ESAT-6 and CFP-10: what is the diagnosis?

Decoding the hidden realm: Molecular pioneering unravelling osteoarticular tuberculosis diagnosis

Osteoarticular tuberculosis (TB), a form of extrapulmonary tuberculosis, refers to the involvement of Mycobacterium tuberculosis (M.tb) in the bones and joints. While pulmonary tuberculosis is the most common form, osteoarticular TB represents a relatively rare but significant manifestation, accounting for approximately 1-3% of all TB cases. Accurate and timely diagnosis plays a pivotal role in the management of osteoarticular TB. Conventional diagnostic methods for osteoarticular TB, such as acid-fast bacilli smear microscopy and culture, have limitations in terms of sensitivity, specificity, and turnaround time. The purpose of this review is to comprehensively evaluate and synthesize the existing literature on molecular pioneering in osteoarticular TB diagnosis. Molecular techniques, such as nucleic acid amplification tests and gene-based assays, have emerged as promising tools for diagnosing TB. These techniques target specific genetic sequences of M.tb, enabling rapid and sensitive detection of the pathogen. However, the diagnostic accuracy, advantages, and limitations of these molecular techniques in the context of osteoarticular TB diagnosis require further investigation and consolidation of evidence. Furthermore, this review aims to identify areas for future research and development in the field of molecular diagnostics for osteoarticular TB.

Identification and Characterisation of Nontuberculous Mycobacteria in African Buffaloes (Syncerus caffer), South Africa

Diagnosis of bovine tuberculosis (bTB) may be confounded by immunological cross-reactivity to Mycobacterium bovis antigens when animals are sensitised by certain nontuberculous mycobacteria (NTMs). Therefore, this study aimed to investigate NTM species diversity in African buffalo (Syncerus caffer) respiratory secretions and tissue samples, using a combination of novel molecular tools. Oronasal swabs were collected opportunistically from 120 immobilised buffaloes in historically bTB-free herds. In addition, bronchoalveolar lavage fluid (BALF; n = 10) and tissue samples (n = 19) were obtained during post-mortem examination. Mycobacterial species were identified directly from oronasal swab samples using the Xpert MTB/RIF Ultra qPCR (14/120 positive) and GenoType CMdirect (104/120 positive). In addition, all samples underwent mycobacterial culture, and PCRs targeting hsp65 and rpoB were performed. Overall, 55 NTM species were identified in 36 mycobacterial culture-positive swab samples with presence of esat-6 or cfp-10 detected in 20 of 36 isolates. The predominant species were M. avium complex and M. komanii. Nontuberculous mycobacteria were also isolated from 6 of 10 culture-positive BALF and 4 of 19 culture-positive tissue samples. Our findings demonstrate that there is a high diversity of NTMs present in buffaloes, and further investigation should determine their role in confounding bTB diagnosis in this species.

Modeling Tubercular ESX-1 Secretion Using Mycobacterium marinum

Pathogenic mycobacteria cause chronic and acute diseases ranging from human tuberculosis (TB) to nontubercular infections. Mycobacterium tuberculosis causes both acute and chronic human tuberculosis. Environmentally acquired nontubercular mycobacteria (NTM) cause chronic disease in humans and animals. Not surprisingly, NTM and M. tuberculosis often use shared molecular mechanisms to survive within the host. The ESX-1 system is a specialized secretion system that is essential for virulence and is functionally conserved between M. tuberculosis and Mycobacterium marinum .

Combination of mean spot sizes of ESAT-6 spot-forming cells and modified tuberculosis-specific antigen/phytohemagglutinin ratio of T-SPOT.TB assay in distinguishing between active tuberculosis and latent tuberculosis infection

OBJECTIVES

Distinguishing between active tuberculosis (ATB) and latent tuberculosis infection (LTBI) remains challenging.

METHODS

The modified T-SPOT.TB assay was performed in 499 participants (243 ATB and 256 LTBI) and another 322 participants (162 ATB and 160 LTBI) who were diagnosed in Qiaokou (training) and Caidian (validation) cohort respectively.

