Serologic diagnosis of tuberculosis using a simple commercial multiantigen assay

Serodiagnostic evaluation of fusion proteins from multiple antigens of Mycobacterium tuberculosis for active TB

Tuberculosis (TB) is a global health problem, being prevalent in the developing countries. A rapid, reliable and cost effective diagnostic method would help in controlling TB in the endemic populations. Development of suitable fusion molecules detecting multiple antibodies produced against Mycobacterium tuberculosis antigens would enhance sensitivity of serodiagnostic assays. In this study, EspC, CFP7 and PPE57 antigens of M. tuberculosis were selected for constructing fusion molecules after prediction of B-cell epitopes using in silico tools. Fusion proteins EspC-CFP7, HspX-EspC-CFP7 and HspX-EspC-CFP7-PPE57 were expressed in E.coli (BL21). The serodiagnostic potential of the individual antigens and their fusions was analyzed by screening 230 plasma samples of pulmonary TB patients. The single antigens HspX, EspC, CFP7, PPE57 showed sensitivities of 30%, 31%, 22% and 35%, respectively. The fusion protein EspC-CFP7 showed sensitivity of 43%. Linking of HspX antigen to the N-terminus of EspC-CFP7 fusion molecule increased sensitivity to 58%, while joining PPE57 antigen to the C-terminus of HspX-EspC-CFP7 increased sensitivity to 69%. The fusion protein HspX-EspC-CFP7-PPE57 seems to be a promising molecule for use in the development of fusions with higher sensitivity.

A scoping review on the field validation and implementation of rapid diagnostic tests for vector-borne and other infectious diseases of poverty in urban areas

BACKGROUND

Health personnel face challenges in diagnosing vector-borne and other diseases of poverty in urban settings. There is a need to know what rapid diagnostic technologies are available, have been properly assessed, and are being implemented to improve control of these diseases in the urban context. This paper characterizes evidence on the field validation and implementation in urban areas of rapid diagnostics for vector-borne diseases and other diseases of poverty.

MAIN BODY

A scoping review was conducted. Peer-reviewed and grey literature were searched using terms describing the targeted infectious diseases, diagnostics evaluations, rapid tests, and urban setting. The review was limited to studies published between 2000 and 2016 in English, Spanish, French, and Portuguese. Inclusion and exclusion criteria were refined post hoc to identify relevant literature regardless of study design and geography. A total of 179 documents of the 7806 initially screened were included in the analysis. Malaria (n = 100) and tuberculosis (n = 47) accounted for the majority of studies that reported diagnostics performance, impact, and implementation outcomes. Fewer studies, assessing mainly performance, were identified for visceral leishmaniasis (n = 9), filariasis and leptospirosis (each n = 5), enteric fever and schistosomiasis (each n = 3), dengue and leprosy (each n = 2), and Chagas disease, human African trypanosomiasis, and cholera (each n = 1). Reported sensitivity of rapid tests was variable depending on several factors. Overall, specificities were high (> 80%), except for schistosomiasis and cholera. Impact and implementation outcomes, mainly acceptability and cost, followed by adoption, feasibility, and sustainability of rapid tests are being evaluated in the field. Challenges to implementing rapid tests range from cultural to technical and administrative issues.

CONCLUSIONS

Rapid diagnostic tests for vector-borne and other diseases of poverty are being used in the urban context with demonstrated impact on case detection. However, most evidence comes from malaria rapid diagnostics, with variable results. While rapid tests for tuberculosis and visceral leishmaniasis require further implementation studies, more evidence on performance of current tests or development of new alternatives is needed for dengue, Chagas disease, filariasis, leptospirosis, enteric fever, human African trypanosomiasis, schistosomiasis and cholera.

Fusion Molecules of Heat Shock Protein HSPX with Other Antigens of Mycobacterium tuberculosis Show High Potential in Serodiagnosis of Tuberculosis

