Diagnostic Accuracy of the Abbott SD Bioline MPT64 antigen test for identification of MTB Complex in a U.S. Clinical Mycobacteriology Laboratory

Identification of the Mycobacterium tuberculosis complex (MTBC) from culture and differentiation from other non-tuberculous mycobacterial species is required for rapid diagnosis and accurate treatment. However, gaps exist in culture-based identification of acid-fast bacilli (AFB) positive cultures for rapid rule-out of MTBC in the United States. The SD Bioline™ MPT64 (Abbott Inc, South Korea) lateral flow assay (LFA) has high sensitivity and specificity for the detection of MTBC in liquid culture but has not been evaluated in a clinical mycobacteriology laboratory in the United States. We conducted a diagnostic accuracy study of this LFA for detection of MTBC versus NTMs on AFB positive cultures. A total of 362 tests were performed, with a sensitivity and specificity of 100 % (362/362) across all tests. The SD Bioline MPT64 assay provides accurate test results with AFB-positive liquid cultures and could fill the current gap for rapid rule-out of MTBC in U.S.-based clinical laboratories.

Ultrasensitive biosensing platform for Mycobacterium tuberculosis detection based on functionalized graphene devices

Tuberculosis (TB) has high morbidity as a chronic infectious disease transmitted mainly through the respiratory tract. However, the conventional diagnosis methods for TB are time-consuming and require specialists, making the diagnosis of TB with point-of-care (POC) detection difficult. Here, we developed a graphene-based field-effect transistor (GFET) biosensor for detecting the MPT64 protein of Mycobacterium tuberculosis with high sensitivity as a POC detection platform for TB. For effective conjugation of antibodies, the graphene channels of the GFET were functionalized by immobilizing 1,5-diaminonaphthalene (1,5-DAN) and glutaraldehyde linker molecules onto the graphene surface. The successful immobilization of linker molecules with spatial uniformity on the graphene surface and subsequent antibody conjugation were confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. The GFET functionalized with MPT64 antibodies showed MPT64 detection with a detection limit of 1 fg/mL in real-time, indicating that the GFET biosensor is highly sensitive. Compared to rapid detection tests (RDT) and enzyme-linked immunosorbent assays, the GFET biosensor platform developed in this study showed much higher sensitivity but much smaller dynamic range. Due to its high sensitivity, the GFET biosensor platform can bridge the gap between time-consuming molecular diagnostics and low-sensitivity RDT, potentially aiding in early detection or management of relapses in infectious diseases.

Rapid diagnosis of TB using Aptamer-based assays for Mycobacterium tuberculosis antigens in children and adolescents

Background

Despite advances establishing microbiological evidence of tuberculosis (TB) is still a concern in children due to the limitation of availability of sample and predominance of extrapulmonary TB, there is unmet need for diagnostic tests which are low cost, rapid and sensitive and specific.

Methods

This study evaluated the utility of aptamer-based assay for detecting mycobacterium tuberculosis antigens HspX and MPT 64 in rapid diagnosis of TB in children up to 18 years of age in a tertiary medical college. A total of 100 children were sequentially enrolled with presumptive pulmonary (n = 52 and extrapulmonary n = 48) TB based on clinico-radiological characteristics. The samples were evaluated with ALISA technique for TB antigens and compared with the results of ZN microscopy, GeneXpert and mycobacterial culture MGIT.

Results

The enrolled children had mean age (11.7 + 4.4 years) with both pulmonary (n = 52) and extrapulmonary TB (n = 48). Our study results concluded poor results of smears (11% positivity, sensitivity: 17.7%, NPV: 42.7%) and better of GeneXpert (positivity: 42%, sensitivity of 67.4%, NPV: 65.5%) and culture (positivity 57%, sensitivity 91.9%, NPV 88.3%). HspX antigen by ALISA had comparable results (positivity: 49%, sensitivity: 62.9%; NPV: 54.9%). MPT 64 antigen by ALISA also had similar results (positivity: 45%, sensitivity: 58% and NPV 52, 3%). Sensitivity and specificity were higher in pulmonary TB compared to EPTB for both antigens. HspX antigen assay by ALISA and MPT 64 ALISA over existing microbiological diagnostic methods had additional of 13%.

Conclusion

ALISA technique for mycobacterium antigens HspX and MPT 64 was rapid, low-cost test (1-3$/test) high sensitivity and specificity and comparable to currently available methods.

