment. The lack of a diagnostic technique to overcome misdiagnosis and treat asymptomatic carriers is of note. This study aimed to identify new B. bacilliformis antigenic candidates that could lead to a new diagnostic tool able to be implemented in endemic rural areas.

Methodology/Principal Findings

Blood (n = 198) and serum (n = 177) samples were collected in northern Peru. Clinical data were recorded. Specific 16S rRNA amplification by RT-PCR, IFA and ELISA for IgM/IgG with whole cells as antigens was done. Western blot analysis and N-terminal amino acid sequencing detected seroreactive proteins. ELISAs for IgM/IgG for the antigenic candidates were performed. Of the population 33.3% reported at least one symptom compatible with Carrion’s disease; 25.4% (IFA), 27.1% (ELISA-IgG), 33.9% (ELISA-IgM) and 38.9% (RT-PCR) of samples were positive. Four proteins were considered potential antigenic candidates, including two new antigenic candidates, succinyl-CoA synthetase subunit α (SCS-α) and succinyl-CoA synthetase subunit β (SCS-β). On Western blot both Pap31 and SCS-α interacted with IgM, while GroEL and SCS-β interacted with IgG. The presence of specific antibodies against the antigenic candidates varied from 34.5% (IgG against SCS-α) to 97.2% (IgM against Pap31).

Conclusions/Significance

RT-PCR and the high levels of positivity for specific ELISAs demonstrate high levels of B. bacilliformis exposure and asymptomatic carriers among inhabitants. The new antigens identified might be used as a new rapid diagnostic tool to diagnose acute Carrion’s disease and identify asymptomatic carriers.

B. bacilliformis is a neglected pathogen causing Carrion’s disease, a febrile illness with two distinct phases, the acute so-called Oroya fever that can be life-threatening, and the chronic so-called Peruvian wart. This illness is currently limited to poor inhabitants of Andean valleys of Ecuador, Colombia and Peru and for this reason is understudied. One of the most significant limitations is the lack of an adequate diagnostic tool able to be implemented in rural areas. It is imperative to unequivocally detect cases of Carrion’s disease as well as identify asymptomatic carriers who perpetuate the illness. The present study describes the identification of 4 antigenic candidates potentially useful in the future development of a rapid diagnostic test. Moreover, 2 of these candidates have not been described in the literature. Additionally, four post-outbreak and one endemic community were studied and characterized. The identification of new antigens is essential for the development of a cheap, sensitive diagnostic tool, able to be implemented in low-income areas.

Proteins of Bartonella bacilliformis: Candidates for Vaccine Development

Bartonella bacilliformis is the etiologic agent of Carrión's disease or Oroya fever. B. bacilliformis infection represents an interesting model of human host specificity. The notable differences in clinical presentations of Carrión's disease suggest complex adaptations by the bacterium to the human host, with the overall objectives of persistence, maintenance of a reservoir state for vectorial transmission, and immune evasion. These events include a multitude of biochemical and genetic mechanisms involving both bacterial and host proteins. This review focuses on proteins involved in interactions between B. bacilliformis and the human host. Some of them (e.g., flagellin, Brps, IalB, FtsZ, Hbp/Pap31, and other outer membrane proteins) are potential protein antigen candidates for a synthetic vaccine.

Rapid and sensitive detection of Bartonella bacilliformis in experimentally infected sand flies by loop-mediated isothermal amplification (LAMP) of the Pap31 gene

Background

Carrion' disease, caused by Bartonella bacilliformis, remains truly neglected due to its focal geographical nature. A wide spectrum of clinical manifestations, including asymptomatic bacteremia, and lack of a sensitive diagnostic test can potentially lead to a spread of the disease into non-endemic regions where competent sand fly vectors may be present. A reliable test capable of detecting B. bacilliformis is urgently needed. Our objective is to develop a loop-mediated isothermal amplification (LAMP) assay targeting the pap31 gene to detect B. bacilliformis.