Variable individual response against the antigens of Mycobacterium tuberculosis necessitates detection of multiple antibodies for enhancing reliability of serodiagnosis of tuberculosis. Fusion molecules consisting of two or more antigens showing high sensitivity would be helpful in achieving this objective. Antigens of M. tuberculosis HSPX and PE35 were expressed in a soluble form whereas tnPstS1 and FbpC1 were expressed as inclusion bodies at 37°C. Heat shock protein HSPX when attached to the N-termini of the antigens PE35, tnPstS1 and FbpC1, all the fusion molecules were expressed at high levels in E. coli in a soluble form. ELISA analysis of the plasma samples of TB patients against HSPX-tnPstS1 showed 57.7% sensitivity which is nearly the same as the expected combined value obtained after deducting the number of plasma samples (32) containing the antibodies against both the individual antigens. Likewise, the 54.4% sensitivity of HSPX-PE35 was nearly the same as that expected from the combined values of the contributing antigens. Structural analysis of all the fusion molecules by CD spectroscopy showed that α-helical and β-sheet contents were found close to those obtained through molecular modeling. Molecular modeling studies of HSPX-tnPstS1 and HSPX-PE35 support the analytical results as most of the epitopes of the contributing antigens were found to be available for binding to the corresponding antibodies. Using these fusion molecules in combination with other antigenic molecules should reduce the number of antigenic proteins required for a more reliable and economical serodiagnosis of tuberculosis. Also, HSPX seems to have potential application in soluble expression of heterologous proteins in E. coli.

Improving acid-fast fluorescent staining for the detection of mycobacteria using a new nucleic acid staining approach

Acid fast staining of sputum smears by microscopy remains the prevalent method for detecting Mycobacterium tuberculosis. The sensitivity of microscopy using acid fast stains requires 10(4) bacilli per ml of sputum. Although fluorescent acid fast stains, such as Auramine-O, show improved sensitivity, almost half of culture-positive TB cases are currently estimated to remain smear-negative. These current diagnosis problems provide impetus for improving staining procedures. We evaluated a novel fluorescent acid-fast staining approach using the nucleic acid-binding dye SYBR(®) Gold on mycobacterial in vitro cultures. The SYBR(®) Gold stain detected 99% of MTB in both actively replicating aerobic and non-replicating hypoxic cultures. Transmission light microscopy with Ziehl-Neelsen fuchsin, and fluorescence microscopy with Auramine-O or Auramine-rhodamine detected only 54%-86% of MTB bacilli. SYBR(®) Gold fluoresces more intensely than Auramine-O, and is highly resistant to fading. The signal to noise ratio is exceptionally high due to a >1000-fold enhanced fluorescence after binding to DNA/RNA, thereby reducing most background fluorescence. Although cost and stability of the dye may perhaps limit its clinical use at this time, these results warrant further research into more nucleic acid dye variants. In the meantime, SYBR(®) Gold staining shows great promise for use in numerous research applications.

Expression, purification and improved antigenicity of the Mycobacterium tuberculosis PstS1 antigen for serodiagnosis

The phosphate-specific transport substrate binding protein-1 (PstS1) is a potential antigen used for the serological diagnosis of tuberculosis. For a highly specific diagnostic result, it is important that the recombinant PstS1 be highly pure and correctly folded. In this study, the PstS1 was expressed as fusion protein with glutathione-S-transferase (PstS1-GST) and Escherichia coli trigger factor (PstS1-TF) and their immunodiagnostic potentials were evaluated. The insoluble PstS1-GST was denatured and refolded to the native conformation by a step-gradient dilution, followed by purification with affinity chromatography on immobilized glutathione whereas the soluble PstS1-TF was directly purified by Ni-NTA affinity and size-exclusion chromatographies. The levels of antibody responses to PstS1-TF and PstS1-GST were measured by enzyme-linked immunosorbent assay (ELISA) in the sera of 22 tuberculosis patients with smear-positive and culture-positive tuberculosis as well as 20 healthy individuals; the antigenicities of the samples were evaluated in terms of sensitivity and specificity. To determine the diagnostic accuracy, receiver operation characteristic (ROC) curves were constructed and then the areas under the ROC curves (AUC) were calculated; the AUC values for PstS1-TF and PstS1-GST were 0.971 and 0.877 with 95% confidence intervals (CI) of 0.927-1.000 and 0.768-0.986, respectively. The specificity of PstS1-TF was reduced from 89.5% to 84.2%, but in case of PstS1-GST it dropped drastically from 78.9% to 26.3% when the sensitivity was raised from 86.4% up to 95.5%. These results indicate that PstS1-TF is capable of producing more accurate and consistent serodiagnostic results than PstS1-GST, possibly due to its conformation being closer to the native state.