Gel Protein Extraction's Impact on Conformational Epitopes of Linear Non-Tagged MPT64 Protein

The production and purification of recombinant proteins are crucial to acquiring pure MPT64 protein. Due to the fact that protein epitopes may undergo conformational changes during purification, this study, therefore, investigated an effective rapid purification method to produce highly intracellular pure MPT64 protein without causing conformational changes in the epitope under denaturing conditions. MPT64 was isolated from E. coli and electrophoresed using gel SDS-PAGE. Then, the desired protein bands were excised and purified with two methods: electroelution and passive elution. The isolated protein was identified via peptide mass fingerprinting using MALDI-TOF MS and reacted with IgG anti-MPT64, and the cross-reactivity of the isolated protein with IgY anti-MPT64 was confirmed using Western blot. The results show that both of these methods produced pure MPT64 protein, and the MPT64 protein was confirmed based on the MALDI-TOF MS results. Neither of these two methods resulted in epitope changes in the MPT64 protein so it could react specifically with both antibodies. The yield of MPT64 protein was higher with electroelution (2030 ± 41 µg/mL) than with passive elution (179.5 ± 7.5 µg/mL). Thus, it can be inferred that the electroelution method is a more effective method of purifying MPT64 protein and maintaining its epitope than the passive elution method.

MPT51 and MPT64-based antigen detection assay for the diagnosis of extrapulmonary tuberculosis from urine samples

In view of WHO's "End-TB" strategy, we developed a non-invasive, urine-based ELISA, targeting 2 Mycobacterium tuberculosis antigens namely MPT51 and MPT64 for extrapulmonary TB (EPTB) diagnosis. Suspected EPTB patients (n = 137) [Pleural TB, Abdominal TB and Tuberculous meningitis] were categorized in "Definite" EPTB (n = 10) [Xpert-MTB/RIF and/or culture-positive], "Probable" EPTB (n = 77) and "Non-EPTB" (n = 50) groups using defined composite reference standards. ROC-curves were generated using ELISA results of "Definite" EPTB and "Non-EPTB" groups for both antigens independently and cut-off values were selected to provide 86.3% (95%CI:73.3-94.2) specificity for MPT51 and 92% (95%CI:80.8-97.8) for MPT64. The sensitivity of MPT51-ELISA and MPT64-ELISA was 70% (95%CI:34.7-93.3) and 90% (95%CI:55.5-99.7) for "Definite" EPTB group and 32.5% (95%CI:22.2-44.1) and 30.8% (95%CI:20.8-42.2) for "Probable" EPTB group, respectively. Combining the results of both ELISAs showed a 100% (95%CI:69.1-100) sensitivity in "Definite" EPTB group and 41.6% (95%CI:30.4-53.4) in "Probable" EPTB group, with an 80% (95%CI:66.3-89.9) specificity. The results demonstrated the potential of urine-based ELISAs as screening tests for EPTB diagnosis.

Novel Mutations in MPT64 Secretory Protein of Mycobacterium tuberculosis Complex

Tuberculosis (TB) is a global health problem caused by the Mycobacterium tuberculosis complex (MTBC). These bacteria secrete various proteins involved in the pathogenesis and persistence of MTBC. Among the secretory proteins, MPT64 (Rv1980C) is highly conserved and is also known as a major culture filtrate that is used in rapid diagnosis of MTBC. In the current study, we aimed to find the mutation in this highly conserved protein in isolates from the Pashtun-dominant province of Pakistan. We analyzed 470 M. tuberculosis whole-genome sequences of Khyber Pakhtunkhwa Province. Mutations in the MPT64 gene were screened through TB-Profiler and BioEdit software tools. The DynaMut web server was used to analyze the impact of the mutation on protein dynamics and stability. Among 470 MTB genomes, three non-synonymous mutations were detected in nine isolates, and one synonymous mutation (G208A) was found in four isolates. Mutation G211T (F159L), which was detected at the C-terminal domain of the protein in six isolates, was the most prominent. The second novel mutation, T480C (I70V), was detected in two isolates at the C-terminal side of the protein structure. The third novel mutation, A491C (L66R), was detected in a single isolate at the N-terminal side of the MPT64 protein. The effect of these three mutations was destabilizing on the protein structure. The molecular flexibility of the first two mutations increased, and the last one decreased. MPT64 is a highly conserved secretory protein, harboring only a few mutations. This study provides useful information for better managing the diagnosis of MTB isolates in high TB-burden countries.