RESULTS

The mean spot sizes (MSS) of early secreted antigenic target 6 (ESAT-6) spot-forming cells (SFC) of T-SPOT.TB assay in ATB patients was significantly higher than that in LTBI individuals. 1.0 × 10⁵ was the optimal number of cells added to phytohaemagglutinin (PHA) well for obtaining more accurate TB-specific antigen to phytohaemagglutinin (TBAg/PHA) ratio. The area under the curve of the diagnostic model by combination of ESAT-6 SFC MSS and modified TBAg/PHA ratio in distinguishing ATB from LTBI was 0.959 in training cohort, with a sensitivity of 90.12% and a specificity of 91.02% when a cutoff value of 0.46 was used. This diagnostic model showed similar performance in the validation cohort. The area under the curve, sensitivity, and specificity were 0.962, 93.21%, and 90.00%, respectively. Further flow cytometry analysis showed that ESAT-6 stimulation induced a significantly higher mean fluorescence intensity of IFN-γ⁺ cells in lymphocytes compared with culture filtrate protein 10 (CFP-10) stimulation. In contrast, CFP-10 stimulation induced a significantly higher percentage of IFN-γ⁺ cells in lymphocytes compared with ESAT-6 stimulation.

CONCLUSIONS

The combination of the MSS of ESAT-6 SFC and the modified TBAg/PHA ratio of T-SPOT.TB assay showed great value in discriminating ATB from LTBI.

Trends in Diagnosis for Active Tuberculosis Using Nanomaterials

Background:

Tuberculosis (TB), one of the leading causes of death worldwide, is difficult to diagnose based only on signs and symptoms. Methods for TB detection are continuously being researched to design novel effective clinical tools for the diagnosis of TB.

Objective:

This article reviews the methods to diagnose TB at the latent and active stages and to recognize prospective TB diagnostic methods based on nanomaterials.

Methods:

The current methods for TB diagnosis were reviewed by evaluating their advantages and disadvantages. Furthermore, the trends in TB detection using nanomaterials were discussed regarding their performance capacity for clinical diagnostic applications.

Results:

Current methods such as microscopy, culture, and tuberculin skin test are still being employed to diagnose TB, however, a highly sensitive point of care tool without false results is still needed. The utilization of nanomaterials to detect the specific TB biomarkers with high sensitivity and specificity can provide a possible strategy to rapidly diagnose TB. Although it is challenging for nanodiagnostic platforms to be assessed in clinical trials, active TB diagnosis using nanomaterials is highly expected to achieve clinical significance for regular application. In addition, aspects and future directions in developing the high-efficiency tools to diagnose active TB using advanced nanomaterials are expounded.

Conclusion:

This review suggests that nanomaterials have high potential as rapid, costeffective tools to enhance the diagnostic sensitivity and specificity for the accurate diagnosis, treatment, and prevention of TB. Hence, portable nanobiosensors can be alternative effective tests to be exploited globally after clinical trial execution.

Original Mycobacterial Sin, a consequence of highly homologous antigens?

The role of antigens shared between Mycobacteria in in-vivo cross-reactive immune responses in host animals, have been reported to be responsible for reduced BCG vaccination efficacy as well reduced specificity of routine immunological diagnostic tests. This presents with significant disease control challenges in humans and animals. The present review highlights the results of previous studies on the effect of pre-sensitization to environmental mycobacteria on either pathogenic mycobacteria and/or M. bovis BCG, in experimental animals. It also takes an in-depth view into assessing the genetic similarities and relationships between atypical mycobacteria and Mycobacterium tuberculosis complex (MTBC) and how they might explain the immunological imprint of environmental mycobacteria in directing the hosts' immune response upon subsequent exposure to other classes of mycobacteria. The outcome of this review suggests that genetic closeness between particular atypical mycobacteria and MTBC usually indicate a higher level of homology for certain shared protective antigens. This ultimately results in a higher level of cross reactive immune responses as compared with other atypical mycobacteria that are further away genetically. This would explain the different effects of environmental mycobacteria on MTBC that have been reported in the different studies. In other words the direction of the host immune system in response to exposure to MTBC would depend on the type of environmental mycobacteria that was encountered in the initial exposure. We also explain these mycobacterial interactions in the context of the phenomenon of "Original Mycobacterial Sin". The effects of these inevitable mycobacterial interactions on field diagnosis and control by vaccination and how to circumvent them are discussed.