Opportunities for improved serodiagnosis of human tuberculosis, bovine tuberculosis, and paratuberculosis

Mycobacterial infections—tuberculosis (TB), bovine tuberculosis (bTB), and Johne's disease (JD)—are major infectious diseases of both human and animals. Methods presently in use for diagnosis of mycobacterial infections include bacterial culture, nucleic acid amplification, tuberculin skin test, interferon-γ assay, and serology. Serological tests have several advantages over other methods, including short turn-around time, relatively simple procedures, and low cost. However, current serodiagnostic methods for TB, bTB and JD exhibit low sensitivity and/or specificity. Recent studies that have aimed to develop improved serodiagnostic tests have mostly focused on identifying useful species-specific protein antigens. A review of recent attempts to improve diagnostic test performance indicates that the use of multiple antigens can improve the accuracy of serodiagnosis of these mycobacterial diseases. Mycobacteria also produce a variety of species-specific nonprotein molecules; however, only a few such molecules (e.g., cord factor and lipoarabinomannan) have so far been evaluated for their effectiveness as diagnostic antigens. For TB and bTB, there has been recent progress in developing laboratory-free diagnostic methods. New technologies such as microfluidics and “Lab-on-Chip” are examples of promising new technologies that can underpin development of laboratory-free diagnostic devices for these mycobacterial infections.

Diagnostic value of an immunochromatographic test over clinical predictors for tuberculosis in HIV patients

Purpose:

The value of an immunochromatographic test for tuberculosis (ICT-TB) combined with clinical predictors has yet to be evaluated in Thailand. This study aimed to assess any additional diagnostic value of an ICT-TB test over that of clinical predictors in a group of human immunodeficiency virus (HIV) patients as well as in subgroups of HIV patients classified by clinical risk scores.

Patients and methods:

An extended cross-sectional study was conducted at a community hospital in Chiang Rai and a general hospital in Lampang. HIV patients registered between April 2009 and May 2010 were screened by a locally made ICT-TB test, including 38, 16, and 6 kD Microbacterium tuberculosis antigens, as well as by routine evaluations for TB diagnosis. Demographic data, medical history, signs, and symptoms were recorded. Participants were followed up for 2 months for final ascertainment of TB diagnosis.

Results:

Of 206 patients, 37 (18%) had TB. Four clinical predictors were identified: low body mass index (<19 kg/m²), prolonged cough (duration >2 weeks), shaking chills (≥1 week), and no use of antiretrovirals. The area under the receiver operating curve was 90.2%; adding the ICT-TB test result increased the area nonsignificantly to 91.6% (P = 0.40). When patients were categorized by risk scores derived from selected clinical predictors into low (scores ≤7) and high (scores >7) TB risk groups, a positive ICT-TB test increased the positive predictive value nonsignificantly in the low risk group (from 12.5% to 27.3%, P = 0.17) and the high risk group (from 78.6% to 80.8%, P = 0.73).

Conclusion:

In this study setting, the ICT-TB test did not enhance TB diagnosis over the four clinical predictors in the overall group or any subgroups of HIV patients classified by clinical risk scores.

Validation of the ALS assay in adult patients with culture confirmed pulmonary tuberculosis

Background

We have earlier shown that Bacille Calmette-Guérin (BCG) vaccine-specific IgG Antibodies in Lymphocyte Supernatant (ALS) can be used for diagnosis of active tuberculosis (TB) in adults and children.

Methodology/Principal Findings

The ALS method was validated in a larger cohort (n = 212) of patients with suspicion of pulmonary TB using multiple antigens (BCG, LAM, TB15.3, TB51A, CFP10-ESAT6-A, CFP, CW) from Mycobacterium tuberculosis. The sensitivity and specificity of the ALS assay was calculated using non-TB patients as controls. The sensitivity and the specificity were highest with BCG vaccine (90% and 88% respectively) followed by LAM (89% and 87% respectively). Simultaneous assessment of multiple antigen-specific antibodies increased sensitivity (91%) and specificity (88%). Using higher lymphocyte count in smaller volume of culture media increased detection and reduced the assay duration to ∼30 hrs. Twenty one patients with clinical findings strongly suggestive of TB finally diagnosed as non-TB patients were positive by the ALS assay, of which 9 (43%) were positive for 7 antigens and 19 (90%) for at least 3 antigens.

Conclusions/Significance

Our findings show that simultaneous detection of antigens improves the diagnostic potential of the ALS assay; the modified method increases sensitivity and can provide results in <48 hours, and enable detection of some cases of pulmonary TB that are not detectable by standard methods.