Non-amplification nucleic acid detection with thio-NAD cycling

The PCR technique is indispensable in biology and medicine, but some difficulties are associated with its use, including false positive or false negative amplifications. To avoid these issues, a non-amplification nucleic acid detection protocol is needed. In the present study, we propose a method in which nucleic-acid probe hybridization is combined with thio-NAD cycling to detect nucleic acids without amplification. We report our application of this method for the detection of the gene of MPT64 in Mycobacterium tuberculosis. Two different cDNA probes targeted the mpt64 gene: the first probe was used to immobilize the mpt64 gene, and the second probe, linked with alkaline phosphatase (ALP), was hybridized to a target sequence in the mpt64 gene. A substrate was then hydrolyzed by ALP, and a cycling reaction was conducted by a dehydrogenase with its co-factors (thio-NAD and NADH). The single-stranded DNA, double-stranded DNA, plasmid DNA for the mpt64 gene, and whole genome of M. tuberculosis var. BCG were detected at the level of 10⁵-10⁶ copies/assay, whereas the non-tuberculosis mycobacteria (e.g., M. avium, M. intracellulare, M. kansasii, and M. abscessus) were below the limits of detection. The present method enables us to avoid the errors inherent in nucleic acid amplification methods.

Simultaneous Amperometric Aptasensor Based on Diazonium Grafted Screen-Printed Carbon Electrode for Detection of CFP10 and MPT64 Biomarkers for Early Tuberculosis Diagnosis

Early diagnosis is highly crucial for life-saving and transmission management of tuberculosis (TB). Despite the low sensitivity and time-consuming issues, TB antigen detection still relies on conventional smear microscopy and culture techniques. To address this limitation, we report the development of the first amperometric dual aptasensor for the simultaneous detection of Mycobacterium tuberculosis secreted antigens CFP10 and MPT64 for better diagnosis and control of TB. The developed sensor was based on the aptamers-antibodies sandwich assay and detected by chronoamperometry through the electrocatalytic reaction between peroxidase-conjugated antibodies, H₂O₂, and hydroquinone. The CFP10 and MPT64 aptamers were immobilized via carbodiimide covalent chemistry over the disposable dual screen-printed carbon electrodes modified with a 4-carboxyphenyl diazonium salt. Under optimized conditions, the aptasensor achieved a detection limit of 1.68 ng mL^-1 and 1.82 ng mL^-1 for CFP10 and MPT64 antigens, respectively. The developed assay requires a small sample amount (5 µL) and can be easily performed within 2.5 h. Finally, the dual aptasensor was successfully applied to clinical sputum samples with the obtained diagnostic sensitivity (n = 24) and specificity (n = 13) of 100%, respectively, suggesting the readiness of the developed assay to be used for TB clinical application.

Improving of pelB-Secreted MPT64 protein released by Escherichia coli BL21 (DE3) using Triton X-100 and Tween-80

pelB has been known as a successful signal peptide to translocate the protein target extracellularly in the Escherichia coli system. However, in our previous study, the yield of MPT64 protein extracellular recovery was still low and plenty of this protein was remain trapped in cytoplasm and periplasm. Recently, nonionic surfactants were efficiently reported to secrete recombinant protein extracellularly. Nonetheless, it must be clarified whether the surfactant supplementation can improve the yield of MPT64 extracellular protein significantly without giving impact on the structure of isolated MPT64 protein and can minimized the cell lysis effect. MPT64 protein secretion was carried out by comparing the effects of surfactants Tween 80 and Triton × 100 at various concentrations. Triton × 100 was able to increase the extracellular MPT64 protein gain up to 3 times higher than Tween 80 and it was in line with the greater level ratio of cell leakage of Triton × 100 compared to that of Tween 80. Similarly, the viable cell of the cultures decreased dramatically. However, both surfactants did not interfere the structure of MPT64 protein. In conclusion, Triton × 100 can be chosen as the supporting surfactant to assist the act of peptide signal in improving the resulting of MPT64 extracellular protein.

Performance assessment of SD Bioline TB MPT64 assay for the diagnosis of Mycobacterium tuberculosis complex in Lagos, Nigeria

This study assessed the performance of SD Bioline MPT64 immunochromatographic test for the identification of Mycobacterium tuberculosis complex (MTBC) in Nigeria.A total of 157 mycobacterial isolates, comprising 120 (76.4%) MTBC (M. tuberculosis, 112; M. africanum, 5; M. bovis, 3) and 37 (23.6%) non-tuberculous mycobacteria (NTM) isolates from patients attending six DOTS centers in Lagos between June 2012 and July 2014 were analyzed. All the isolates were grown on Bactec MGIT960 liquid media and identified in parallel by the conventional method and MPT64 immunochromatographic test. Discrepant results were resolved using the line probe assay.The comorbid disease rates for HIV and type 2 diabetes were 20.9% and 8.2%, respectively. Compared to the conventional method, SD Bioline MPT64 identified 117 MTBC isolates correctly, producing a sensitivity of 97.5% (95% CI, 92.9-99.2) at a shorter growing median time of 11 days compared to 26 days by the conventional method. The three undetected MTBC were confirmed by the line probe assay to be M. tuberculosis strains. The test also identified all the NTM correctly producing a specificity of 100% (95% CI, 90.7-100).This study supports the integration of SD Bioline TB MPT64 antigen test into diagnostic workflow for rapid MTBC case identification in Nigeria.