Immunological Roles of Elevated Plasma Levels of Matricellular Proteins in Japanese Patients with Pulmonary Tuberculosis

Elevated matricellular proteins (MCPs), including osteopontin (OPN) and galectin-9 (Gal-9), were observed in the plasma of patients with Manila-type tuberculosis (TB) previously. Here, we quantified plasma OPN, Gal-9, and soluble CD44 (sCD44) by enzyme-linked immunosorbent assay (ELISA), and another 29 cytokines by Luminex assay in 36 patients with pulmonary TB, six subjects with latent tuberculosis (LTBI), and 19 healthy controls (HCs) from Japan for a better understanding of the roles of MCPs in TB. All TB subjects showed positive results of enzyme-linked immunospot assays (ELISPOTs). Spoligotyping showed that 20 out of 36 Mycobacterium tuberculosis (MTB) strains belong to the Beijing type. The levels of OPN, Gal-9, and sCD44 were higher in TB (positivity of 61.1%, 66.7%, and 63.9%, respectively) than in the HCs. Positive correlations between OPN and Gal-9, between OPN and sCD44, and negative correlation between OPN and ESAT-6-ELISPOT response, between chest X-ray severity score of cavitary TB and ESAT-6-ELISPOT response were observed. Instead of OPN, Gal-9, and sCD44, cytokines G-CSF, GM-CSF, IFN-α, IFN-γ, IL-12p70, and IL-1RA levels were higher in Beijing MTB-infected patients. These findings suggest immunoregulatory, rather than inflammatory, effect of MCPs and can advance the understanding of the roles of MCPs in the context of TB pathology.

Mycobacterium tuberculosis pili (MTP), a putative biomarker for a tuberculosis diagnostic test

Novel biomarkers are urgently needed for point of care TB diagnostics. In this study, we investigated the potential of the pilin subunit protein encoded by the mtp gene as a diagnostic biomarker. BLAST analysis of the mtp gene on published genome databases, and amplicon sequencing were performed in Mycobacterium tuberculosis Complex (MTBC) strains and other organisms. The protein secondary structure of the amino acid sequences of non-tuberculous Mycobacteria that partially aligned with the mtp sequence was analysed with PredictProtein software. The mtp gene and corresponding amino acid sequence of MTBC were 100% homologous with H37Rv, in contrast to the partial alignment of the non-tuberculous Mycobacteria. The mtp gene was present in all 91 clinical isolates of MTBC. Except for 2 strains with point mutations, the sequence was 100% conserved among the clinical strains. The mtp gene could not be amplified in all non-tuberculous Mycobacteria and respiratory organisms. The predicted MTP protein structure of Mycobacterium avium, Mycobacterium ulcerans and Mycobacterium abscessus differed significantly from that of the M. tuberculosis, which was similar to Mycobacterium marinum. The absence of the mtp gene in non-tuberculous Mycobacteria and other respiratory bacteria suggests that its encoded product, the pilin subunit protein of M. tuberculosis may be a suitable marker for a point of care TB test.

Determining the Latent Tuberculosis Infection by IFN - γ Elispot Assay in Healthcare Workers From University Hospitals of Shiraz, South West of Iran

Background

Classical screening methods are incapable to properly detect LTBI (Latent TB Infection) and HCWs (Healthcare Workers) are at the high risk of exposure. Only few reports estimated the prevalence of LTBI among Iranian HCWs and they mostly used the TST (Tuberculin Skin Test), rather than assessing the response against TB-specific antigens.

Objectives

The current study aimed to determine the frequency of IFN - γ producing blood cells of microbiology and radiology ward technicians by an in-house IFN - γ ELISPOT assay in the University hospitals of Shiraz University of Medical Sciences (SUMS) against recombinant ESAT - 6 and PPD antigens.

Materials and Methods

89 HCWs from medical laboratory and radiology departments of Shiraz University of Medical Sciences’ hospitals, South of Iran, were screened for LTBI. To achieve the goal, an in-house IFN - γ (Interferon - gamma) ELISPOT (Enzyme Linked ImmunoSpot) assay was used to detect the reactivity against ESAT - 6 (Early Secreted Antigen Target protein - 6) and the PPD (Purified Protein Derivate).

Results

Almost 8% of the personnel showed positive TST (over 10 mm) reaction while 29% of them had considerable T - cell reactivity against PPD in ELISPOT assays. However, the ESAT - 6 reactivity was found only in one case of HCWs. No correlation was found between the patterns of the reactions and the age or the duration of the employment or previous vaccination history of the participants. The ELISPOT results were not correlated with the TST results.

Conclusions

Considering the hindrance of TST, the IFN - γ ESAT - 6 ELISPOT assay, even in forms of in-house tests, could replace traditional methods to properly spot the LTBI among the high risk groups from Iran’s health system.