Facing the crisis: improving the diagnosis of tuberculosis in the HIV era

Although the human immunodeficiency virus (HIV) infection pandemic has had a catastrophic impact on tuberculosis (TB) control efforts, especially in sub-Saharan Africa, most of the fundamental concepts reflected in the directly observed treatment, short course (DOTS) strategy still hold true in the HIV era. What has changed, and dramatically, is the importance of speedy and accurate TB diagnosis and the difficulty of achieving this. The disproportionate amount of smear-negative disease in sub-Saharan Africa, which shoulders two-thirds of the global burden of HIV infection and acquired immunodeficiency syndrome, has greatly complicated TB case detection and disease control. Now, 15 years after TB rates began to soar in countries where HIV infection is prevalent, we have learned that the conventional approach -- passively waiting for patients with advanced symptomatic disease to make their way to microscopy centers for diagnosis -- has disastrous consequences. Without better diagnostic tools for TB and effective strategies for their implementation, transmission will not be interrupted, mortality will not be checked, and TB will not be controlled in areas where HIV infection is prevalent. Fortunately, a number of technical opportunities exist for the creation of improved diagnostic tests. Developing and exploiting such tests to support TB control in HIV-infected populations is an urgent priority. A substantial public sector effort is under way to work in partnership with the biotechnology industry to accelerate progress toward that goal. In this article, we will define the need for better TB tests and describe technologies being developed to meet that need.

PrimaTB STAT-PAK assay, a novel, rapid lateral-flow test for tuberculosis in nonhuman primates

Tuberculosis (TB) is the most important zoonotic bacterial disease in nonhuman primates (NHP). The current diagnostic method, the intradermal palpebral tuberculin test, has serious shortcomings. We characterized antibody responses in NHP against Mycobacterium tuberculosis to identify immunodominant antigens and develop a rapid serodiagnostic test for TB. A total of 422 NHP were evaluated, including 243 rhesus (Macaca mulatta), 46 cynomolgus (Macaca fascicularis), and 133 African green (Cercopithecus aethiops sabaeus) monkeys at five collaborative centers. Of those, 50 monkeys of the three species were experimentally inoculated with M. tuberculosis. Antibody responses were monitored every 2 to 4 weeks for up to 8 months postinfection by MultiAntigen Print ImmunoAssay with a panel of 12 recombinant antigens. All of the infected monkeys produced antibodies at various levels and with different antigen recognition patterns. ESAT-6 and MPB83 were the most frequently recognized proteins during infection. A combination of selected antigens which detected antibodies in all of the infected monkeys was designed to develop the PrimaTB STAT-PAK assay by lateral-flow technology. Serological evaluation demonstrated high diagnostic sensitivity (90%) and specificity (99%). The highest rate of TB detection was achieved when the skin test was combined with the PrimaTB STAT-PAK kit. This novel immunoassay provides a simple, rapid, and accurate test for TB in NHP.

Evaluation of Mycobacterium tuberculosis--specific antibody responses in populations with different levels of exposure from Tanzania, Ethiopia, Brazil, and Denmark

BACKGROUND

New, simple, and better-performing diagnostic tools are needed for the diagnosis of tuberculosis (TB). Much effort has been invested in developing an antibody-based test for TB, but to date, no such test has performed with sufficient sensitivity and specificity. A key question remaining is the extent to which the disappointing performance of current tests is associated with a high background prevalence of latent TB.

METHODS

We compared Mycobacterium tuberculosis-specific ESAT-6 and CFP-10 antibody responses in a total of 565 human serum samples from M. tuberculosis-uninfected donors and donors with latent infection, as well as samples from patients with active TB. Our study included samples from 4 countries, representing environments with low, intermediate, and high TB incidences.

RESULTS

We demonstrated significant increases in antibody levels in latently infected contacts, compared with M. tuberculosis-uninfected individuals, and in patients with active TB disease, compared with latently infected contacts. Furthermore, we found a striking increase in the magnitude of the antibody responses in samples obtained from infected Ethiopian individuals (with and without disease), compared with Danish and Brazilian infected individuals; this was presumably the result of higher exposure levels.

CONCLUSIONS

Our study confirms the presence of ESAT-6 and CFP-10 antibodies in patients with TB, and we demonstrate that significant antibody responses are not restricted to active TB disease but can reflect latent infection, particularly in areas with high levels of exposure to M. tuberculosis. This finding is important for the understanding of the poor discriminatory power of current serodiagnostic tests in regions of endemicity, and it may have major implications on the future development of serologic tests.

Current issues on molecular and immunological diagnosis of tuberculosis

Laboratory diagnosis of tuberculosis (TB) traditionally relies on smear microscopy and culture of Mycobacterium tuberculosis from clinical samples. With recent advances in technology, there have been numerous efforts to develop new diagnostic tests for TB that overcome the low sensitivity and specificity and long turnover time associated with current diagnostic tests. Molecular biological tests based on nucleic acid amplification have brought an unprecedented opportunity for the rapid and specific detection of M. tuberculosis from clinical specimens. With automated sequencing analysis, species identification of mycobacteria is now easier and more accurate than with conventional methods, and rapid detection of mutations in the genes associated with resistance to TB drugs provides early information on the potential drug resistance for each clinical isolate or for clinical samples. In addition, immunological tests for the detection of M. tuberculosis antigens and antibodies to the antigens have been explored to identify individuals at risk of developing TB or with latent TB infection (LTBI). The recent introduction of commercial IFN-gamma assay kits for the detection of LTBI provides a new approach for TB control even in areas with a high incidence of TB. However, these molecular and immunological tools still require further evaluation using large scale cohort studies before implementation in TB control programs.