Immunochemistry-Based Diagnosis of Extrapulmonary Tuberculosis: A Strategy for Large-Scale Production of MPT64-Antibodies for Use in the MPT64 Antigen Detection Test

Tuberculosis (TB) is a global health problem. The immunohistochemistry (IHC)-based MPT64 antigen detection test has shown promising results for diagnosing extrapulmonary TB in previous studies. However, the anti-MPT64 antibody currently used in the test is in limited supply, and reproduction of a functional antibody is a prerequisite for further large-scale use. Various antigen-adjuvant combinations and immunisation protocols were tested in mice and rabbits to generate monoclonal and polyclonal antibodies. Antibodies were screened in IHC, and the final new antibody was validated on clinical human specimens. We were not able to generate monoclonal antibodies that were functional in IHC, but we obtained multiple functional polyclonal antibodies through careful selection of antigen-adjuvant and comprehensive screening in IHC of both pre-immune sera and antisera. To overcome the limitation of batch-to-batch variability with polyclonal antibodies, the best performing individual polyclonal antibodies were pooled to one final large-volume new anti-MPT64 antibody. The sensitivity of the new antibody was in the same range as the reference antibody, while the specificity was somewhat reduced. Our results suggest that it possible to reproduce a large-volume functional polyclonal antibody with stable performance, thereby securing stable supplies and reproducibility of the MPT64 test, albeit further validation remains to be done.

MPT64 assays for the rapid detection of Mycobacterium tuberculosis

Background

Tuberculosis (TB) is a serious infectious disease caused by Mycobacterium tuberculosis (MTB). An estimated 1.7 billion people worldwide are infected with Mycobacterium tuberculosis (LTBI) during the incubation period without any obvious symptoms. Because of MTB’s high infection and mortality rates, there is an urgent need to develop a fast, portable, and sensitive diagnostic technology for its detection.

Methods

We included research from PubMed, Cochrane Library, Web of Science, and Embase and extracted the data. MetaDisc and STATA were used to build forest plots, Deek’s funnel plot, Fagan plot, and bivariate boxplot for analysis.

Results

Forty-six articles were analyzed, the results of which are as follows: sensitivity and specificity were 0.92 (0.91–0.93) and 0.95 (0.94–0.95) respectively. The NLR and PLR were 0.04 (95% CI 0.03–0.07) and 25.32 (95% CI 12.38–51.78) respectively. DOR was 639.60 (243.04–1683.18). The area under the SROC curve (AUC) was 0.99.

Conclusions

MPT64 exhibits good diagnostic efficiency for MTB. There is no obvious heterogeneity between the three commercial kits.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06022-w.

Comparison of simple and rapid extracting methods of free-tags Mycobacterium tuberculosis protein 64 Recombinant Protein from polyacrylamide gel: Electroelution and the optimized passive elution

In this study, the Mycobacterium tuberculosis protein 64 (MPT64) protein was constructed without any tags to facilitate the purification using column affinity chromatography, but the MPT64 must be obtained as a pure protein. This study was purpose to ensure the efficient extracting method to purify protein MPT64 directly from the polyacrylamide gel. The crude extract of extracellular protein containing MPT64 protein was separated into single protein band and the targeted protein which is located in the size of 24 kDa was excised. Each of the six bands was collected in a sterile microtube to be eluted using electroelution and the optimized of the passive-elution method. Both the elution methods demonstrated the purity level of the MPT64 protein by detecting a solely band on the gel at the 24 kDa. Among the variety of passive-elution time, the highest MPT64 protein concentration was 0.549 mg/ml after elution for 72 h. However, the electroelution result provided higher MPT64 protein concentration, i.e., 0.683 mg/mL. However, based on the recognition of the purified MPT64 protein on commercial detection kit of MPT64 protein, it showed that the positive result was only showed by the passive-elution extracting protein. Therefore, for purifying the protein MPT64 from the sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, the efficient method was passive elution.

A novel, rapid (within hours) culture-free diagnostic method for detecting live Mycobacterium tuberculosis with high sensitivity

BACKGROUND

Nucleic acid amplification tests (NAATs) are widely used to diagnose tuberculosis (TB), but cannot discriminate live bacilli from dead bacilli. Live bacilli can be isolated by culture methods, but this is time-consuming. We developed a de novo TB diagnostic method that detects only live bacilli with high sensitivity within hours.