Methods and Findings

The sensitivity of the LAMP was evaluated in comparison to qPCR using plasmid DNA containing the target gene and genomic DNA in the absence and presence of human or sand fly DNA. The detection limit of LAMP was 1 to 10 copies/µL, depending on the sample metrics. No cross-reaction was observed when testing against a panel of various closely related bacteria. The utility of the LAMP was further compared to qPCR by the examination of 74 Lutzomyia longipalpis sand flies artificially fed on blood spiked with B. bacilliformis and harvested at days (D) 1, 3, 5, 7 and 9 post feeding. Only 86% of sand flies at D1 and 63% of flies at D3 were positive by qPCR. LAMP was able to detect B. bacilliformis in all those flies confirmed positive by qPCR. However, none of the flies after D3 were positive by either LAMP or qPCR. In addition to demonstrating the sensitivity of the LAMP assay, these results suggest that B. bacilliformis cannot propagate in artificially fed L. longipalpis.

Conclusions

The LAMP assay is as sensitive as qPCR for the detection of B. bacilliformis and could be useful to support diagnosis of patients in low-resource settings and also to identify B. bacilliformis in the sand fly vector.

Carrion's disease, caused by Bartonella bacilliformis remains truly neglected due to its focal geographical nature. A wide spectrum of clinical manifestations, including asymptomatic bacteremia can potentially lead to a spread of the disease into non-endemic regions. The PCR-based approach is sensitive for detection of B. bacilliformis but requires a thermocycler, thus limiting its use in remote endemic areas. LAMP is a simple method capable of detecting B. bacilliformis DNA within an hour under isothermal conditions, requiring less specialized equipment for amplification, thus enabling diagnosis in rural areas. This study demonstrated that the detection limit of LAMP, targeting the pap31 gene of B. bacilliformis, was comparable to that of qPCR. With a high, targeted selectivity, LAMP showed a high specificity as no cross-reaction was observed when testing a panel of closely related bacteria. The utility of the LAMP assay was further demonstrated by the examination of sand flies artificially fed on blood spiked with B. bacilliformis. The results showed that LAMP was able to detect B. bacilliformis in all flies confirmed positive by qPCR. This study showed that LAMP can be useful to support diagnosis of patients in low-resource settings and also to identify B. bacilliformis in the sand fly vector.

An evaluation study of enzyme-linked immunosorbent assay (ELISA) using recombinant protein Pap31 for detection of antibody against Bartonella bacilliformis infection among the Peruvian population

Reliable laboratory testing is of great importance to detect Bartonella bacilliformis infection. We evaluated the sensitivity and specificity of the enzyme-linked immunosorbent assay (ELISA) using recombinant protein Pap31 (rPap31) for the detection of antibodies against B. bacilliformis as compared with immunofluorescent assay (IFA). Of the 302 sera collected between 1997 and 2000 among an at-risk Peruvian population, 103 and 34 samples tested positive for IFA-immunoglobulin G (IgG) and IFA-IgM, respectively. By using Youden's index, the cutoff values of ELISA-IgG at 0.915 gave a sensitivity of 84.5% and specificity of 94%. The cutoff values of ELISA-IgM at 0.634 gave a sensitivity of 88.2% and specificity of 85.1%. Using latent class analysis, estimates of sensitivity and specificity of almost all the assays were slightly higher than those of a conventional method of calculation. The test is proved beneficial for discriminating between infected and non-infected individuals with the advantage of low-cost and high-throughput capability.

Peptide-based antibody detection for tuberculosis diagnosis

Tuberculosis (TB) is a major cause of morbidity and mortality, especially in developing countries. Despite significant limitations, microscopy remains the cornerstone of the global TB control strategy. As the TB epidemic escalates, new diagnostic methods that are accurate and also economical and simple to manufacture and deploy are urgently needed. Although several promising antigens have been identified and evaluated in recent years, the reproducible production of high-quality recombinant mycobacterial proteins with minimal batch-to-batch variation is difficult, laborious, and expensive. To determine the feasibility of devising a synthetic peptide-based diagnostic test for TB, we have delineated the immunodominant epitopes of three candidate antigens, Ag85B, BfrB, and TrxC, that were previously identified to be immunogenic in TB patients. The results demonstrate that combinations of carefully selected synthetic peptides derived from highly immunogenic proteins can be the basis for devising an immunodiagnostic test for TB.