Commercial serological antibody detection tests for the diagnosis of pulmonary tuberculosis: a systematic review

BACKGROUND

The global tuberculosis epidemic results in nearly 2 million deaths and 9 million new cases of the disease a year. The vast majority of tuberculosis patients live in developing countries, where the diagnosis of tuberculosis relies on the identification of acid-fast bacilli on unprocessed sputum smears using conventional light microscopy. Microscopy has high specificity in tuberculosis-endemic countries, but modest sensitivity which varies among laboratories (range 20% to 80%). Moreover, the sensitivity is poor for paucibacillary disease (e.g., pediatric and HIV-associated tuberculosis). Thus, the development of rapid and accurate new diagnostic tools is imperative. Immune-based tests are potentially suitable for use in low-income countries as some test formats can be performed at the point of care without laboratory equipment. Currently, dozens of distinct commercial antibody detection tests are sold in developing countries. The question is "do they work?"

METHODS AND FINDINGS

We conducted a systematic review to assess the accuracy of commercial antibody detection tests for the diagnosis of pulmonary tuberculosis. Studies from all countries using culture and/or microscopy smear for confirmation of pulmonary tuberculosis were eligible. Studies with fewer than 50 participants (25 patients and 25 control participants) were excluded. In a comprehensive search, we identified 68 studies. The results demonstrate that (1) overall, commercial tests vary widely in performance; (2) sensitivity is higher in smear-positive than smear-negative samples; (3) in studies of smear-positive patients, Anda-TB IgG by enzyme-linked immunosorbent assay shows limited sensitivity (range 63% to 85%) and inconsistent specificity (range 73% to 100%); (4) specificity is higher in healthy volunteers than in patients in whom tuberculosis disease is initially suspected and subsequently ruled out; and (5) there are insufficient data to determine the accuracy of most commercial tests in smear microscopy-negative patients, as well as their performance in children or persons with HIV infection.

CONCLUSIONS

None of the commercial tests evaluated perform well enough to replace sputum smear microscopy. Thus, these tests have little or no role in the diagnosis of pulmonary tuberculosis. Lack of methodological rigor in these studies was identified as a concern. It will be important to review the basic science literature evaluating serological tests for the diagnosis of pulmonary tuberculosis to determine whether useful antigens have been described but their potential has not been fully exploited. Activities leading to the discovery of new antigens with immunodiagnostic potential need to be intensified.

Identification of diagnostic markers for tuberculosis by proteomic fingerprinting of serum

BACKGROUND

We investigated the potential of proteomic fingerprinting with mass spectrometric serum profiling, coupled with pattern recognition methods, to identify biomarkers that could improve diagnosis of tuberculosis.

METHODS

We obtained serum proteomic profiles from patients with active tuberculosis and controls by surface-enhanced laser desorption ionisation time of flight mass spectrometry. A supervised machine-learning approach based on the support vector machine (SVM) was used to obtain a classifier that distinguished between the groups in two independent test sets. We used k-fold cross validation and random sampling of the SVM classifier to assess the classifier further. Relevant mass peaks were selected by correlational analysis and assessed with SVM. We tested the diagnostic potential of candidate biomarkers, identified by peptide mass fingerprinting, by conventional immunoassays and SVM classifiers trained on these data.

FINDINGS

Our SVM classifier discriminated the proteomic profile of patients with active tuberculosis from that of controls with overlapping clinical features. Diagnostic accuracy was 94% (sensitivity 93.5%, specificity 94.9%) for patients with tuberculosis and was unaffected by HIV status. A classifier trained on the 20 most informative peaks achieved diagnostic accuracy of 90%. From these peaks, two peptides (serum amyloid A protein and transthyretin) were identified and quantitated by immunoassay. Because these peptides reflect inflammatory states, we also quantitated neopterin and C reactive protein. Application of an SVM classifier using combinations of these values gave diagnostic accuracies of up to 84% for tuberculosis. Validation on a second, prospectively collected testing set gave similar accuracies using the whole proteomic signature and the 20 selected peaks. Using combinations of the four biomarkers, we achieved diagnostic accuracies of up to 78%.