METHODS

A prospective study was performed in Taiwan from 2017 to 2018. Sputum was collected consecutively from 1102 patients with suspected TB infection. The sputum was pretreated and heated at 46°C for 1 h to induce the secretion of MPT64 protein from live Mycobacterium tuberculosis. MPT64 was detected with our ultrasensitive enzyme-linked immunosorbent assay (ELISA) coupled with thionicotinamide-adenine dinucleotide (thio-NAD) cycling. We compared our data with those obtained using a culture test (MGIT), a smear test (Kinyoun staining), and a NAAT (Xpert).

FINDINGS

The limit of detection for MPT64 in our culture-free ultrasensitive ELISA was 2.0 × 10-19 moles/assay. When the criterion for a positive response was set as an absorbance value ≥17 mAbs, this value corresponded to ca. 330 CFU/mL in the culture method - almost the same high-detection sensitivity as the culture method. To confirm that MPT64 is secreted from only live bacilli, M. bovis BCG was killed using 8 μg/mL rifampicin and then heated. Following this procedure, our method detected no MPT64. Our rapid ultra-sensitive ELISA-based method required only 5 h to complete. Comparing the results of our method with those of culture tests for 944 specimens revealed a sensitivity of 86.9% (93/107, 95% CI: 79.0-92.7%) and a specificity of 92.0% (770/837, 95% CI: 89.9-93.7%). The performance data were not significantly different (McNemar's test, P = 0.887) from those of the Xpert tests. In addition, at a ≥1+ titer in the smear test, the positive predictive value of our culture-free ultrasensitive ELISA tests was in a good agreement with that of the culture tests. Furthermore, our culture-free ultrasensitive ELISA test had better validity for drug effectiveness examination than Xpert tests because our test detected only live bacilli.

INTERPRETATION

Our culture-free ultrasensitive ELISA method detects only live TB bacilli with high sensitivity within hours, allowing for rapid diagnosis of TB and monitoring drug efficacy.

FUNDING

Matching Planner Program from JST (VP29117939087), the A-STEP Program from JST (AS3015096U), Waseda University grants for Specific Research Projects (2017A-015 and 2019C-123), the Precise Measurement Technology Promotion Foundation to E.I.

Mycobacterial antigens in pleural fluid mononuclear cells to diagnose pleural tuberculosis in HIV co-infected patients

Background

Extra pulmonary manifestation of tuberculosis (TB) accounts for approximately one-half of TB cases in HIV-infected individuals with pleural TB as the second most common location. Even though mycobacteria are cleared, mycobacterial antigens may persist in infected tissues, causing sustained inflammation and chronicity of the disease. The aim of this study was to explore various mycobacterial antigens in pleural effusions, the impact of HIV infection and CD4+ T-cell depletion on the presence of antigens, and the diagnostic potential of antigens for improved and rapid diagnosis of pleural TB.

Methods

Pleural fluid specimens were collected from patients presenting with clinically suspected pleural TB, and processed routinely for culture, cytology, and adenosine deaminase activity analysis. HIV status and CD4+ T-cell counts were recorded. Pleural fluid mononuclear cells (PFMC) were isolated, and cell smears were stained with acid-fast staining and immunocytochemistry for various mycobacterial antigens. Real-time and nested-PCR were performed. Patients were categorized as pleural TB or non-TB cases using a composite reference standard. Performance of the mycobacterial antigens as diagnostic test was assessed.

Results

A total of 41 patients were enrolled, of which 32 were classified as pleural TB and 9 as non-TB. Thirteen patients had culture confirmed pleural TB, 26 (81%) were HIV-TB co-infected, and 64% had < 100 CD4+ T-cells/microL. Both secreted and cell-wall mycobacterial antigens were detected in PFMC. Lipoarabinomannan (LAM) was the most frequently detected antigen. There was no direct correlation between positive culture and antigens. Cases with low CD4+ T-cell counts had higher bacterial and antigen burden. By combining detection of secreted antigen or LAM, the sensitivity and specificity to diagnose pleural TB was 56 and 78%, respectively, as compared to 41 and 100% for culture, 53 and 89% for nested PCR, and 6 and 100% for real-time PCR.

Conclusion

Mycobacterial antigens were detectable in PFMC from tuberculous pleural effusions, even in cases where viable mycobacteria or bacterial DNA were not always detected. Thus, a combination of secreted antigen and LAM detection by immunocytochemistry may be a complement to acid-fast staining and contribute to rapid and accurate diagnosis of pleural TB.