Mycobacterium tuberculosis-driven targeted recalibration of macrophage lipid homeostasis promotes the foamy phenotype

Upon infection, Mycobacterium tuberculosis (Mtb) metabolically alters the macrophage to create a niche that is ideally suited to its persistent lifestyle. Infected macrophages acquire a "foamy" phenotype characterized by the accumulation of lipid bodies (LBs), which serve as both a source of nutrients and a secure niche for the bacterium. While the functional significance of the foamy phenotype is appreciated, the biochemical pathways mediating this process are understudied. We found that Mtb induces the foamy phenotype via targeted manipulation of host cellular metabolism to divert the glycolytic pathway toward ketone body synthesis. This dysregulation enabled feedback activation of the anti-lipolytic G protein-coupled receptor GPR109A, leading to perturbations in lipid homeostasis and consequent accumulation of LBs in the macrophage. ESAT-6, a secreted Mtb virulence factor, mediates the enforcement of this feedback loop. Finally, we demonstrate that pharmacological targeting of pathways mediating this host-pathogen metabolic crosstalk provides a potential strategy for developing tuberculosis chemotherapy.

Modification of the QuantiFERON-TB Gold (In-Tube) assay for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

African buffaloes (Syncerus caffer) are the most significant wildlife maintenance hosts of Mycobacterium bovis, the causative organism of bovine tuberculosis (BTB). Current diagnostic tests for the detection of M. bovis infection in free-ranging buffaloes have numerous limitations and we wished to evaluate a modification to a human TB assay, the QuantiFERON-TB Gold (In-Tube) assay (QFT), as a practical diagnostic test for BTB in buffaloes. One hundred and seventy-five buffaloes were tested using the single intradermal comparative tuberculin test (SICTT) and a modified QFT (mQFT). An appropriate cut-off point for the mQFT was derived from SICTT results using receiver operator characteristic curve analysis. Twenty-six SICTT-positive buffaloes were killed and subjected to necropsy, and selected tissues were processed for mycobacterial culture and speciation. An optimal cut-off point for the mQFT was calculated as 66pg/ml. The assay correctly detected 39/40 SICTT-positive buffaloes and 129/134 TST-negative buffaloes and M. bovis was cultured from 21/26 slaughtered SICTT/mQFT-positive animals. The mQFT shows promise as a practical test for M. bovis infection in buffaloes and shows a sensitivity and specificity at least similar to that of the TST.

IFN-gamma-release assays in the management of tuberculosis

New blood tests for TB are now available. One measures the release of IFN-gamma and the other estimates the number of cells secreting IFN-gamma after stimulation with antigens from Mycobacterium tuberculosis. The choice of antigens (esat-6 and cfp-10) is intended to distinguish TB infection from Bacille Calmette-Guerin vaccination. Tests differ in lymphocyte numbers, the use of an additional antigen (TB7.7 - Rv2654) and sensitivity in concurrent HIV infection. Their role in the routine diagnosis of TB is limited. In latent TB infection, the new tests correlate better with exposure to TB. However, the time course of the immune response, the significance of negative tests, conversions from positive to negative and vice versa and their value in predicting who will develop TB are not yet known. Prospective studies of these tests are needed to establish their practical value rather than theoretical role in latent TB infection. Cohorts of both immunocompetent and immunosuppressed subjects who may develop active disease should be examined.

Diagnostic value of early secreted antigenic target-6 for the diagnosis of tuberculous meningitis patients

BACKGROUND

The early diagnosis of tuberculous meningitis (TBM) is very crucial, since delayed diagnosis can lead to various neurological manifestations. We have previously developed an in-house indirect enzyme-linked immunosorbent assay (ELISA) for TBM diagnosis using the Antigen 85 (Ag 85) complex. It has been suggested that the Ag 85 complex might give false-positive reactions for individuals vaccinated with Bacillus Calmette-Guérin (BCG).

OBJECTIVES

In the present study, we describe a prospective evaluation demonstrating that early secreted antigenic target- 6 (ESAT-6), which is absent in Mycobacterium bovis BCG strains, is in the cerebrospinal fluid (CSF) of TBM patients.

METHODS

We used an indirect ELISA to detect ESAT-6 antigens in the CSF of TBM patients using polyclonal antibodies against ESAT-6.

RESULTS

Using the indirect ELISA method, we demonstrated a sensitivity and specificity of 80% and 94%, respectively, for the diagnosis of TBM.