INTERPRETATION

The potential biomarkers for tuberculosis that we identified through proteomic fingerprinting and pattern recognition have a plausible biological connection with the disease and could be used to develop new diagnostic tests.

Poor performance of a novel serological test for diagnosis of pulmonary tuberculosis in Bangui, Central African Republic

We assessed the performance of a serological test for tuberculosis (SDHO Laboratories Inc., Canada) in our setting. Among 68 of 99 suspected pulmonary tuberculosis patients who were scored as having tuberculosis on the basis of Mycobacterium tuberculosis-positive culture, the sensitivity of the serological test was lower than that of sputum smear microscopic examination (20.6% versus 80.9%, respectively; P < 0.000001).

A cocktail of affinity-purified antibodies reactive with diagnostically useful mycobacterial antigens ES-31, ES-43, and EST-6 for detecting the presence of Mycobacterium tuberculosis

A cocktail of affinity-purified antibodies against diagnostically useful Mycobacterium tuberculosis H37Ra excretory-secretory protein antigens ES-31, ES-43, and EST-6 was explored for detection of circulating free and immune-complexed (IC) antigen in sera of patients with confirmed tuberculosis (TB) by sandwich enzyme-linked immunosorbent assay and compared with monospecific anti-ES-31 antibody. Out of 68 smear-positive TB cases studied, using cocktail antibody, a sensitivity of 97% (66/68) for immune-complexed cocktail antigen and 91% (62/68) for free cocktail-antigen detection was observed, compared to 91% (62/68) for immune-complexed ES-31 and 79% (54/68) for free ES-31 antigen when anti-ES-31 antibody was used alone. Thus, combinatorial use of antibodies showed improved sensitivity and was thus observed to be better than single antibody. The specificity was observed to be 99% for immune-complexed antigen using cocktail antibody. Furthermore, analysis of different groups of TB sera showed that circulating immune-complexed antigen is a sensitive marker than free antigen.

Evaluation of the ICT Tuberculosis test for the routine diagnosis of tuberculosis

BACKGROUND

Rapid and accurate diagnosis of tuberculosis (TB) is crucial to facilitate early treatment of infectious cases and thus to reduce its spread. To improve the diagnosis of TB, more rapid diagnostic techniques such as antibody detection methods including enzyme-linked immunosorbent assay (ELISA)-based serological tests and immunochromatographic methods were developed. This study was designed to evaluate the validity of an immunochromatographic assay, ICT Tuberculosis test for the serologic diagnosis of TB in Antalya, Turkey.

METHODS

Sera from 72 patients with active pulmonary (53 smear-positive and 19 smear-negative cases) and eight extrapulmonary (6 smear-positive and 2 smear-negative cases) TB, and 54 controls from different outpatient clinics with similar demographic characteristics as patients were tested by ICT Tuberculosis test.

RESULTS

The sensitivity, specificity, and negative predictive value of the ICT Tuberculosis test for pulmonary TB were 33.3%, 100%, and 52.9%, respectively. Smear-positive pulmonary TB patients showed a higher positivity rate for antibodies than smear-negative patients, but the difference was not statistically significant. Of the eight patients with extrapulmonary TB, antibody was detected in four patients.

CONCLUSION

Our results suggest that ICT Tuberculosis test can be used to aid TB diagnosis in smear-positive patients until the culture results are available.

Expression and purification of recombinant 38-kDa and Mtb81 antigens of Mycobacterium tuberculosis for application in serodiagnosis

Availability of genome sequence of Mycobacterium tuberculosis has accelerated identification of antigens for serodiagnosis of tuberculosis and a number of new antigens are being tested in various combinations to produce cocktails with high sensitivity and specificity. For producing a highly specific diagnostic test, it is important that the recombinant antigens be highly pure, free of host protein, and correctly folded so that they bind only to specific antibodies. Also, for commercial viability they need to be produced in high yields. We have cloned, expressed, and purified a number of mycobacterial antigens in Escherichia coli. This paper describes, expression and purification of two important mycobacterial proteins with serodiagnostic potential, namely, 38-kDa and Mtb81 antigens, in monomeric form. The protocol involves using a T7 promoter based expression vector under conditions of regulated and slow expression followed by three-step column chromatography procedure to obtain highly purified proteins. The yields of the two proteins were several folds higher than previously reported. The purified proteins were useful in detecting antibodies in sera of tuberculosis patients (smear positive, smear negative, and extra-pulmonary categories).