Ultrasensitive enzyme-linked immunosorbent assay for the detection of MPT64 secretory antigen to evaluate Mycobacterium tuberculosis viability in sputum

OBJECTIVES

This study examined Mycobacterium tuberculosis (MTB)-secreted MPT64 as a surrogate of bacterial viability for the diagnosis of active pulmonary TB (PTB) and for follow-up treatment.

METHODS

In this proof-of-concept prospective study, 50 PTB patients in the Tokyo metropolitan region, between 2017 and 2018, were consecutively included and 30 healthy individuals were also included. Each PTB patient submitted sputum on days 0, 14 and 28 for diagnosis and follow-up, and each healthy individual submitted one sputum sample. The following were performed: smear microscopy, Xpert MTB/RIF, MGIT and solid culture, and MPT64 detection on the sputum samples. Ultrasensitive ELISA (usELISA) was used to detect MPT64. The receiver operating characteristic analyses for diagnosis and follow-up revealed the optimal cut-off value of MPT64 absorbance for detecting culture positivity at multiple intervals.

RESULTS

The sensitivity of MPT64 for diagnosing PTB was 88.0% (95% CI 75.7-95.5) and the specificity was 96.7% (95% CI 82.8-99.9). The specificity of MPT64 for predicting negative culture results on day 14 was 89.5% (95% CI 66.9-98.7). The sensitivity of MPT64 for predicting positive culture results on day 28 was 81.0% (95% CI 58.1-94.6).

CONCLUSIONS

This study revealed that MPT64 is useful for diagnosing active PTB in patients and predicting treatment efficacy at follow-up.

Real-time monitoring of rhamnose induction effect on the expression of mpt64 gene fused with pelB signal peptide in Escherichia coli BL21 (DE3)

In this research, Escherichia coli BL21 (DE3) harboring an expression vector constructed with a rhamnose-inducible promoter and a pelB signal peptide was used as a host cell to produce MPT64 protein. The objective of this research was to figure out the optimum time of mpt64 gene expression through real-time monitoring of MPT64 protein production and distribution in host compartments. The mpt64 expression was regulated by the rhamnose presence at a concentration of 4 mM. The real-time isolated protein was monitored using polyacrylamide gel electrophoresis in denaturation condition. Based on real-time monitoring, the MPT64 protein (24 kDa) in the cytoplasm was optimum detected at 24 h after induction. For periplasmic fraction, the protein was detected at 4 h after induction but thinning at 15 h after induction. At 16 h after induction, the MPT64 protein band was found in the medium with increasing concentrations until 24 h. Thus, it can be concluded that the mpt64 gene expression was regulated in the presence of rhamnose as an inducer, and the proteins were shown to be translocated throughout the host cell compartment with different levels of protein accumulation at different times, according to the role of pelB as a signal peptide.

Diagnosis of extrapulmonary tuberculosis using the MPT64 antigen detection test in a high-income low tuberculosis prevalence setting

BACKGROUND

Extrapulmonary tuberculosis (EPTB) poses diagnostic challenges due to the paucibacillary nature of the disease. The immunochemistry-based MPT64 antigen detection test (MPT64 test) has shown promising results for diagnosing EPTB in previous studies performed in low-resource settings, with higher sensitivity than microscopy and culture. The aim of this study was to investigate the performance of the MPT64 test in a routine clinical setting in a high-income low TB prevalence country.

METHODS

Extrapulmonary samples sent for TB diagnostics to microbiology and pathology laboratories at three regional tertiary care hospitals in Norway in a one-year period were included and subjected to the MPT64 test in parallel to the routine TB diagnostic tests.

RESULTS

Samples from 288 patients were included and categorised as confirmed TB cases (n = 26), clinically diagnosed TB cases (n = 5), non-TB cases (n = 243) and uncategorised (n = 14), using a composite reference standard (CRS). In formalin-fixed biopsies, the sensitivity (95% CI) of the MPT64 test, microscopy, PCR-based tests pooled, and culture was 37% (16-62), 20% (4-48), 37% (16-62) and 50% (23-77), respectively, against the CRS. The MPT64 test showed a good positive predictive value (88%) and an excellent specificity (99, 95% CI 92-100) in formalin-fixed biopsies. In fine-needle aspirates, pus and fluid samples, the test performance was lower.

CONCLUSIONS

The MPT64 test was implementable in pathology laboratories as part of routine diagnostics, and although the sensitivity of the MPT64 test was not better than culture in this setting, the test supplements other rapid diagnostic methods, including microscopy and PCR-based tests, and can contribute to strengthen the diagnosis of EPTB in formalin-fixed biopsies in the absence of culture confirmation.