CONCLUSION

The detection of ESAT-6 in the CSF of TBM patients by indirect ELISA is a promising method and can be used to develop an immunodiagnostic assay with increased sensitivity and specificity.

Protein secretion systems in Mycobacteria

Mycobacteria have a unique cell-envelope structure which protects the bacteria from the extracellular environment by limiting access to noxious molecules from the outside. This extremely hydrophobic and thick barrier also poses a unique problem for the export of bacterial products. Here we review the multiple protein secretion pathways in Mycobacteria, including the general secretion pathway and the Twin-Arginine Transporter, with an emphasis on the ESX-1 alternate secretion system. This newly identified protein secretion system is required for growth during infection and has provided insight into how M. tuberculosis manipulates the host immune response during infection.

Advances in bovine tuberculosis diagnosis and pathogenesis: What policy makers need to know

The mainstay of tuberculosis diagnosis in cattle and deer has been the tuberculin skin test. Recent advances have allowed the incorporation of blood based assays to the diagnostic arsenal for both cattle and deer. Use of defined and specific antigens has allowed for improved specificity of cell mediated assays in both cattle and deer and advances in antibody tests for tuberculosis have potential for use in free-ranging and captive cervid populations. Combined use of blood-based assays with skin testing will require further understanding of the effect of skin testing on the accuracy of blood based assays. Models of experimental infection of cattle have allowed for increased understanding of natural disease pathogenesis. Differences likely exist; however, between cattle and deer in both disease distribution and primary route of inoculation in naturally infected animals.

Utility of the antigen-specific interferon-gamma assay for the management of tuberculosis

PURPOSE OF REVIEW

The tuberculin skin test, now over a century old, is prone to reader variability, and outcomes are influenced by cross-reactivity with environmental mycobacteria, previous bacillus Calmette-Guerin (BCG) vaccination, and anergy in immunosuppressed individuals. More recently, T-cell-based interferon-gamma responses to Mycobacterium tuberculosis - specific antigens have been investigated for their role in diagnosing latent tuberculosis infection.

RECENT FINDINGS

We review the evidence supporting the utility of the interferon-gamma assay for the diagnosis of latent tuberculosis infection (LTBI) in low-prevalence countries. We discuss the principle of the test, technical factors related to performance, and its utility in active tuberculosis, in specialised subgroups such as immunocompromised patients, and its applicability in developing countries.

SUMMARY

Compared with the tuberculin skin test, the antigen-specific interferon-gamma assay, when used in a standardised protocol (overnight incubation assay using a combination of two antigens) for the diagnosis of LTBI, has greater specificity in BCG-vaccinated individuals, displays a stronger association with exposure, and is less biased by environmental mycobacteria such as Mycobacterium avium. Prospective studies are required, however, to confirm that treating LTBI, as defined by the interferon-gamma assay, will reduce the tuberculosis burden in low-prevalence countries and whether interferon-gamma responses are predictive of those who have a high risk of progression to active tuberculosis. Further studies are required to address the utility of the interferon-gamma assay in specialised subgroups of patients, in developing countries, and as a marker of disease activity.

Large-scale evaluation of enzyme-linked immunospot assay and skin test for diagnosis of Mycobacterium tuberculosis infection against a gradient of exposure in The Gambia

The purified protein derivative (PPD) skin test for Mycobacterium tuberculosis infection lacks specificity. We assessed 2 more specific M. tuberculosis antigens (ESAT-6 and CFP-10) by enzyme-linked immunospot assay (ELISPOT) compared with PPD by ELISPOT and skin test in The Gambia. Of 735 household contacts of 130 sputum smear-positive tuberculosis cases, 476 (65%) tested positive by PPD ELISPOT, 300 (41%) tested positive by PPD skin test, and 218 (30%) tested positive by ESAT-6/CFP-10 ELISPOT. Only 15 (2%) had positive ESAT-6/CFP-10 results and negative PPD results by ELISPOT. With increasing M. tuberculosis exposure, the percentage of subjects who were PPD skin test positive/ESAT-6/CFP-10 ELISPOT negative increased (P<.001), whereas the percentage of subjects who were PPD skin test negative/PPD ELISPOT positive decreased (P=.011). Eighteen (31%) ESAT-6/CFP-10 ELISPOT-positive subjects in the lowest exposure category had negative PPD skin test results. ESAT-6/CFP-10 ELISPOT probably offers increased specificity in the diagnosis of M. tuberculosis infection in this tropical setting of endemicity, at the cost of some sensitivity.