Prognostic variables for high titres in a fluorescent antibody test to diagnose tuberculosis

SETTING

The four hospitals and a tuberculosis clinic in the province of Zeeland, The Netherlands.

OBJECTIVE

To assess the usefulness of PPD antibody measurement in the diagnosis of tuberculosis in patients admitted to hospital.

PATIENTS AND METHODS

Sixty-one patients presenting with active tuberculosis, and 215 control patients were included in the study. Initial serum PPD antibody titres were determined with a macrophage uptake Fluorescent antibody test (MuFat) to construct a discrimination model between Tuberculosis (TB) and non-TB. We also retrospectively collected clinical parameters of the TB patients at presentation. Univariate and multivariate logistic regression are used to identify variables predicting high antibody titres.

RESULTS

In TB patients, the presence of clinical symptoms (OR=10.63) and the presence of at least two concurrent non-lymph node disease localizations outside thorax and abdomen (OR=13.94) are necessary and sufficient to predict high titres. The logistic model shows a significant contribution of the 2log (titre) to the discrimination between TB and non-TB patients. At a cut-off value of 128, a specificity, sensitivity, and positive predictive and negative predictive values of 97%, 39%, 80% and 85%, respectively, are calculated in the study cohort.

CONCLUSION

Our data suggest an application of the test at high cut-off values for timely diagnosis of difficult-to-diagnose TB patients. The results of this retrospective study will have to be confirmed in further prospective studies.

Assessing the serodiagnostic potential of 35 Mycobacterium tuberculosis proteins and identification of four novel serological antigens

Improved diagnostic reagents are needed for the detection of Mycobacterium tuberculosis infections, and the development of a serodiagnostic test would complement presently available diagnostic methods. The aim of the present study was to identify novel serological targets for use for the future serodiagnosis of tuberculosis (TB). We cloned and expressed 35 M. tuberculosis proteins as recombinant proteins in Escherichia coli and analyzed their serodiagnostic potentials. By a two-step selection process, four superior seroantigens, TB9.7, TB15.3, TB16.3, and TB51, were identified, none of which has been described before. The four novel antigens were tested with panels of sera from smear-positive and smear-negative TB patients from areas both where TB is endemic and where TB is not endemic, with recognition frequencies ranging from 31 to 93% and with a specificity of at least 97%. The single most potent antigen was TB16.3, which had a sensitivity of 48 to 55% with samples from Danish resident TB patients and a sensitivity of 88 to 98% with samples from African TB patients. Importantly, the TB16.3 and the TB9.7 antigens were recognized by more than 85% of the samples from TB patients coinfected with human immunodeficiency virus, a patient group for which it is in general difficult to detect M. tuberculosis-specific antibodies.

Childhood tuberculosis and its early diagnosis

Traditional methods for laboratory diagnosis of tuberculosis are unsatisfactory, especially for children, in whose specimens mycobacteria are usually sparse. Recent changes in tuberculosis epidemiology in developed countries, including a large increase in incidence in children from certain ethnic minorities, have prompted interest in newer diagnostic methods. Liquid-based culture detection systems offer improved sensitivity and speed of diagnosis, although the time taken for detection of growth is still upwards of 1 week. Nucleic acid amplification techniques offer more rapid results, but perform best on smear-positive samples; sensitivities may be as low as 50% in smear-negative specimens. Although these newer techniques are widely used in some developed countries, in others, they are not perceived as offering sufficient benefit to justify their routine use. The diagnostic accuracy of mycobacteriophage and serologic methods is insufficient to justify their wide use even in developing countries. Despite recent developments, there is still no panacea for diagnosis of childhood tuberculosis.

A review of tuberculosis: reflections on the past, present and future of a global epidemic disease

Tuberculosis remains the leading cause of death worldwide from a single infectious organism. Approximately 32% of the world's population is infected and an estimated two million people die annually from this treatable disease. Over the past 50 years, with medical treatment and standard public health practices, tuberculosis diminished in developed countries and resulted in a loss of interest and funding for research in improving diagnostic and treatment options. In developing countries, efforts including BCG vaccination have failed to control tuberculosis and the disease continues to spread as the world becomes more globalized. At the same time, multidrug resistant tuberculosis has emerged, challenging even the most advance treatment centers. Better diagnostic techniques, control measures and treatment options are desperately needed but advances require worldwide commitment to battle this age-old disease.

Recent tuberculosis advances in Latin America

PURPOSE OF REVIEW

Tuberculosis kills more people than any other infection. Despite advances in diagnostic methods and greater understanding of the reasons for treatment failure, tuberculosis remains common throughout Latin America.