Mutation in MPT64 gene influencing diagnostic accuracy of SD Bioline assay (capilia)

Background

Success of India’s TB control program relies on rapid case detection, monitoring, care and treatment of drug resistance. Patients on multidrug resistance (MDR) treatment are monitored by follow up cultures. Discordant results (culture and smear positive while capilia negative) are usually declared negative Mycobacterium tuberculosis complex (MTBC). This study was designed to understand the possible causes of discordant results.

Methods

The capilia kit was evaluated to test its utility among 4737 follow up MDR patients enrolled during a period of 1 year. A total of 889 were liquid culture positive, 3375 were negative and 473 were contaminated. Of the 889 cultures positive, 829 were found positive by ZN smear, capilia test and MTBDR plus assay. The cultures which gave a positive result on Mycobacterium Growth Indicator Tube 960 (MGIT 960) and ZN smear but were negative on capilia test with no growth on Brain Heart Infusion agar (BHI) were included in this study. The conflicting results of capilia were compared with other molecular techniques; MTBDR plus assay and DNA sequence analysis of MPT64 gene.

Results

Out of 889 culture positive, 60 (6.7%) were found positive on liquid culture and ZN smear but were negative on capilia. Of these 60 cultures, 10 (16.7%) were found positive by both MTBDR plus assay and PCR. The sequencing analysis revealed that all of the capilia negative isolates had mutations within the MPT64 gene.

Conclusion

Re-evaluation of culture positive but capilia negative isolates should be done before declaring them as Mycobacterium other than tuberculosis (MOTT) because such cases can act as chronic carriers of TB in the population which can lead to the rise of this lethal disease.

Optimization of culture conditions for Mpt64 synthetic gene expression in Escherichia coli BL21 (DE3) using surface response methodology

MPT64 is a specific protein that is secreted by Mycobacterium tuberculosis complex (MTBC). The objective of this study was to obtain optimum culture conditions for MPT64 synthetic gene expression in Escherichia coli BL21 (DE3) by response surface methodology (RSM). The RSM was undertaken to optimize the culture conditions under different cultivation conditions (medium concentration, induction time and inducer concentration), designed by the factorial Box-Bhenken using Minitab 17 statistical software. From the randomized combination, 15 treatments and three center point repetitions were obtained. Furthermore, expression methods were carried out in the flask scale fermentation in accordance with the predetermined design. Then, the MPT64 protein in the cytoplasm of E. coli cell was isolated and characterized using sodium dodecyl sulfate polyacrilamide electrophoresis (SDS-PAGE) then quantified using the ImageJ program. The optimum conditions were two-fold medium concentration (tryptone 20 mg/mL, yeast extract 10 mg/mL, and sodium chloride 20 mg/mL), 5 h of induction time and 4 mM rhamnose. The average concentration of recombinant MPT64 at optimum conditions was 0.0392 mg/mL, higher than the predicted concentration of 0.0311 mg/mL. In conclusion, the relationship between the selected optimization parameters strongly influenced the level of MPT64 gene expression in E. coli BL21 (DE3).

Dual-aptamer-based voltammetric biosensor for the Mycobacterium tuberculosis antigen MPT64 by using a gold electrode modified with a peroxidase loaded composite consisting of gold nanoparticles and a Zr(IV)/terephthalate metal-organic framework

An ultrasensitive aptasensor is described for the voltammetric determination of the Mycobacterium tuberculosis antigen MPT64 in human serum. Firstly, an amino-modified Zr(IV) based metal-organic framework (MOF; type UiO-66-NH₂; made up from Zr₆O₃₂ units and 2-amino-terephthalate linkers) with a high specific surface was synthesized and used as the carrier of the gold nanoparticles and the aptamers. Then the signalling nanoprobe was fabricated after the horseradish peroxidase was cast on the nanomaterials. The two aptamers with synergistic effect on binding MPT64 were anchored on the gold electrode. Differential pulse voltammetry indicated that the peak current is highest if the ratio of the two aptamers is 1:1. The assay has a wide linear response range (0.02 to 1000 pg·mL^-1 of MPT64) and a 10 fg·mL^-1 detection limit at a working potential of around -96 mV (vs Ag/AgCl). The results show this biosensor to be a viable tool for detection of tuberculosis at an early stage. Graphical abstract Schematic presentation of the construction of the nanoprobe and biosensor. Firstly, the surface of UiO-66-NH₂ was anchored to gold nanoparticles (AuNPs). A dual-aptamer and HRP were added to form the signalling nanoprobe (Aptamer/HRP/AuNPs/UiO-66-NH₂). Then, the aptamers I and II were attached on the surface of gold electrode and 6-mercapto-1-hexanol was used to block the uncovered active site of the gold electrode. Finally, after incubation with MPT64, the signalling nanoprobe was dropped on the modified electrode and the DPV measurements was used for the analysis of Mycobacterium tuberculosis antigen MPT64. (PVP: poly(vinyl pyrrolidone); HRP: horseradish peroxidase; MCH: 6-Mercapto-1-hexanol; HQ: hydroquinone; BQ: benzoquinone).