RECENT FINDINGS

The impact of HIV and multidrug resistance on tuberculosis control has been enormous. HIV-positive patients may be at 10 times greater risk of multidrug resistant tuberculosis than HIV-negative patients. Hopefully, improved diagnostic techniques will allow more rapid diagnosis of tuberculosis and new colorimetric systems are being developed that will enable expedited drug-sensitivity testing. However, in alarming reports, only 58% of patients were treated with the recommended treatment regime in a Brazilian study, and dropout from treatment in parts of Bolivia was common. Many failings could be combated by rigorous education of patients and physicians. In an encouraging advance, multidrug resistant tuberculosis was successfully treated in a community-based programme, saving an estimated 90% of the cost of hospital-based treatment. An opportunity to identify treatment failure earlier is demonstrated by the finding that 2 months after the initiation of therapy, positive smears were found in only 3% of those whose treatment was successful, but 74% of those whose treatment failed.

SUMMARY

The importance of inexpensive and widely available drugs to treat HIV and multidrug resistant tuberculosis in Latin America is clear. The need for rapid, affordable tests for tuberculosis diagnosis, and for easy drug sensitivity testing is also evident. Finally, improving treatment success is achievable even in the resource poor setting.

Mycobacterium tuberculosis (Mtb) isocitrate dehydrogenases show strong B cell response and distinguish vaccinated controls from TB patients

Proteins released from Mycobacterium tuberculosis (Mtb) during late logarithmic growth phase are often considered candidate components of immunogenic or autolysis markers. One such protein is isocitrate dehydrogenase (ICD), a key regulatory enzyme in the citric acid cycle. We have evaluated the immunogenic properties of two isoforms of Mtb ICD and compared them with the control antigens heat-shock protein 60 and purified protein derivative (PPD). PPD lacks the sensitivity to distinguish between bacillus Calmette-Guérin (BCG)-vaccinated and tuberculosis (TB)-infected populations, and, therefore, epidemiological relevance of PPD in BCG-vaccinated regions is debatable. We show that Mtb ICDs elicit a strong B cell response in TB-infected populations and can differentiate between healthy BCG-vaccinated populations and those with TB. The study population (n = 215) was categorized into different groups, namely, patients with fresh infection (n = 42), relapsed TB cases (n = 32), patients with extrapulmonary TB (n = 35), clinically healthy donors (n = 44), nontuberculous mycobacteria patients (n = 30), and non-TB patients (culture negative for acid-fast bacteria but carrying other infections, n = 32). The Mtb ICDs showed statistically significant antigenic distinction between healthy BCG-vaccinated controls and TB patients (P < 0.0001) and those with other infections. Although extrapulmonary infections could not be discriminated from healthy controls by heat-shock protein 60 (P = 0.2177), interestingly, the Mtb ICDs could significantly (P < 0.0001) do so. Our results highlight the immunodominant, immunosensitive, and immunospecific nature of Mtb ICDs and point to an unusual property of this tricarboxylic acid energy cycle enzyme.

Immunoglobulin A (IgA) and IgG immune responses against P-90 antigen for diagnosis of pulmonary tuberculosis and screening for Mycobacterium tuberculosis infection

The purpose of the present study was to evaluate the usefulness of detection of serum immunoglobulin A (IgA) and IgG antibodies directed against the mycobacterial P-90 antigen for the diagnosis of active pulmonary tuberculosis (PTB) among symptomatic individuals and for the detection of Mycobacterium tuberculosis infections among close contacts of PTB patients. Two commercially available enzyme immunoassay (EIA) kits (IgA EIA-TB [EIA-IgA] and IgG EIA-TB [EIA-IgG]; Kreatech Diagnostics) were evaluated in a blinded fashion by using stored serum samples from 268 individuals, including 69 patients with PTB, 41 patients with diseases other than tuberculosis (TB), 12 subjects with healed PTB, 39 close contacts of PTB patients, and 107 healthy volunteers. For the EIA-IgA, the sensitivity was 74% and the specificity was 68% when a cutoff determined by a receiver operator characteristic curve was used. For the EIA-IgG, the sensitivity was 69% and the specificity was 64%. The EIA-IgA was positive for 54% of healthy close contacts of PTB patients but only 8% of healthy controls without contact with a PTB patient or a prior personal history of TB (P < 0.001). The relatively low sensitivities and specificities of these serologic tests make them poor tools for the diagnosis of PTB among patients with suspected PTB. However, the relatively high prevalence of positive EIA-IgA results among healthy close contacts of PTB patients warrants further evaluation of this test with close contacts and other populations at risk for recent M. tuberculosis exposure and development of disease.