Use of an immunochromatographic assay for rapid identification of Mycobacterium tuberculosis complex clinical isolates in routine diagnosis

Accurate identification of Mycobacterium tuberculosis complex (MTBC) isolates is essential for tuberculosis (TB) control, especially in a high-burden country such as Brazil. Conventional identification methods are laborious and time-consuming, while rapid molecular methods are expensive and require skilled personnel and appropriate physical laboratory infrastructure. Immunochromatographic assays (ICAs) have been shown to provide a rapid and reliable TB diagnosis at a low cost. The use of the SD Bioline TB Ag MPT64 ICA (MPT64 assay) for rapid identification of MTBC clinical isolates in the routine diagnosis of a large-volume reference TB laboratory was evaluated. We analysed 375 isolates on solid and liquid media concurrently with conventional phenotypic methods, the PRA-hsp65 molecular technique and the MPT64 assay. The sensitivity, specificity and accuracy of the ICA were 97.7, 100 and 98.1 %, respectively. The MPT64 assay yielded rapid and accurate results, enabling the treatment to be initiated early and also impacting on TB control.

Selection, characterization, and application of DNA aptamers for detection of Mycobacterium tuberculosis secreted protein MPT64

Rapid detection of Mycobacterium tuberculosis (Mtb), an etiological agent of tuberculosis (TB), is important for global control of this disease. Aptamers have emerged as a potential rival for antibodies in therapeutics, diagnostics and biosensing due to their inherent characteristics. The aim of the current study was to select and characterize single-stranded DNA aptamers against MPT64 protein, one of the predominant secreted proteins of Mtb pathogen. Aptamers specific to MPT64 protein were selected in vitro using systematic evolution of ligands through exponential enrichment (SELEX) method. The selection was started with a pool of ssDNA library with randomized 40-nucleotide region. A total of 10 cycles were performed and seventeen aptamers with unique sequences were identified by sequencing. Dot Blot analysis was performed to monitor the SELEX process and to conduct the preliminary tests on the affinity and specificity of aptamers. Enzyme linked oligonucleotide assay (ELONA) showed that most of the aptamers were specific to the MPT64 protein with a linear correlation of R² = 0.94 for the most selective. Using Surface Plasmon Resonance (SPR), dissociation equilibrium constant K_D of 8.92 nM was obtained. Bioinformatics analysis of the most specific aptamers revealed the existence of a conserved as well as distinct sequences and possible binding site on MPT64. The specificity was determined by testing non-target ESAT-6 and CFP-10. Negligible cross-reactivity confirmed the high specificity of the selected aptamer. The selected aptamer was further tested on clinical sputum samples using ELONA and had sensitivity and specificity of 91.3% and 90%, respectively. Microscopy, culture positivity and nucleotide amplification methods were used as reference standards. The aptamers studied could be further used for the development of medical diagnostic tools and detection assays for Mtb.

High level of IFN-γ released from whole blood of human tuberculosis infections following stimulation with Rv2073c of Mycobacterium tuberculosis

More efficacious and specific biomarkers are urgently needed for better control of tuberculosis (TB), the second leading infectious cause of mortality worldwide. The region of difference 9 (RD9) presents the genome of the causative pathogen Mycobacterium tuberculosis rather than other species of the genus Mycobacterium, which might be promising targets for specific diagnosis, vaccine development and pathogenesis. In this study, two proteins Rv2073c and Rv2074, encoded by the RD9 were expressed and purified from Escherichia coli system. Following stimulation with both proteins, the levels of IFN-γ secreted by T cells from a total of 49 whole blood samples obtained from clinically diagnosed active TB patients, patients with latent TB infections (LTBIs), and healthy donors, were compared with those of the incubation with recombinant fusion protein of CFP21 and MPT64 (rCM). Our results demonstrated that only Rv2073c could induce a higher level of IFN-γ in TB infections than healthy controls and there was a positive correlation between Rv2073c- and rCM-specific IFN-γ levels in TB infections and healthy donors, respectively. These findings indicate that Rv2073c might be a promising antigen for specific diagnostic reagents and vaccine candidates of TB.